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Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
208 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
1
Modified dose descriptor starting point:
NOAEC
Acute/short term exposure
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
208 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
1
Acute/short term exposure
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information
Overall assessment factor (AF):
1

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
13.67 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
12
Modified dose descriptor starting point:
NOAEL
Acute/short term exposure
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1.5 mg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1.5 mg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10

Workers - Hazard for the eyes

Additional information - workers

Since MMA is of low acute toxicity with the median lethal dose values (LD50) being significantly greater than 2000 mg/kg by oral and dermal routes and above 5000 ppm (20800 mg/m³) by inhalation, with the exeption of the acute dermal DNEL the oral and inhalation DNELs derived for long-term exposure are considered sufficiently protective of acute exposure.

Acute, short-term exposure - local effects - dermal:

In addition, an induction-specific DNEL was derived for skin sensitization based on the EC3 value from a LLNA study (Betts et al., 2006). The sensitisation threshold (EC3 value) was reported to be 60% w/v, indicative of a sensitiser of moderate potency. According to the Guidance on information requirements and chemical safety assessment, Chapter R.8, the EC3 value (in mg/cm²) can be used as a surrogate for the NOAEL for induction. EC3 data generally correlate well with human skin sensitisation thresholds. However, there are cases where this correlation is poor and the two values may differ by 10-fold or more. Therefore, using the default AF of 10 for interspecies variation, the acute dermal DNEL was calculated to be 1.5 mg/cm²/day.

 

Acute, short-term exposure - local effects - inhalation:

Calculation from the weight-of-evidence review of the inhalation toxicity of MMA performed by SCOEL:

The critical effect identified by SCOEL was focal lesion of the olfactory region of the nasal epithelium in both rats and mice following repeated exposure as a consequence of local metabolism of MMA to methacrylic acid by carboxylesterases in the nasal epithelial cells. For defining the “critical inhalation exposure level at the workplace” a reliable NOAEC of 25 ppm and LOAEC of 100ppm was available from a 2-year inhalation study in rats. SCOEL judged that “extensive” PBPK modelling work predicted that on kinetic grounds, for a given level of exposure to MMA, human nasal olfactory epithelium will be at least 3 times less sensitive than that of rats to the toxicity of MMA. SCOEL also judged that the available studies of workforces provided reassuring evidence that workers exposed to MMA levels of up to approximately 50 ppm (8-hr TWA) have not suffered any respiratory ill-health consequences related to their long-term exposure with the occasional respiratory symptoms reported seem to be clearly connected with short-term peak exposures and the sensory irritant potential of MMA which starts to be expressed at concentrations somewhere in excess of 100 ppm. SCOEL concluded further that ‘While there are no data to clearly indicate the threshold concentration above which such irritancy begins to be expressed in humans … irritant concentrations clearly lie above 100 ppm. Hence a STEL of 100 ppm is recommended’.

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

416 mg/m³
(100 ppm)

NOAEC in workers (SCOEL)

Step 2) Modification of starting point

1

As the human effects data were long term, full-shift duration, worker-health studies no adjustment factors were considered necessary.

Step 3) Assessment factors

 

 

Interspecies

1

8h-NOAEC of approximately 50 ppm and 8h-LOAEC “somewhere in excess” of 100 ppm for occupationally exposed workers. No adjustment is required.

Intraspecies

1

The key studies were in large groups of workers.

Exposure duration

1

The key studies were worker health studies on workforces with long employment histories (in excess of 25 yrs in some cases) and full shift (8-hr) work activities. No adjustment is required.

Dose response

1

The NOAEC is reliable. No adjustment is required.

Quality of database

1

The key studies were of high quality, being rated K1. No adjustment is required.

DNEL

Value

based on SCOEL STEL of 100 ppm

 

Using a total factor (POD modifier and AF) of 1 a DNELlong-term, workerof 416 mg/m³ (100 ppm) is derived.

 

Long-term exposure (inhalation) - local effects

Animal data:

Extensive repeated dose studies have been reported on the inhalation toxicity of MMA. For local effects, the most appropriate value is the NOEL of 25 ppm (102.5 mg/m³) in rats exposed to MMA for 2 years (Rohm & Haas, 1979).  Effects at the next higher concentration (100 ppm; 410 mg/m³) were degenerative changes in the olfactory epithelium. The pattern of the critical effects of inhalation of MMA in animal studies (i. e. the olfactory epithelium being affected at lowest concentration) is consistent with toxicity resulting from metabolism of the inhaled material in the olfactory tissue by carboxylic esterases to methacrylic acid. Based on limited data from human tissue samples (that may not have been morphologically normal taken at polyp biopsy), the activity of alpha-naphthylbutyrate carboxylesterase in human nasal respiratory tissue is less than that in the rat (Mattes & Mattes, 1992). In addition, rodents are obligate nose breathers, whereas humans can also breathe through their mouths, which is expected to reduce exposure of the nasal epithelium. There are also differing nasal flow patterns, with the greater airflow across the human olfactory epithelium during the expiratory phase when the vapour concentration would be considerably reduced as a result of absorption in the lower respiratory tract. Furthermore, there are significant morphological differences between species in the structure of the nasal cavity, which result in differences in concentrations of inhaled materials at the nasal tissue.  These are reflected in differences in surface area normalized to minute ventilation, being fivefold greater in rodents than in humans (DeSesso, 1993).  A much greater percentage of the nasal cavity is lined by olfactory epithelium in rats than in humans.

Therefore, the extrapolation of data on nasal irritation of the olfactory epithelium observed in rodents in local DNEL derivation for humans is considered to be inapplicable and exposure related observations in humans were used for the derivation of the DNEL for workers by long-term inhalation.

Human data:

Records of 211 workers from an acrylic sheet production plant almost exclusively exposed to MMA for an average of 8.8 years at 8-hour average concentrations of up to 40 ppm (160 mg/m³) did not show any symptoms of a MMA exposure related rhinopathy or any signs of MMA related abnormalities in the nasal cavity (Röhm 1994; Muttray et al. 1997). Local irritations occurred only at short term peak exposures at concentrations > 100 ppm (420 mg/m³). Based on these data, the national occupational exposure limit (OEL) for MMA inhas been set to 50 ppm (210 mg/m³).

 

SCOEL reviewed MMA after the EU-ESR and established a health-based occupational exposure limit (SCOEL, 2005). The critical effect identified by SCOEL was focal lesion of the olfactory region of the nasal epithelium in both rats and mice following repeated exposure as a consequence of local metabolism of MMA to methacrylic acid by carboxylesterases in the nasal epithelial cells. For defining the “critical inhalation exposure level at the workplace” a reliable NOAEC of 25 ppm and LOAEC of 100ppm was available from a 2-year inhalation study in rats. SCOEL judged that “extensive” PBPK modelling work predicted that on kinetic grounds, for a given level of exposure to MMA, human nasal olfactory epithelium will be at least 3 times less sensitive than that of rats to the toxicity of MMA. SCOEL also judged that the available studies of workforces provided reassuring evidence that workers exposed to MMA levels of up to approximately 50 ppm (8-hr TWA) have not suffered any respiratory ill-health consequences related to their long-term exposure with the occasional respiratory symptoms reported seem to be clearly connected with short-term peak exposures and the sensory irritant potential of MMA which starts to be expressed at concentrations somewhere in excess of 100 ppm.

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

208 mg/m3(50 ppm)

NOAEC in workers (SCOEL)

Step 2) Modification of starting point

1

As the human effects data were long term, full-shift duration, worker-health studies no adjustment factors were considered necessary.

Step 3) Assessment factors

 

 

Interspecies

1

NOAEC ofapproximately 50 ppmand LOAEC “somewhere in excess” of 100 ppm for occupationally exposedworkers.No adjustment is required.

Intraspecies

1

The key studies were in large groups of workers.

Exposure duration

1

The key studies were worker health studies on workforces with long employment histories (in excess of 25 yrs in some cases) and full shift(8-hr) work activities.No adjustment is required.

Dose response

1

The NOAEC is reliable. No adjustment is required.

Quality of database

1

The key studies were of high quality, being rated K1.No adjustment is required.

DNEL

Value

based on SCOEL IOLV of 50 ppm (8-h TWA) and STEL of 100 ppm.

 

Using a total AF of 1 a DNELlong-term,workerof 208 mg/m3(50 ppm) is derived.

 

Long-term exposure (inhalation) - systemic effects

SCOEL in its review on MMA placed greater emphasis on the local effect in the nasal passges although they did recognise no long term adverse systemic health effects in workers occupationally exposed for many years. In order to verify that this approach was sufficiently protective for systemic effects a long term systemic DNEL has been derived from the available animal data.

During the ESR for methyl methacrylate the observation of reduced body weight gain in repeat dose inhalation studies was discussed and in the absence of definitive food consumption data in these studies it could not be concluded that this effect was a consequence of the local irritation and reduced feeding and was therefore considered a substance-related systemic finding. Subsequent to the completion of the ESR two studies were conducted; a 90 d repeat dose inhalation study with MAA and a 2-generation study with MMA. In which reduced body weight gain effects were observed in both studies and concurrent food and drinking consumption data clearly demonstrated that this effect was not general systemic toxicity.

 

In the repeated dose section the point of departure for the derivation of the repeat-dose, systemic, DNEL for inhalation was identified as the observation of general toxicity and increasing lethality at 2000 ppm and above in a 14 week inhalation study in rats (Battelle, 1980). The highest no-effect-concentration observed in the 2-year inhalation studies was 500ppm (NTP, 1986).

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

2080 mg/m3(500 ppm)

NOAEC in 6h/day, 5days/week 2 yr inhalation study in rats (NTP, 1986)

Step 2) Modification of starting point

8/6

 

 

10 m3/6.7 m3

Correction of exposure duration in rats (6 hrs/day) to default worker exposure (8 hrs/day) is required.

-Correction for activity driven differences of respiratory volumes in workers compared to workers in rest (10 m3/6.7 m3) is required (ECHA 2008).

Step 3) Assessment factors

 

 

Interspecies

1

No allometric scaling rat to humans as inhalation (ECHA 2008).

Due to the known metabolism of MMA via general metabolic pathways that are common and very similar to rodents and humans and the absence of any specific target organs indicating a specific MOA at high concentrations there is no reason to believe that an additional AF of 2.5 for remaining differences not justified..

Intraspecies

3

Standard metabolism involving ubiquitous and general metabolic pathways (ester hydrolysis followed by TCA) makes a lower variability likely, hence the AF of 3 by ECETOC (2010) is sufficiently conservative.

Exposure duration

1

The key study is a two year inhalation study in rats.No adjustment is required.

Dose response

1

The NOAEC is reliable. No adjustment is required.

Quality of database

1

The key study is of high quality, being rated K1.No adjustment is required.

DNEL

Value

Based on NOAEC of 2080 mg/m3(500 ppm) in 6h/day, 5days/week 2 yr inhalation study in rats (NTP, 1986).

Using a total factor of 5.97 (8/6 x 10/6.7 x 3) a DNELlong-term,workerof 348.4mg/m3(83.75 ppm) is derived.

 

The derived DNELlong-term,workerof 348.4mg/m3 (83.75 ppm) for systemic effects is higher than the DNELlong-term,workerof 208 mg/m3 (50 ppm) for local effects and therefore the DNEL for local effects is protective for systemic effects. This value is carried forward to the risk assessment.

 

Long-term exposure (oral/dermal exposure) - systemic effects

 

The most relevant point of departure for the oral/dermal DNEL was identified in a 2-year repeat-dose oral (drinking water) exposure study with MMA in which the NOAEL was 164 mg/kg bw/day (2,000 ppm in drinking water) (Borzelleca et al, 1964).

Description

Value

Remark

Step 1) Relevant dose-descriptor

NOAEL:
2000 ppm in drinking water

NOAEL for rats (7 days/week) for 2 years

Step 2) Modification of starting point

164 mg/kg bw/day

Conversion to food equivalent using water consumption data

Step 3) Assessment factors

 

 

Interspecies

4

Allometric scaling rat to humans AF 4 (ECHA 2008).
An extra AF of 2.5 for additional toxicodynamic differences was not applied, as dermal absorption of MMA in humans is significantly lower than in rats (Jones, 2002)

Intraspecies

3

Known mode of action involving ubiquitous and non-specific enzyme systems (carboxylesterases) makes a lower variability likely, hence the AF of 3 by ECETOC (2010) is sufficiently conservative.

Exposure duration

1

The NOAEL is based on a 2-year study

Dose response

1

 

Quality of database

1

Database of high quality.

DNEL

Value

based on NOAELrat of2000 ppm in drinking water = 164 mg/kg bw/day

Using a total AF of 12 ( 4 x 3 x 1 x 1) a DNELlong-term,workerof 13.67 mg/kg bw/d is derived.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
74.3 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
28
Acute/short term exposure
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
104 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
2
Acute/short term exposure
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information
Overall assessment factor (AF):
2

General Population - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
8.2 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
20
Modified dose descriptor starting point:
NOAEL
Acute/short term exposure
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1.5 mg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1.5 mg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
exposure based waiving
Acute/short term exposure
Hazard assessment conclusion:
exposure based waiving
DNEL related information

General Population - Hazard for the eyes

Additional information - General Population

The general points of departure are the same as for workers. Therefore, for a more detailed discussion please refer to the workers part for a specific discussion of the rationale for the particular endpoints.

The details of the calculations with the consumer-specific assessment factors are detailed in the tables below. The points of departure for the consumer assessment deviate from the worker assessment in one point: For the chronic inhalation exposure, the DNEL derived for systemi effects from the chronic inhalation studies (NTP, 1986) is lower than the DNEL for local effects derived from the IOLV by SCOEL. Therefore, the lower DNEL has been carried forward for the risk assessment.

Acute, short-term and long-term exposure - local dermal effects:

In addition, an induction-specific DNEL was derived for skin sensitization based on the EC3 value from a LLNA study (Betts et al., 2006). The sensitisation threshold (EC3 value) was reported to be 60% w/v, indicative of a sensitiser of moderate potency. According to the Guidance on information requirements and chemical safety assessment, Chapter R.8, the EC3 value (in mg/cm²) can be used as a surrogate for the NOAEL for induction. EC3 data generally correlate well with human skin sensitisation thresholds. However, there are cases where this correlation is poor and the two values may differ by 10 -fold or more. Therefore, using the default AF of 10 for interspecies variation, the acute dermal DNEL was calculated to be 1.5 mg/cm²/day.

Long-term exposure - systemic effects - dermal

In a 2-year repeat oral (drinking water) exposure study with MMA the NOAEL was 164 mg/kg bw/day (2,000 ppm in drinking water) (Borzelleca et al, 1964). In the absence of a comparable dermal study this study is used as the departure point for long-term dermal exposure.

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

NOAEL:
2000 ppm in drinking water

NOAEL for rats (7 days/week) for 2 years

Step 2) Modification of starting point

164 mg/kg bw/day

Conversion to food equivalent using water consumption data

Step 3) Assessment factors

 

 

Interspecies

4

Allometric scaling rat to humans AF 4 (ECHA 2008).
An extra AF of 2.5 for additional toxicodynamic differences was not applied, as dermal absorption of MMA in humans is significantly lower than in rats (Jones, 2002)

Intraspecies

5

Known mode of action involving ubiquitous and non-specific enzyme systems (carboxylesterases) makes a lower variability likely, hence the AF of 5 by ECETOC (2010) is sufficiently conservative.

Exposure duration

1

The NOAEL is based on a 2-year study

Dose response

1

 

Quality of database

1

Database of high quality.

DNEL

Value

based on NOAELrat of2000 ppm in drinking water = 164 mg/kg bw/day

Using a total AF of 20 ( 4 x 5 x 1 x 1) a DNELlong-term,general_populationof 8.2 mg/kg bw/d is derived.

 

Long-term exposure - systemic effects - inhalation

In the repeated dose section the point of departure for the derivation of the repeat-dose, systemic, DNEL for inhalation was identified as the observation of general toxicity and increasing lethality at 2000 ppm and above in a 14 week inhalation study in rats (Battelle, 1980). The highest no-effect-concentration observed in the 2-year inhalation studies was 500ppm (NTP, 1986).

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

2080 mg/m3(500 ppm)

NOAEC in 6h/day, 5days/week 2 yr inhalation study in rats (NTP, 1986)

Step 2) Modification of starting point

24/6

 

 

7/5

Correction of exposure duration in rats (6 hrs/day) to default general population exposure (24 hrs/day) is required.

Correction for experimental exposure of 5 days to 7 days for general population

Step 3) Assessment factors

 

 

Interspecies

1

No allometric scaling rat to humans as inhalation (ECHA 2008).

Due to the known metabolism of MMA via general metabolic pathways that are common to rodents and humans and the absence of any specific target organs indicating a specific MOA at high concentrations there is no reason to believe that an additional AF of 2.5 for remaining differences is necessary.

Intraspecies

5

Standard metabolism involving ubiquitous and general metabolic pathways (ester hydrolysis followed by TCA) makes a lower variability likely, hence the AF of 5 by ECETOC (2010) is sufficiently conservative.

Exposure duration

1

The key study was a 2 yr inhalation study in rats. No adjustment is required.

Dose response

1

The NOAEC is reliable. No adjustment is required.

Quality of database

1

The key studies were of high quality, being rated K1.No adjustment is required.

DNEL

Value

Based on NOAEC of 2080 mg/m3(500 ppm) in 6h/day, 5days/week 2 yr inhalation study in rats (NTP, 1986).

Using a total factor of 28 (24 / 6 x 7 / 5 x 5) a DNELlong-term,general populationof 74.3 mg/m3(17.9 ppm) is derived.

 

Long-term exposure - local effects - inhalation

The critical effect identified by SCOEL was focal lesion of the olfactory region of the nasal epithelium in both rats and mice following repeated exposure as a consequence of local metabolism of MMA to methacrylic acid by carboxylesterases in the nasal epithelial cells. For defining the “critical inhalation exposure level at the workplace” a reliable NOAEC of 25 ppm and LOAEC of 100ppm was available from a 2-year inhalation study in rats. SCOEL judged that “extensive” PBPK modelling work predicted that on kinetic grounds, for a given level of exposure to MMA, human nasal olfactory epithelium will be at least 3 times less sensitive than that of rats to the toxicity of MMA. SCOEL also judged that the available studies of workforces provided reassuring evidence that workers exposed to MMA levels of up to approximately 50 ppm (8-hr TWA) have not suffered any respiratory ill-health consequences related to their long-term exposure with the occasional respiratory symptoms reported seem to be clearly connected with short-term peak exposures and the sensory irritant potential of MMA which starts to be expressed at concentrations somewhere in excess of 100 ppm.

NOAECworker = 50ppm 8hr TWA

 

Description

Value

Remark

Step 1) Relevant dose-descriptor

208 mg/m3(50 ppm)

NOAEC in workers (SCOEL)

Step 2) Modification of starting point

1


 

 

 

 

 

- As demonstrated with MMA the olfactory lesion is present within 6 hrs of exposure and no increase in sensitivity exists with longer exposure. Hence no correction of exposure duration in workers (8 hrs/day) to default general population exposure (24 hrs/day) is required.

-Correction for activity driven differences of respiratory volumes in workers compared to workers in rest (10 m3/6.7 m3) is not required (ECETOC 2008).

Step 3) Assessment factors

 

 

Interspecies

1

NOAEC ofapproximately 50 ppmand LOAEC “somewhere in excess” of 100 ppm for occupationally exposedworkers.No adjustment is required.

Intraspecies

2

Default AF for extrapolation from workers to general population (ECHA 2008).

Exposure duration

1

The key studies were worker health studies on workforces with long employment histories (in excess of 25 yrs in some cases) and full shift(8-hr) work activities.No adjustment is required.

Dose response

1

The NOAEC is reliable. No adjustment is required.

Quality of database

1

The key studies were of high quality, being rated K1.No adjustment is required.

DNEL

Value

Based on SCOEL IOLV of 50 ppm (8-h TWA) and STEL of 100 ppm.

 

Using a total AF of 2 a DNELlong-term,general populationof 104 mg/m3(25 ppm) is derived.