Registration Dossier

Diss Factsheets

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
85 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
1
Modified dose descriptor starting point:
NOAEC
Value:
85 mg/m³
AF for dose response relationship:
1
Justification:
The database for this endpoint encompasses a range of exposure conditions allowing information on the time- and exposure-response relationship and severity to be obtained. On this basis, it is not necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.
AF for differences in duration of exposure:
1
Justification:
It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
1
Justification:
There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in workers. Since the dose descriptor reflects findings from a large cohort study the data already addresses human variability and hence a factor of 1 has been selected to take account of the intraspecies variability within the worker population. The factor of 1 corresponds to the recommendation of ECETOC (2010).
AF for the quality of the whole database:
1
Justification:
Since the information is based on a rigorous and well-reported study, it is not necessary to apply an assessment factor to take account of uncertainties arising from poor quality information.
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
289 mg/m³
Most sensitive endpoint:
acute toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
3
Modified dose descriptor starting point:
NOAEC
Value:
863 mg/m³
AF for dose response relationship:
1
Justification:
The starting point is a NOAEC. Minor impairments in neurobehavioural test performances were reported for volunteers exposed to concentrations of around 200 ppm for 1 hour. These data support the conclusion that 100 ppm can be regarded as a NOAEC for a 7-hour exposure and suggest that the dose-response relationship for CNS depression is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
3
Justification:
There are no data to quantify variability in susceptibility to the CNS depressant effects of styrene in workers. In the absence of substance specific data the default factor of 3 as proposed by ECETOC will be used to take account of differences in susceptibility between workers for the CNS depressant effects of styrene.
AF for the quality of the whole database:
1
Justification:
The quality of the database for this endpoint is adequate. The key study is a human volunteer study the results of which show a dose-related trend for increasing severity with increasing dose. The results of the key study are supported by data from several additional human volunteer studies conducted by separate groups of researchers. This consistency provides confidence in the reliability of these studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Local effects

Long term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
306 mg/m³
Most sensitive endpoint:
acute toxicity
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
3
Dose descriptor starting point:
NOAEC
AF for dose response relationship:
1
Justification:
The starting point is a NOAEC. In this study, volunteers exposed to 100 ppm for 1 hour did not report irritation but when the exposure period was extended to 7 hours, mild and transient eye irritation was reported. There were no reports of irritation in volunteers exposed to 216 ppm for 1 hour and hence it was concluded in the UK RAR (2008) that the irritation reported by volunteers exposed to 100 ppm for 7 hours may have been due to eye dryness rather than primary irritation. At 375 ppm, 4 out of 9 volunteers reported mild eye irritation and all reported nasal irritation. These findings indicate that the dose-response relationship for irritation is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
3
Justification:
There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. Since irritant effects relate to the concentration at the target site it is not necessary to apply a factor to take account of toxicokinetic differences. In relation to toxicodynamic differences, the IPCS recommends a factor of 3.16 to account for differences within the human population (IPCS, 2005). This factor of 3 corresponds also to the proposal of ECETOC (2003).
AF for the quality of the whole database:
1
Justification:
The quality of the database for this endpoint is adequate. A range of concentrations and exposure durations were tested in the key study. The results were internally consistent and were supported by results obtained in two separate but small scale human volunteer studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
406 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
ECHA REACH Guidance
Overall assessment factor (AF):
1
Modified dose descriptor starting point:
NOAEL
Value:
406 mg/kg bw/day
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:
low hazard (no threshold derived)

Additional information - workers

The purpose of this transitional dossier is to develop risk reduction strategies for exposure situations, for which conclusion was reached in the UK RAR (2008). Therefore, DNELs have only been calculated for the health endpoints and routes of exposure that are relevant to the exposure scenarios of concern identified in the UK RAR.

 

Overview of dose descriptors

The human health endpoints for which concerns have been identified in the UK RAR (2008) are:

- acute toxicity (CNS depression)

- skin, eye and respiratory tract irritation

- effects on colour vision discrimination following repeated exposure

- effects on hearing (ototoxicity) following repeated exposure

- developmental toxicity

The dose descriptors that were identified in the UK RAR for these endpoints are summarised in the table below. In relation to skin and eye irritation as a result of direct contact with liquid styrene, the available data do not provide sufficient information to characterise the dose-response relationship for this effect. It is therefore not possible to derive a DNEL or DMEL for this endpoint. In accordance with the REACH Chemical Safety Assessment (CSA) guidance (Chapter R8, P122 and Part E, table E 3.1) the irritant potency, as indicated by the assigned R-phrases R36 (irritating to the eyes) and R38 (irritating to the skin) will be used to identify suitable risk management measures. This will be considered further in the risk characterisation.

 

DNELs are given here as ppm values. If appropriate, DNELs are additionally given as mg/m3 values. The conversion ppm to mg/m3 is based on the following formula: 1 ppm = 4.25 mg/m3.

 

Dose descriptors identified in the UK RAR (2008) for endpoints of concern

Endpoint

Quantitative dose descriptor or other information on potency

Associated relevant effect

Remarks on the study

Local effect

Systemic effect

Acute toxicity

Inhalation

 

NOAEC 100 ppm (7-hour)

CNS depression

Human volunteer data

Irritation/corrosivity

Eye

NOAEC 216 ppm (1-hour)

 

Eye and respiratory tract irritation from airborne vapour

Human volunteer data

Respiratory tract

Repeated dose toxicity (sub-acute/sub-chronic/chronic)

Inhalation

(human)

 

NOAEC 50 ppm (8-hour TWA)

Effects on colour vision discrimination

Obtained from studies in workers using tests specifically designed to evaluate colour vision. This NOAEC is supported by Seeber et al. (2009) in workers with high exposures of 50 ppm.

Inhalation (animal)

 

NOAEC 500 ppm

Effects on hearing (ototoxicity)

4 week study in the rat, exposure for 6 hours per day, 5 days per week. 

Inhalation (human)

 

NOAEC 38.8 – 48.5 ppm (up to 10 years)

LOAEC 25 – 33 ppm (up to 26 years)

Effects on hearing (ototoxicity)

Obtained from a study in workers (Triebig et al., 2009)

Developmental toxicity

Inhalation

 

F1-generation (excluding pups exposed by inhalation: NOAEC 500 ppm

 

2-generation study in the rat, exposure 6 hours per day, 7 days per week.

F2-generation: NOAEC 150 ppm

 

 

 

1) Worker-DNEL short-term inhalation route

Peak airborne exposure to styrene vapour causes both local and systemic effects. It is therefore necessary to calculate DNELs for both types of effect to determine which will be the critical health endpoint for the risk assessment of short-term exposure.

 

1.1) DNEL based on local effects (eye and respiratory tract irritation from the vapour)

The dose descriptor is the NOAEC of 216 ppm obtained from a study with 9 human volunteers exposed for 1 hour (Stewart et al., 1969). Irritation is a concentration specific effect, it is therefore not necessary to modify the dose descriptor to take account of differences in breathing rates between volunteers at rest and active workers. It is also not necessary to modify the dose descriptor to take account of the difference in dose that will be obtained from the 1-hour exposure of the volunteers and the 15-minute reference period for the short-term DNEL. The starting point is therefore 216 ppm.

 

Assessment factors and DNEL calculation for worker-DNEL short-term inhalation local effects

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

3

There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. Since irritant effects relate to the concentration at the target site it is not necessary to apply a factor to take account of toxicokinetic differences. In relation to toxicodynamic differences, the IPCS recommends a factor of 3.16 to account for differences within the human population (IPCS, 2005). This factor of 3 corresponds also to the proposal of ECETOC (2003).

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure.

Dose response and endpoint specific/severity issues

1

The starting point is a NOAEC. In this study, volunteers exposed to 100 ppm for 1 hour did not report irritation but when the exposure period was extended to 7 hours, mild and transient eye irritation was reported. There were no reports of irritation in volunteers exposed to 216 ppm for 1 hour and hence it was concluded in the UK RAR (2008) that the irritation reported by volunteers exposed to 100 ppm for 7 hours may have been due to eye dryness rather than primary irritation. At 375 ppm, 4 out of 9 volunteers reported mild eye irritation and all reported nasal irritation. These findings indicate that the dose-response relationship for irritation is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.

Quality of database

1

The quality of the database for this endpoint is adequate. A range of concentrations and exposure durations were tested in the key study. The results were internally consistent and were supported by results obtained in two separate but small scale human volunteer studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Overall assessment factor: 3

Endpoint specific DNEL: 216/3 = 72 ppm, equivalent to 306 mg/m3

 

 

1.2) DNEL based on systemic effects (CNS depression)

The dose descriptor is the NOAEC of 100 ppm obtained from a study with 6 human volunteers exposed for 7 hours (Stewart et al., 1968). CNS depression is a dose-dependent effect. It is therefore necessary to adjust the NOAEC by a factor of 0.67 to take account of the different doses that will be received due to differences in breathing rates between volunteers at rest and workers engaged in light activity.

100 x 0.67 = 67 ppm (7 hours)

Since the short-term inhalation DNEL has a 15 minute reference period it is also necessary to convert the 7-hour NOAEC to an equivalent dose that would be inhaled over a 15 minute period. This is done using the modified Haber’s rule cnt = k (TGD, Chapter R8, Appendix R8-8, page 108) where ‘c’ is the concentration, ‘t’ is the exposure time, ‘n’ is a regression coefficient and ‘k’ is a constant. It is not possible to determine an appropriate value for ‘n’ from the available data, therefore the default value of 3 to extrapolate from a longer to shorter exposure period will be used.

3 (673 x 7 x 4) = 203 ppm (15 minutes)

The corrected starting point is 203 ppm (15 minutes)

 

Assessment factors and DNEL calculation for worker DNEL short-term inhalation systemic effects

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

3

There are no data to quantify variability in susceptibility to the CNS depressant effects of styrene in workers. In the absence of substance specific data the default factor of 3 as proposed by ECETOC will be used to take account of differences in susceptibility between workers for the CNS depressant effects of styrene.

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure.

Dose response and endpoint specific/severity issues

1

The starting point is a NOAEC. Minor impairments in neurobehavioural test performances were reported for volunteers exposed to concentrations of around 200 ppm for 1 hour. These data support the conclusion that 100 ppm can be regarded as a NOAEC for a 7-hour exposure and suggest that the dose-response relationship for CNS depression is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.

Quality of database

1

The quality of the database for this endpoint is adequate. The key study is a human volunteer study the results of which show a dose-related trend for increasing severity with increasing dose. The results of the key study are supported by data from several additional human volunteer studies conducted by separate groups of researchers. This consistency provides confidence in the reliability of these studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Overall assessment factor: 3

Endpoint specific DNEL: 203/3 = 68 ppm, equivalent to 289 mg/m3

 

 

1.3) Selection of worker-DNEL short-term inhalation

A DNEL of 72 ppm was calculated for eye and respiratory tract irritation compared to a DNEL of 68 ppm for CNS depression. CNS depression is therefore identified as the critical health effect for the risk assessment of short-term exposure.

The worker DNEL short-term inhalation route is 70 ppm (15-minute reference period), equivalent to 297.5 mg/m3.

 

 

2) Worker-DNEL long-term inhalation route

The UK RAR (2008) concluded that long-term repeated exposure to styrene has the potential to cause effects on colour vision discrimination, ototoxicity and developmental toxicity. A dose descriptor for effects on colour vision discrimination and partly also on ototoxicity has been identified from studies on workers. The available human data relating to developmental toxicity do not provide sufficient information to allow a human dose descriptor to be identified for this endpoint. A dose descriptor for this endpoint has been identified from animal data. Since the dose-response relationship and evidence base for each endpoint is different it is not clear which is the critical endpoint for risk assessment of long-term repeated exposure. It will therefore be necessary to calculate separate endpoint specific DNELs for each effect to identify the critical long-term DNEL.

 

 

 

2.1) Endpoint specific DNEL for effects on colour vision

There is an extensive body of data in the UK RAR (2008) on the effects of exposure to styrene on colour vision discrimination obtained from studies using tests specifically designed to examine this endpoint. A NOAEC of 50 ppm (8-hr TWA) was identified from studies discussed in the UK RAR and further supported by a recent investigation of Seeber et al. (2009). Since this dose descriptor was obtained from studies of workers it is not necessary to modify the dose descriptor. The starting point is therefore 50 ppm.

 

Assessment factors and DNEL calculation for worker DNEL long-term inhalation for effects on colour vision

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

1

There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in workers. Since the dose descriptor reflects findings from a number of studies covering in total hundreds of workers from several nationalities the data already addresses human variability and hence a factor of 1 has been selected to take account of the intraspecies variability within the worker population. The factor of 1 corresponds to the recommendation of ECETOC (2010).

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.

Dose response and endpoint specific/severity issues

1

The extensive database for this endpoint encompasses a range of exposure conditions allowing information on the exposure-response relationship and severity to be obtained. The UK RAR (2008) concluded that no changes in colour vision discrimination would be expected with 8-hour TWA exposures below 20 ppm. In some of the studies before 2009 effects were reported at exposures below 50 ppm. But the exposure assessments are less reliable than those of the workforce studied by Seeeber et al. (2009) who did not find colour vision deficiencies at exposures up to 50–100 ppm. Furthermore, in all studies when slight changes were detected in tests, the effects were reversible, the individuals concerned were not aware of any deficit and there was no indication that performance was affected in jobs requiring good colour discrimination. The data at higher levels of exposure was not considered to be sufficiently robust to reliably characterise the scale and nature of the effect. On this basis and given that the effects are reversible, it is not considered necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.

Quality of database

1

Since the database for this endpoint includes rigorous and well-reported studies, it is not considered necessary to apply an assessment factor to take account of uncertainties arising from poor quality information. 

Overall assessment factor:  1

Endpoint specific DNEL: 50/1 = 50 ppm, equivalent to 212.5 mg/m3

 

 

2.2) Endpoint specific DNEL for ototoxicity

Studies have been conducted in workers and in laboratory animals to investigate the potential for exposure to styrene to have an adverse effect on hearing. In studies before 2009 limited evidence was obtained for styrene-induced hearing loss in workers but due to co-exposure to noise and other solvents and insufficient exposure data in these studies it was not possible to establish a clear dose-response relationship. In the study of Triebig et al. (2009) no hearing deficits were found for exposures of 12.5 ppm and 50 ppm at the time of investigation going back to about 10 years. On the other hand, there was an indication for styrene induced hearing losses in a subgroup of “high-long” exposed workers assumed to be exposed at 25-33 ppm over about 15 years (range up to 26 years). Higher exposures of 80-100 ppm existed for a time more than 10 years before this study was initiated. Taking into account the irreversibility of styrene induced hearing deficits, these effects are considered to stem from the former high exposures. In summary a NOAEC for humans of 20 ppm can be derived as starting point from this study.

There is clear evidence from studies in laboratory animals that styrene has a specific adverse effect on hearing. The effect is characterised by an elevation of hearing thresholds across particular frequencies and is the result of irreversible damage within the ear. This occurs because styrene selectively destroys hair cells in the cochlea possibly because of an effect on the membranous organisation of these cells. It is assumed that the effects seen in animals are of relevance for humans. Studies in rats have indicated that hearing loss occurs within a few days of the start of exposure and although it does not increase in severity with continued exposure, the initial effect is irreversible. A NOAEC of 500 ppm was identified in the UK RAR (2008) and this will be used as the starting point for the derivation of DNELs for ototoxicity based on animal studies. But it has to be taken into consideration that Lataye et al. (2005) did observe minor hair cell loss in the cochlea at 500 ppm.

If the DNEL is derived from studies on exposed workers an adjustment of the starting point is not necessary.

Using animal studies to derive the DNEL it has to be taken into account that animals were exposed for 6 hour per day whereas workers may be exposed for up to 8 hours per day. Therefore it is necessary to adjust the starting point for workers by a factor of 0.75 to take account of differences in the dose that will be obtained over the daily exposure period. It is also necessary to adjust the starting point for workers by a factor of 0.67 to take account of differences in inhalation rates between animals at rest and humans involved in light activity.

The corrected starting point for animal studies is therefore:

500 ppm x 0.75 x 0.67 = 251 ppm (8-hours).

Maekitie (1997) identified a NOAEC of 300 ppm in rats exposed for 12 h/d, 5 d/week over 4 weeks. This study would lead to a corrected starting point of 300 x 12/8 x 0.67=301 ppm. But only crude data were given for outer hair cell loss in the cochlea in comparison to Lataye et al. (2005). Therefore, for DNEL calculation based on animal data the lower corrected starting point of 251 ppm is used as proposed by.

 

Assessment factors and DNEL calculation for worker DNEL long-term inhalation for ototoxicity based on animal studies

Uncertainties

AF

Justification

Interspecies differences

1

For interspecies variability the assessment factors proposed by ECETOC (2003, 2010) are used. The dose descriptor was obtained from an inhalation study and is being used to derive an inhalation DNEL. It is therefore not necessary to apply an allometric scaling factor to take account of differences in basal metabolic rates between animals and humans. According to ECETOC the additional assessment factor of 2.5 to quantify other differences between animals and humans that could affect interspecies extrapolation is scientifically not justified and a factor of 1 is appropriate. On this basis the default factor of 1 to account for other species differences will be applied.

Intraspecies differences

3

For intraspecies variability the assessment factor proposed by ECETOC (2003, 2010) is used. There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in the human population. The default factor of 3 for workers as proposed by ECETOC will therefore be used to take account of intraspecies variability.

In total there is a combined inter- and intraspecies assessment factor of 3 that takes into account that the target tissue (outer hair cells in the cochlea, anatomical structure and blood supply of the cochlea) is identical in rats and humans.

Differences in duration of exposure

1

The dose descriptor was obtained from a 4 week study. Although the DNEL is to be used to assess long-term repeated exposure there is strong evidence showing that the ototoxic effects of styrene occur within a week of initial exposure and do not progress in severity with further exposure. On this basis, the duration of this study is adequate for the endpoint being studied and it is not necessary to apply a factor to take account of differences in duration of exposure.

Dose response and endpoint specific/severity issues

2

Several studies have been conducted in the rat to investigate ototoxicity. The studies encompass a range of concentrations and durations of exposure and provide reliable information on the dose-response relationship and severity of effect. The effect is characterised by an elevation of hearing thresholds and is the result of irreversible damage within the cochlea. In the UK RAR (2008) a NOAEC for hearing threshold of 500 ppm has been identified in the key study. But as minor histopathological alterations were found at 500 ppm an assessment factor of 2 is used. At higher exposure levels, hearing thresholds were increased and the level of increase correlated with dose. Minor shifts of 1-3 dB were reported in rats exposed to around 600 ppm increasing to threshold shifts of 35 – 40 dB at concentrations of 800 – 1000 ppm.

Quality of database

1

The findings from the key study are supported by findings from several additional studies conducted to modern regulatory standards by separate groups of researchers. On this basis the quality of the database is not considered to contribute uncertainty and it is therefore not necessary to apply an additional factor.  

Overall assessment factor:  6

Endpoint specific DNEL: 251/6 = 42 ppm (8-hours) , equivalent to 178.5 mg/m3

 

Assessment factors and DNEL calculation for worker DNEL long-term inhalation for ototoxicity based on human data

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

1

There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in workers. Since the dose descriptor reflects findings from a large cohort study the data already addresses human variability and hence a factor of 1 has been selected to take account of the intraspecies variability within the worker population. The factor of 1 corresponds to the recommendation of ECETOC (2010).

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.

Dose response and endpoint specific/severity issues

1

The database for this endpoint encompasses a range of exposure conditions allowing information on the time- and exposure-response relationship and severity to be obtained. On this basis, it is not necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.

Quality of database

1

Since the information is based on a rigorous and well-reported study, it is not necessary to apply an assessment factor to take account of uncertainties arising from poor quality information. 

Overall assessment factor:  1

Endpoint specific DNEL: 20/1 = 20 ppm, equivalent to 85 mg/m3

 

In conclusion, a worker DNEL long-term inhalation for ototoxicity of 20 ppm is proposed based on data obtained by a cohort study on exposed workers. This is to be considered sufficiently conservative in comparison to a DNEL derived from a large animal database, i.e. 42 ppm.

 

 

2.3) Endpoint specific DNEL for developmental toxicity

A NOAEC of 150 ppm has been identified for developmental toxicity in a 2 -generation reproductive toxicity study in which rats were exposed for 6 hours per day, 7 days per week (Cruzan et al., 2005a, b).

 

It has to be taken into consideration that the exposure scenarios for specific life stages in the 2-generation study are not relevant for derivation of a DNEL long-tem for workers. The following exposure situations do not apply for the workplace:

direct exposure of pups by inhalation for the time between weaning and puberty as occurred in F1 pups

exposure of parental animals from weaning to puberty as occurred in F1 animals producing the F2 generation.

Therefore the NOAEC must not be taken from the F2 generation, if differences exist between those of F1 and F2 offspring. Furthermore, if there are effects occurring only in F1 offspring after weaning with direct inhalation exposure, these are irrelevant for defining a worker DNEL. On the other hand, effects found in F1 offspring during the nursing period have to be taken into account for the human situation if in exceptional cases maternal leave is not taken.

No exposure related effects were observed in F1 offspring during the nursing period up to weaning. Therefore the highest exposure concentration of 500 ppm is taken as NOAEC. This is a conservative starting point as the “real” NOAEC is higher, but the difference between 500 ppm and the “real” NOAEC cannot be quantified.

Since animals were exposed for 6 hours per day, whereas workers may be exposed for up to 8 hours per day, it is necessary to adjust the starting point by a factor of 0.75. To take account of the fact that animals were exposed for 7 days whereas the working week is assumed to be 5 days duration, the starting point will be adjusted by a factor of 7/5 (1.4). It is also necessary to adjust the starting point for workers by a factor of 0.67 to take account of differences in inhalation rates between animals at rest and humans undertaking light activity.

The corrected starting point is therefore:

500 ppm x 0.75 x 1.4 x 0.67 = 352 ppm (8-hours)

 

Assessment factors and DNEL calculation for worker DNEL long-term inhalation for developmental toxicity

Uncertainties

AF

Justification

Interspecies differences

1

For interspecies variability the assessment factors proposed by ECETOC (2003, 2010) are used. The dose descriptor was obtained from an inhalation study and is being used to derive an inhalation DNEL. It is therefore not necessary to apply an allometric scaling factor to take account of differences in basal metabolic rates between animals and humans. According to ECETOC the additional assessment factor of 2.5 to quantify other differences between animals and humans that could affect interspecies extrapolation is scientifically not justified and a factor of 1 is appropriate. On this basis the default factor of 1 to account for other species differences will be applied.

Intraspecies differences

3

For intraspecies variability the assessment factor proposed by ECETOC (2003, 2010) is used. There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in the human population. The default factor of 3 for workers as proposed by ECETOC will therefore be used to take account of intraspecies variability.

Differences in duration of exposure

1

The NOAEC was derived from the 2-generation study starting from exposure of young adult animals of the F0 generation up to weaning of the F1 generation. This represents a worst case scenario for workers being exposed to styrene from the start of their working life, during pregnancy up to the end of the breast feeding period without a maternity leave. An assessment factor of 1 is therefore appropriate.

Dose response and endpoint specific/severity issues

1

As 500 ppm was a clear NOAEC for developmental effects in F1 offspring before weaning and start of direct inhalation exposure, an assessment factor is not warranted in this respect.

Quality of database

1

The key study was conducted to modern regulatory standards and was adequately reported. The findings are supported by results from other studies conducted to modern regulatory standards. On this basis the quality of the database is not considered to contribute uncertainty and it is therefore not necessary to apply an additional factor.     

Overall assessment factor:  3

Endpoint specific DNEL: 352/3 = 117 ppm (8-hour), equivalent to 497.25 mg/m3

 

 

2.4) Selection of worker-DNEL long-term inhalation

The most sensitive endpoint-specific DNEL is that for ototoxicity derived from observations in workers. This endpoint is relevant for workers. So the endpoint specific DNEL for ototoxicity is identified as the worker-DNEL long-term inhalation.

The worker DNEL long-term inhalation route is 20 ppm (8-hr TWA).

 

 

 

3) Worker-DNEL long-term dermal route

Styrene has the potential to be absorbed across the skin and there is the potential for adverse systemic effects to arise as a result of skin exposure. No studies have been undertaken by the dermal route to characterise the dose-response relationship for systemic effects therefore it will be necessary to obtain a long-term dermal DNEL by route-to-route extrapolation. Since ototoxicity has been identified as the critical health endpoint for long-term inhalation exposure, this endpoint will also be the critical endpoint for long-term dermal exposure. The DNEL derived from studies in workers was 20 ppm, corresponding to 86 mg/m³. Using a respiratory volume for workers under light physical activity of 10 m³/person/day and a body weight of 70 kg (ECHA, 2008) the external exposure would be 86 x 10/70 = 12.3 mg/kg/d.

It is necessary to convert this inhalative dose to an equivalent dermal dose. The UK RAR (2008) concluded that there is 100 % absorption of styrene from the respiratory tract but in humans only 2 % of a dermal dose of liquid styrene is likely to be absorbed. The corrected dermal NOAEL therefore would be:

12.3 x 100/2 = 615 mg/kg/day

ECHA (2008) proposes to take a limited absorption rate for the starting route, leading to a low (conservative) internal NOAEL. Engström et al. (1978a) investigated the uptake of styrene in 7 volunteers at 50 ppm at rest and under physical activity (50 - 150 Watt). Under light activity (50 Watt) the uptake was 66% leading to a corrected dermal NOAEL of

12.3 x 66/2 = 406 mg/kg/d.

Since the worker-DNEL long-term for dermal exposure was directly derived from that for inhalation exposure no further assessment factors are necessary.

The worker DNEL long-term dermal route for systemic effects is 406 mg/kg/day.

This DNEL does not address the potential for local irritation. The risk characterisation will consider whether specific risk management measures are necessary to protect against local effects.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
10.2 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
3
Modified dose descriptor starting point:
NOAEC
Value:
212.5 mg/m³
AF for dose response relationship:
1
Justification:
The database for this endpoint encompasses a range of exposure conditions allowing information on the time- and exposure-response relationship and severity to be obtained. On this basis, it is not necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.
AF for differences in duration of exposure:
1
Justification:
It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
3
Justification:
There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in consumers. Since the dose descriptor reflects findings from a number of studies covering in total hundreds of workers from several nationalities the data already addresses variability in workers and hence a factor of 3 has been selected to take account of the possible additional intraspecies variability within the consumer population. The factor of 3 corresponds to the recommendation of ECETOC (2010) for extrapolation from workers to consumers based on human data.
AF for the quality of the whole database:
1
Justification:
Since the information is based on a rigorous and well-reported study, it is not necessary to apply an assessment factor to take account of uncertainties arising from poor quality information.
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
174.25 mg/m³
Most sensitive endpoint:
acute toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
5
Modified dose descriptor starting point:
NOAEC
Value:
863 mg/m³
AF for dose response relationship:
1
Justification:
The starting point is a NOAEC. Minor impairments in neurobehavioural test performances were reported for volunteers exposed to concentrations of around 200 ppm for 1 hour. These data support the conclusion that 100 ppm can be regarded as a NOAEC for a 7-hour exposure and suggest that the dose-response relationship for CNS depression is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
5
Justification:
There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. For local effects by inhalation ECETOC proposes an assessment factor of 5 for intraspecies variability when starting from animal data. Taking into account that an assessment factor of 3 was used for workers this higher factor of 5 is appropriate for consumers.
AF for the quality of the whole database:
1
Justification:
The quality of the database for this endpoint is adequate. The key study is a human volunteer study the results of which show a dose-related trend for increasing severity with increasing dose. The results of the key study are supported by data from several additional human volunteer studies conducted by separate groups of researchers. This consistency provides confidence in the reliability of these studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Local effects

Long term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
182.75 mg/m³
Most sensitive endpoint:
acute toxicity
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
5
Dose descriptor starting point:
NOAEC
AF for dose response relationship:
1
Justification:
The starting point is a NOAEC. In this study, volunteers exposed to 100 ppm for 1 hour did not report irritation but when the exposure period was extended to 7 hours, mild and transient eye irritation was reported. There were no reports of irritation in volunteers exposed to 216 ppm for 1 hour and hence it was concluded in the UK RAR (2008) that the irritation reported by volunteers exposed to 100 ppm for 7 hours may have been due to eye dryness rather than primary irritation. At 375 ppm, 4 out of 9 volunteers reported mild eye irritation and all reported nasal irritation. These findings indicate that the dose-response relationship for irritation is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.
Justification:
The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.
AF for intraspecies differences:
5
Justification:
There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. For local effects by inhalation ECETOC proposes an assessment factor of 5 for intraspecies variability when starting from animal data. Taking into account that an assessment factor of 3 was used for workers this higher factor of 5 is appropriate for consumers.
AF for the quality of the whole database:
1
Justification:
The quality of the database for this endpoint is adequate. A range of concentrations and exposure durations were tested in the key study. The results were internally consistent and were supported by results obtained in two separate but small scale human volunteer studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

General Population - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
343 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
ECHA REACH Guidance
Overall assessment factor (AF):
1
Modified dose descriptor starting point:
NOAEL
Value:
521 mg/kg bw/day
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
2.1 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
By inhalation
DNEL related information
DNEL derivation method:
other: ECETOC
Overall assessment factor (AF):
1
Modified dose descriptor starting point:
NOAEL
Value:
2.1 mg/kg bw/day
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:
low hazard (no threshold derived)

Additional information - General Population

The purpose of this transitional dossier is to develop risk reduction strategies for exposure situations, for which conclusion was reached in the UK RAR (2008). Therefore, DNELs have only been calculated for the health endpoints and routes of exposure that are relevant to the exposure scenarios of concern identified in the UK RAR.

 

Overview of dose descriptors

The human health endpoints for which concerns have been identified in the UK RAR (2008) are:

- acute toxicity (CNS depression)

- skin, eye and respiratory tract irritation

- effects on colour vision discrimination following repeated exposure

- effects on hearing (ototoxicity) following repeated exposure

- developmental toxicity

The dose descriptors that were identified in the UK RAR for these endpoints are summarised in the table below. In relation to skin and eye irritation as a result of direct contact with liquid styrene, the available data do not provide sufficient information to characterise the dose-response relationship for this effect. It is therefore not possible to derive a DNEL or DMEL for this endpoint. In accordance with the REACH Chemical Safety Assessment (CSA) guidance (Chapter R8, P122 and Part E, table E 3.1) the irritant potency, as indicated by the assigned R-phrases R36 (irritating to the eyes) and R38 (irritating to the skin) will be used to identify suitable risk management measures. This will be considered further in the risk characterisation.

 

DNELs are given here as ppm values. If appropriate, DNELs are additionally given as mg/m3 values. The conversion ppm to mg/m3 is based on the following formula: 1 ppm = 4.25 mg/m3.

 

Dose descriptors identified in the UK RAR (2008) for endpoints of concern

Endpoint

Quantitative dose descriptor or other information on potency

Associated relevant effect

Remarks on the study

Local effect

Systemic effect

Acute toxicity

Inhalation

 

NOAEC 100 ppm (7-hour)

CNS depression

Human volunteer data

Irritation/corrosivity

Eye

NOAEC 216 ppm (1-hour)

 

Eye and respiratory tract irritation from airborne vapour

Human volunteer data

Respiratory tract

Repeated dose toxicity (sub-acute/sub-chronic/chronic)

Inhalation

(human)

 

NOAEC 50 ppm (8-hour TWA)

Effects on colour vision discrimination

Obtained from studies in workers using tests specifically designed to evaluate colour vision. This NOAEC is supported by Seeber et al. (2009) in workers with high exposures of 50 ppm.

Inhalation (animal)

 

NOAEC 500 ppm

Effects on hearing (ototoxicity)

4 week study in the rat, exposure for 6 hours per day, 5 days per week. 

Inhalation (human)

 

NOAEC 38.8 – 48.5 ppm (up to 10 years)

LOAEC 25 – 33 ppm (up to 26 years)

Effects on hearing (ototoxicity)

Obtained from a study in workers (Triebig et al., 2009)

Developmental toxicity

Inhalation

 

F1-generation (excluding pups exposed by inhalation: NOAEC 500 ppm

 

2-generation study in the rat, exposure 6 hours per day, 7 days per week.

F2-generation: NOAEC 150 ppm

 

 

 

1) Consumer-DNEL short-term inhalation route

Peak airborne exposure to styrene vapour causes both local and systemic effects. It is therefore necessary to calculate DNELs for both types of effect to determine which will be the critical health endpoint for the risk assessment of short-term exposure.

Since the consumer exposure scenarios of concern relate to DIY tasks, exposure will occur under conditions of light activity. If appropriate, it is therefore necessary to adjust the NOAEC by a factor of 0.67 to take account of the different doses that will be received due to differences in breathing rates between volunteers at rest and consumers (DIY) engaged in light activity.

 

1.1) DNEL based on local effects (eye and respiratory tract irritation from the vapour)

The dose descriptor is the NOAEC of 216 ppm obtained from a study with 9 human volunteers exposed for 1 hour (Stewart et al., 1969). Irritation is a concentration specific effect, it is therefore not necessary to modify the dose descriptor to take account of differences in breathing rates between volunteers at rest and consumers performing DIY tasks. It is also not necessary to modify the dose descriptor to take account of the difference in dose that will be obtained from the 1-hour exposure of the volunteers and the 15-minute reference period for the short-term DNEL. The starting point is therefore 216 ppm.

 

Assessment factors and DNEL calculation for consumer-DNEL short-term inhalation local effects

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

5

There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. For local effects by inhalation ECETOC proposes an assessment factor of 5 for intraspecies variability when starting from animal data. Taking into account that an assessment factor of 3 was used for workers this higher factor of 5 is appropriate for consumers.

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure.

Dose response and endpoint specific/severity issues

1

The starting point is a NOAEC. In this study, volunteers exposed to 100 ppm for 1 hour did not report irritation but when the exposure period was extended to 7 hours, mild and transient eye irritation was reported. There were no reports of irritation in volunteers exposed to 216 ppm for 1 hour and hence it was concluded in the UK RAR (2008) that the irritation reported by volunteers exposed to 100 ppm for 7 hours may have been due to eye dryness rather than primary irritation. At 375 ppm, 4 out of 9 volunteers reported mild eye irritation and all reported nasal irritation. These findings indicate that the dose-response relationship for irritation is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.

Quality of database

1

The quality of the database for this endpoint is adequate. A range of concentrations and exposure durations were tested in the key study. The results were internally consistent and were supported by results obtained in two separate but small scale human volunteer studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Overall assessment factor: 5

Endpoint specific DNEL: 216/5 = 43 ppm, equivalent to 182.75 mg/m3

 

 

1.2) DNEL based on systemic effects (CNS depression)

The dose descriptor is the NOAEC of 100 ppm obtained from a study with 6 human volunteers exposed for 7 hours (Stewart et al., 1968). CNS depression is a dose-dependent effect. It is therefore necessary to adjust the NOAEC by a factor of 0.67 to take account of the different doses that will be received due to differences in breathing rates between volunteers at rest and workers engaged in light activity.

100 x 0.67 = 67 ppm (7 hours)

Since the short-term inhalation DNEL has a 15 minute reference period it is also necessary to convert the 7-hour NOAEC to an equivalent dose that would be inhaled over a 15 minute period. This is done using the modified Haber’s rule cnt = k (TGD, Chapter R8, Appendix R8-8, page 108) where ‘c’ is the concentration, ‘t’ is the exposure time, ‘n’ is a regression coefficient and ‘k’ is a constant. It is not possible to determine an appropriate value for ‘n’ from the available data, therefore the default value of 3 to extrapolate from a longer to shorter exposure period will be used.

3 (673 x 7 x 4) = 203 ppm (15 minutes)

The corrected starting point is 203 ppm (15 minutes)

 

Assessment factors and DNEL calculation for consumer DNEL short-term inhalation systemic effects

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

5

There are no data to quantify variability in susceptibility to the irritant effects of styrene in the human population. For local effects by inhalation ECETOC proposes an assessment factor of 5 for intraspecies variability when starting from animal data. Taking into account that an assessment factor of 3 was used for workers this higher factor of 5 is appropriate for consumers.

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure.

Dose response and endpoint specific/severity issues

1

The starting point is a NOAEC. Minor impairments in neurobehavioural test performances were reported for volunteers exposed to concentrations of around 200 ppm for 1 hour. These data support the conclusion that 100 ppm can be regarded as a NOAEC for a 7-hour exposure and suggest that the dose-response relationship for CNS depression is not steep. A factor to take account of uncertainties in the NOAEC is therefore not justified.

Quality of database

1

The quality of the database for this endpoint is adequate. The key study is a human volunteer study the results of which show a dose-related trend for increasing severity with increasing dose. The results of the key study are supported by data from several additional human volunteer studies conducted by separate groups of researchers. This consistency provides confidence in the reliability of these studies. It is therefore not necessary to apply a factor to take account of deficiencies in the quality of the data.

Overall assessment factor: 5

Endpoint specific DNEL: 203/5 = 41 ppm, equivalent to 174.25 mg/m3

 

 

1.3) Selection of consumer-DNEL short-term inhalation

A DNEL of 43 ppm was calculated for eye and respiratory tract irritation compared to a DNEL of 41 ppm for CNS depression. CNS depression is therefore identified as the critical health effect for the risk assessment of short-term exposure.

The consumer DNEL short-term inhalation route is 40 ppm (15-minute reference period).

 

 

2) Consumer / humans via environment-DNEL long-term for inhalation route

The UK RAR (2008) concluded that long-term repeated exposure to styrene has the potential to cause effects on colour vision discrimination, ototoxicity and developmental toxicity. A dose descriptor for effects on colour vision discrimination and partly also on ototoxicity has been identified from studies on workers. The available human data relating to developmental toxicity do not provide sufficient information to allow a human dose descriptor to be identified for this endpoint. A dose descriptor for this endpoint has been identified from animal data. Since the dose-response relationship and evidence base for each endpoint is different it is not clear which is the critical endpoint for risk assessment of long-term repeated exposure. It will therefore be necessary to calculate separate endpoint specific DNELs for each effect to identify the critical long-term DNEL.

 

2.1) Consumer for DIY tasks

The consumer-DNEL long-term inhalation may be used to assess exposures during DIY tasks. These tasks may take place for varying periods of time depending on the task and may be carried out once for a small repair task or over several days for a large project such as boatbuilding. In the RAR it was suggested that individuals building their own boat may spend up to 8 hours in one day on the project. Therefore an 8-hour reference period will be used for the consumer (DIY) DNEL long-term for the inhalation route. It is assumed that an individual will spend 2 days at a time (i.e. a weekend) on the project. Similar to the considerations for the worker-DNEL long-term, humans of an age corresponding to that of animals directly after weaning (as in the rat 2-generation study) will not perform such tasks.

 

2.1.1) Endpoint specific DNEL for effects on colour vision

There is an extensive body of data in the UK RAR (2008) on the effects of exposure to styrene on colour vision discrimination obtained from studies in workers using tests specifically designed to examine this endpoint. A NOAEC of 50 ppm (8-hr TWA) was identified from studies discussed in the UK RAR and further supported by a recent investigation of Seeber et al. (2009). This dose descriptor was obtained from studies of workers. The starting point is therefore 50 ppm.

For DIY tasks the different weekly exposure schedules have to be taken into account (5 d/week for workers vs 2 d/week for consumers) by a factor of 5/2=2.5 leading to an adjusted starting point of

50 x 2.5 = 125 ppm.

 

Assessment factors and DNEL calculation for consumer (DIY) DNEL long-term inhalation for effects on colour vision

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

3

There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in consumers. Since the dose descriptor reflects findings from a number of studies covering in total hundreds of workers from several nationalities the data already addresses variability in workers and hence a factor of 3 has been selected to take account of the possible additional intraspecies variability within the consumer population. The factor of 3 corresponds to the recommendation of ECETOC (2010) for extrapolation from workers to consumers based on human data.

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.

Dose response and endpoint specific/severity issues

1

The extensive database for this endpoint encompasses a range of exposure conditions allowing information on the exposure-response relationship and severity to be obtained. The UK RAR (2008) concluded that no changes in colour vision discrimination would be expected with 8-hour TWA exposures below 20 ppm. In some of the studies before 2009 effects were reported at exposures below 50 ppm. But the exposure assessments are less reliable than those of the workforce studied by Seeeber et al. (2009) who did not find colour vision deficiencies at exposures up to 50–100 ppm. Furthermore, in all studies when slight changes were detected in tests, the effects were reversible, the individuals concerned were not aware of any deficit and there was no indication that performance was affected in jobs requiring good colour discrimination. The data at higher levels of exposure was not considered to be sufficiently robust to reliably characterise the scale and nature of the effect. On this basis and given that the effects are reversible, it is not considered necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.

Quality of database

1

Since the database for this endpoint includes rigorous and well-reported studies, it is not considered necessary to apply an assessment factor to take account of uncertainties arising from poor quality information. 

Overall assessment factor:  3

Endpoint specific DNEL: 125/3 = 42 ppm, equivalent to 178.5 mg/m3

 

 

2.1.2) Endpoint specific DNEL for ototoxicity

Studies have been conducted in workers and in laboratory animals to investigate the potential for exposure to styrene to have an adverse effect on hearing. In studies before 2009 limited evidence was obtained for styrene-induced hearing loss in workers but due to co-exposure to noise and other solvents and insufficient exposure data in these studies it was not possible to establish a clear dose-response relationship. In the study of Triebig et al. (2009) no hearing deficits were found for exposures of 12.5 ppm and 50 ppm at the time of investigation going back to about 10 years. On the other hand, there was an indication for styrene induced hearing losses in a subgroup of “high-long” exposed workers assumed to be exposed at 25-33 ppm over about 15 years (range up to 26 years). Higher exposures of 80-100 ppm existed for a time more than 10 years before this study was initiated. Taking into account the irreversibility of styrene induced hearing deficit, these effects are considered to stem from the former high exposures. In summary a NOAEC for humans of 20 ppm can be derived as starting point from this study.

For DIY tasks the different weekly exposure schedules have to be taken into account (5 d/week for workers vs. 2 d/week for consumers) by a factor of 5/2=2.5 leading to an adjusted starting point of

20 x 2.5 = 50 ppm.

There is clear evidence from studies in laboratory animals that styrene has a specific adverse effect on hearing. The effect is characterised by an elevation of hearing thresholds across particular frequencies and is the result of irreversible damage within the ear. This occurs because styrene selectively destroys hair cells in the cochlea possibly because of an effect on the membranous organisation of these cells. It is assumed that the effects seen in animals are of relevance for humans. Studies in rats have indicated that hearing loss occurs within a few days of the start of exposure and although it does not increase in severity with continued exposure, the initial effect is irreversible. A NOAEC of 500 ppm was identified in the UK RAR (2008) and this will be used as the starting point for the derivation of DNELs for ototoxicity based on animal studies (exposure schedule 6 h/d, 5 d/week). But it has to be taken into consideration that Lataye et al. (2005) did observe minor hair cell loss in the cochlea at 500 ppm.

Using animal studies to derive the DNEL it has to be taken into account that animals were exposed for 6 hour per day whereas consumers are assumed to be exposed for up to 8 hours per day, but only 2 days per week. Therefore it is necessary to adjust the starting point for consumers (DIY) by a factor of 0.75 to take account of differences in daily dose and a factor of 5/2 (2.5) for the weekly schedule. It is also necessary to adjust the starting point for consumers (DIY) by a factor of 0.67 to take account of differences in inhalation rates between animals at rest and humans involved in light activity.

The corrected starting point for animal studies is therefore:

500 ppm x 0.75 x 0.67 x 2.5 = 630 ppm (8-hours).

 

Assessment factors and DNEL calculation for consumer (DIY) DNEL long-term inhalation for ototoxicity based on animal studies

Uncertainties

AF

Justification

Interspecies differences

1

For interspecies variability the assessment factors proposed by ECETOC (2003, 2010) are used. The dose descriptor was obtained from an inhalation study and is being used to derive an inhalation DNEL. It is therefore not necessary to apply an allometric scaling factor to take account of differences in basal metabolic rates between animals and humans. According to ECETOC the additional assessment factor of 2.5 to quantify other differences between animals and humans that could affect interspecies extrapolation is scientifically not justified and a factor of 1 is appropriate. On this basis the default factor of 1 to account for other species differences will be applied.

Intraspecies differences

5

For intraspecies variability the assessment factor proposed by ECETOC (2003, 2010) is used. There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in the human population. The default factor of 5 as proposed by ECETOC will therefore be used to take account of intraspecies variability.

In total there is a combined inter- and intraspecies assessment factor of 5 that takes into account that the target tissue (outer hair cells in the cochlea, anatomical structure and blood supply of the cochlea) is identical in rats and humans.

Differences in duration of exposure

1

The dose descriptor was obtained from a 4 week study. Although the DNEL is to be used to assess long-term repeated exposure there is strong evidence showing that the ototoxic effects of styrene occur within a week of initial exposure and do not progress in severity with further exposure. On this basis, the duration of this study is adequate for the endpoint being studied and it is not necessary to apply a factor to take account of differences in duration of exposure.

Dose response and endpoint specific/severity issues

2

Several studies have been conducted in the rat to investigate ototoxicity. The studies encompass a range of concentrations and durations of exposure and provide reliable information on the dose-response relationship and severity of effect. The effect is characterised by an elevation of hearing thresholds and is the result of irreversible damage within the cochlea. In the UK RAR (2008) a NOAEC for hearing threshold of 500 ppm has been identified in the key study. But as minor histopathological alterations were found at 500 ppm an assessment factor of 2 is used. At higher exposure levels, hearing thresholds were increased and the level of increase correlated with dose. Minor shifts of 1-3 dB were reported in rats exposed to around 600 ppm increasing to threshold shifts of 35 – 40 dB at concentrations of 800 – 1000 ppm.

Quality of database

1

The findings from the key study are supported by findings from several additional studies conducted to modern regulatory standards by separate groups of researchers. On this basis the quality of the database is not considered to contribute uncertainty and it is therefore not necessary to apply an additional factor.  

Overall assessment factor:  10

Endpoint specific DNEL: 630/10 = 63 ppm (8-hours) , equivalent to 267.75 mg/m3

 

Assessment factors and DNEL calculation for consumer (DIY) DNEL long-term inhalation for ototoxicity based on human data

Uncertainties

AF

Justification

Interspecies differences

-

The starting point is obtained from human data so it is not necessary to apply a factor to take account of interspecies differences.

Intraspecies differences

3

There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in consumers. Since the dose descriptor reflects findings from a number of studies covering in total hundreds of workers from several nationalities the data already addresses variability in workers and hence a factor of 3 has been selected to take account of the possible additional intraspecies variability within the consumer population. The factor of 3 corresponds to the recommendation of ECETOC (2010) for extrapolation from workers to consumers based on human data.

Differences in duration of exposure

1

It is not necessary to apply a factor to take account of duration of exposure because the data relate to long-term workplace exposure.

Dose response and endpoint specific/severity issues

1

The database for this endpoint encompasses a range of exposure conditions allowing information on the time- and exposure-response relationship and severity to be obtained. On this basis, it is not necessary to apply an assessment factor to take account of uncertainties in the dose-response relationship.

Quality of database

1

Since the information is based on a rigorous and well-reported study, it is not necessary to apply an assessment factor to take account of uncertainties arising from poor quality information. 

Overall assessment factor:  3

Endpoint specific DNEL: 50/3 = 17 ppm, equivalent to 72.25 mg/m3

 

In conclusion, a worker DNEL long-term inhalation for ototoxicity of 17 ppm is proposed based on data obtained by a cohort study on exposed workers. This is to be considered sufficiently conservative in comparison to a DNEL derived from a large animal database, i.e. 63 ppm.

 

 

2.1.3) Endpoint specific DNEL for developmental toxicity

A NOAEC of 150 ppm has been identified for developmental toxicity in a 2 -generation reproductive toxicity study in which rats were exposed for 6 hours per day, 7 days per week (Cruzan et al., 2005a, b).

It has to be taken into consideration that the exposure scenarios for specific life stages in the 2-generation study are not relevant for derivation of a DNEL long-tem for consumers performing DIY tasks. The following exposure situations do not apply for this situation:

direct exposure of pups by inhalation for the time between weaning and puberty as occurred in F1 pups

exposure of parental animals from weaning to puberty as occurred in F1 animals producing the F2 generation.

Therefore the NOAEC must not be taken from the F2 generation, if differences exist between those of F1 and F2 offspring. Furthermore, if there are effects occurring only in F1 offspring after weaning with direct inhalation exposure, these are irrelevant for defining a consumer (DIY) DNEL. On the other hand, effects found in F1 offspring during the nursing period have to be taken into account for the human situation if in exceptional cases maternal leave is not taken.

No exposure related effects were observed in F1 offspring during the nursing period up to weaning. Therefore the highest exposure concentration of 500 ppm is taken as NOAEC. This is a conservative starting point as the “real” NOAEC is higher, but the difference between 500 ppm and the “real” NOAEC cannot be quantified.

Since animals were exposed for 6 hours per day, whereas consumers (DIY) may be exposed for up to 8 hours per day, it is necessary to adjust the starting point by a factor of 0.75. To take account of the fact that animals were exposed for 7 days whereas the consumer exposure is assumed to be on 2 days per week, the starting point will be adjusted by a factor of 7/2 (3.5) It is also necessary to adjust the starting point by a factor of 0.67 to take account of differences in inhalation rates between animals at rest and consumers undertaking light activity.

The corrected starting point is therefore:

500 ppm x 0.75 x 3.5 x 0.67 = 880 ppm (8-hours)

 

Assessment factors and DNEL calculation for consumer DNEL long-term inhalation for developmental toxicity

Uncertainties

AF

Justification

Interspecies differences

1

For interspecies variability the assessment factors proposed by ECETOC (2003, 2010) are used. The dose descriptor was obtained from an inhalation study and is being used to derive an inhalation DNEL. It is therefore not necessary to apply an allometric scaling factor to take account of differences in basal metabolic rates between animals and humans. According to ECETOC the additional assessment factor of 2.5 to quantify other differences between animals and humans that could affect interspecies extrapolation is scientifically not justified and a factor of 1 is appropriate. On this basis the default factor of 1 to account for other species differences will be applied.

Intraspecies differences

5

For intraspecies variability the assessment factor proposed by ECETOC (2003, 2010) is used. There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in the human population. The default factor of 5 as proposed by ECETOC will therefore be used to take account of intraspecies variability.

In total there is a combined inter- and intraspecies assessment factor of 5 that takes into account that the target tissue (outer hair cells in the cochlea, anatomical structure and blood supply of the cochlea) is identical in rats and humans.

Differences in duration of exposure

1

The NOAEC was derived from the 2-generation study starting from exposure of young adult animals of the F0 generation up to weaning of the F1 generation. This represents a worst case scenario for workers being exposed to styrene from the start of their working life, during pregnancy up to the end of the breast feeding period without a maternity leave. An assessment factor of 1 is therefore appropriate.

Dose response and endpoint specific/severity issues

1

As 500 ppm was a clear NOAEC for developmental effects in F1 offspring before weaning and start of direct inhalation exposure, an assessment factor is not warranted in this respect.

Quality of database

1

The key study was conducted to modern regulatory standards and was adequately reported. The findings are supported by results from other studies conducted to modern regulatory standards. On this basis the quality of the database is not considered to contribute uncertainty and it is therefore not necessary to apply an additional factor.     

Overall assessment factor:  5

Endpoint specific DNEL: 880/5 = 176 ppm (8-hour) , equivalent to 748 mg/m3

 

 

2.1.4) Selection of consumer (DIY)-DNEL long-term inhalation

The most sensitive endpoint-specific DNEL is that for ototoxicity derived from observations in workers. This endpoint is relevant for consumers (DIY).

The consumer DNEL long-term inhalation route is 17 ppm (8-hr TWA).

 

 

 

2.2) Humans via environment DNEL long-term inhalation

As discussed in section B.5.11.4 the UK RAR (2008) concluded that long-term repeated exposure to styrene has the potential to cause effects on colour vision discrimination, ototoxicity and developmental toxicity. The DNEL long-term inhalation via environment will be based on the consumer (DIY) DNEL long-term inhalation for colour vision and ototoxicity. For the continuous exposure via the environment the different exposure scenarios have to be taken into account:

8 h/d for DIY vs. 24 h/d for exposure via the environment: 8/24

2 d/week for DIY vs. 7 d/week for exposure via the environment: 2/7

In addition, the worker DNEL is derived for light physical activity at the workplace. This does not apply to the continuous exposure via the environment leading to a correction factor of 1/0.67.

 

Starting from the consumer (DIY) DNEL for effects on colour vision of 42 ppm the DNEL long-term inhalation via environment will be:

42 x 2/7 x 8/24 x 1/0.67 = 6.0 ppm, equivalent to 25.5 mg/m3.

 

Starting from the consumer (DIY) DNEL for ototoxicity of 17 ppm (based on human data) the DNEL long-term inhalation via environment will be:

17 x 2/7 x 8/24 x 1/0.67 = 2.4 ppm, equivalent to 10.2 mg/m3.

 

For derivation of a consumer (DIY) DNEL long-term based on reproductive effects in the 2-generation rat study, effects observed in the F2 generation and in the F1 generation for the time between weaning and puberty did not apply. On the other hand, effects occurring during all phases of the 2-generation study have to be taken into account for exposures via the environment. In the UK RAR a NOAEC of 150 ppm has been identified for developmental toxicity in the 2-generation reproductive toxicity study in which rats were exposed for 6 hours per day, 7 days per week. Since animals were exposed for 6 hours per day, whereas the exposure via the environment is continuous, it is necessary to adjust the starting point by a factor of 6/24. A correction for physical activity is not necessary and the corrected starting point is therefore

150 x 6/24 = 37.5 ppm.

 

Assessment factors and DNEL calculation for DNEL long-term inhalation via the environment for reproductive effects

Uncertainties

AF

Justification

Interspecies differences

1

For interspecies variability the assessment factors proposed by ECETOC (2003, 2010) are used. The dose descriptor was obtained from an inhalation study and is being used to derive an inhalation DNEL. It is therefore not necessary to apply an allometric scaling factor to take account of differences in basal metabolic rates between animals and humans. According to ECETOC the additional assessment factor of 2.5 to quantify other differences between animals and humans that could affect interspecies extrapolation is scientifically not justified and a factor of 1 is appropriate. On this basis the default factor of 1 to account for other species differences will be applied.

Intraspecies differences

5

For intraspecies variability the assessment factor proposed by ECETOC (2003, 2010) is used for the general population. There are no data to quantify variability in susceptibility to the effects of long-term exposure to styrene in the human population. The default factor of 5 for the general population as proposed by ECETOC will therefore be used to take account of intraspecies variability.

Differences in duration of exposure

1

The NOAEC was derived from the 2-generation study covering the whole reproductive cycle. An assessment factor of 1 is therefore appropriate.

Dose response and endpoint specific/severity issues

2

At the NOAEC of 150 ppm there was a minor decrease (up to 10%) in pre-weaning body weight only in F2 generation rats. This was not considered sufficient to warrant lowering the NOAEC but a factor of 2 is applied to take account of this.

Quality of database

1

The key study was conducted to modern regulatory standards and was adequately reported. The findings are supported by results from other studies conducted to modern regulatory standards. On this basis the quality of the database is not considered to contribute uncertainty and it is therefore not necessary to apply an additional factor.     

Overall assessment factor:  10

Endpoint specific DNEL: 37.5/10 = 3.7 ppm , equivalent to 15.725 mg/m3

 

 

2.2.1) Selection of DNEL long-term inhalation via the environment

The most sensitive endpoint-specific DNEL is that for ototoxicity derived from observations in workers. This endpoint is relevant for exposure via environment.

The DNEL long-term inhalation route via environment is 2.4 ppm.

 

 

3.3.) Consumer-DNEL long-term for dermal route for DIY tasks

The consumer (DIY) DNEL long-term for the dermal route is related to the same exposure scenario for DIY tasks as described in section B.5.11.7.1 for the consumer (DIY) DNEL long-term inhalation, i.e. 8 h/day, 2 days/week at the weekend. A continuous exposure for consumers or humans via the environment by the dermal route does not exist.

The lowest consumer (DIY) DNEL long-term inhalation (section B.5.11.7) based on ototoxicity in workers was calculated to be 17 ppm, corresponding to 73 mg/m³. Using for consumers performing DIY tasks under light physical activity a respiratory volume of 10 m³/person/day and a body weight of 70 kg (ECHA, 2008) the external exposure would be 73 x 10/70 = 10.4 mg/kg/d.

It is necessary to convert this inhalative dose to an equivalent dermal dose. The UK RAR (2008) concluded that there is 100 % absorption of styrene from the respiratory tract but in humans only 2 % of a dermal dose of liquid styrene is likely to be absorbed. The corrected dermal NOAEL therefore would be:

10.4 x 100/2 = 521 mg/kg/day

ECHA (2008) proposes to take a limited absorption rate for the starting route, leading to a low (conservative) internal NOAEL. Engström et al. (1978a) investigated the uptake of styrene in 7 volunteers at 50 ppm at rest and under physical activity (50 - 150 Watt). Under light activity (50 Watt) the uptake was 66%. If this absorption is taken into account a corrected dermal NOAEL of

10.4 x 66/2 = 343 mg/kg/d is obtained.

Since the consumer (DIY) DNEL long-term for dermal exposure was directly derived from that for inhalation exposure no further assessment factors are necessary.

The consumer (DIY) DNEL long-term dermal route for systemic effects is 343 mg/kg/day.

This DNEL does not address the potential for local irritation. The risk characterisation will consider whether specific risk management measures are necessary to protect against local effects.

This DNEL does not address the potential for local irritation. The risk characterisation will consider whether specific risk management measures are necessary to protect against local effects.

 

3.4) Humans via environment DNEL long-term oral route

The lowest DNEL long-term for the inhalation route via environment was calculated to be 2.4 ppm, corresponding to 10.2 mg/m³. A respiratory volume of 20 m³/person/d is used for humans exposed via environment (ECHA, 2008) and an uptake by inhalation of 70% according to Engström (1978a). This leads to an internal body burden of

10.3 x 20 x 0.7 = 144 mg/person/d, corresponding to 2.1 mg/kg/d.

The oral absorption in rats is 90% and therefore 100% absorption by oral exposure is taken for humans.

Thus, the DNEL long-term oral is 2.1 mg/kg/d for humans exposed via environment.

A slightly different approach was used by Gelbke et al. (2014) based on a comprehensive assessment of the original NOAELs/LOAELs obtained in studies with humans and animalsand applying the assessment factors proposed by European organisations (EFSA, ECHA, ECETOC). Ototoxicity and developmental toxicity in rats and human ototoxicity and effects on colour discrimination have been identified as the most relevant toxicological properties for styrene health assessments. Safe exposure levels derived from animal studies with assessment factors of EFSA and ECHA were expectedly much lower than those using the ECETOC approach. Comparable safe exposure levels were obtained from human data with all sets of assessment factors while ototoxicity in rats led to major differences, especially for different routes of exposure. The safe exposure levels finally selected based on criteria of science and health protection converged to the range of 90–120 mg/person/d corresponding to 1.3-1.7 mg/kg bw/d based on 70 kg body weight. These safe exposure limits are slightly lower than the DNEL long-term, oral derived here.