Registration Dossier

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
2 072 mg/m³
Most sensitive endpoint:
neurotoxicity
DNEL related information
Overall assessment factor (AF):
5
Modified dose descriptor starting point:
NOAEC
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
2 072 mg/m³
Most sensitive endpoint:
neurotoxicity
DNEL related information
Overall assessment factor (AF):
5
Modified dose descriptor starting point:
NOAEC

Local effects

Acute/short term exposure
DNEL related information

Workers - Hazard via dermal route

Systemic effects

Acute/short term exposure
DNEL related information

Workers - Hazard for the eyes

Additional information - workers

This is a volatile substance and potential worker exposure would likely occur via the inhalation route. Therefore, no oral or dermal route DNELs were derived. No local effects were observed in acute or repeated exposure studies; therefore no DNEL for local effects was derived.

 

Justification for DN(ML) derivation/applied assessment factors – acute/short-term exposure – systemic effects

 

Potential worker exposure to the test substance would likely occur via only the inhalation route.The test substance 4-hr LC50 is 114428 mg/m3 in rats. The test substance does not produce toxicity via the dermal or oral routes, is not a skin or eye irritant and is not a dermal sensitizer. During non-lethal, high concentration inhalation exposures, test substance toxicity was associated with transient central nervous systems (CNS) effects, which appeared early in the inhalation exposure. The effects included transient convulsions, similar to those observed during evaluation of test substance repeated inhalation toxicity. At concentrations below the threshold for CNS effects, no adverse effects were observed. 

 

Step 1)

Description: Relevant dose-descriptor

Value: NOAEL: 15463 mg/m3

Remark: The rat 4-hr LC50 was 114428 mg/m3, but at concentrations of 25772 mg/m3and higher, central nervous system effects were seen in acute inhalation studies. No adverse effects were observed in any study at an exposure concentration of 15463 mg/m3.

 

Step 2)

Description: Modification of starting point for differences in respiratory volumes

Value: 0.67

Remark: A modification was applied to account for the increased respiratory volumes in active workers as compared to individuals at rest per REACH guidance R.8.4.2.

 

Description: Modification of starting point for worker exposure time

Value: 1

Remark: No modification of starting point is needed to correct for the worker exposure period as compared to the exposure periods used in the toxicity studies. The acute effects appeared very early in all of the inhalation exposures (within 1 hour). There was no increase in incidence or severity with increased exposure time, e.g. the toxicity was not progressive with time. Protecting the workers from the early occurring effects is the important aspect of establishing worker safe exposure levels. Adjustment for exposure time is appropriate for substances which exhibit toxicity in a concentration x time manner or if there is an expectation that more serious adverse effects may appear with increasing exposure time. According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. The data presented in the DNEL derivation section above provide a basis for the justification that the adverse effects do not increase in severity or onset with increased exposure time. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in the repeated inhalation and subchronic inhalation scenarios, indicating that adverse effects are not progressive, and that it is the exposure concentration, not the exposure duration that determines toxicological outcome. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3, and a LAEL of approximately 20618 mg/m3.  These NAEL and LAEL values would be applicable to both acute and subchronic exposures. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

 

Step 3)

Description: Assessment factor ─ Route of exposure

Value: 1

Remark: This is an inhalation -to-inhalation DNEL. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Allometric)

Value: 1

Remark: The exposure of interest is inhalation. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Other)

Value: 1

Remark:The “other interspecies” assessment factor is a composite of kinetic and dynamic factors. ECHA guidance document R.8.4.3.1 distinguishes between toxicity endpoints (effects) that are a function of direct chemical effects, and those endpoints that are associated with metabolite formation (e.g., where toxicity is a function of area-under-the-curve (AUC)). The test substance-specific data demonstrate that the adverse health effects of concern are a function of concentration, not AUC. In this respect, test substance toxicity is similar to direct contact toxicity substances where the adverse effects are a function of the physical chemical properties (e.g. pH, solubility, etc.). In such cases, the effects would be expected to behave in a qualitatively and quantitatively similar manner across laboratory animal species and humans. There was evidence of this in the test substance tests involving rats and dogs, where there was consistency in the NAELs (no-adverse-effect-levels) and LAELs (low-adverse-effect-levels). This behaviour has led researches for several decades to use rats and dogs as valuable models for screening substances for anaesthetic properties in humans. While the arguments presented in the section support using something lower than the default value of 2.5, those arguments alone are not adequate to support reducing the assessment factor to 1. The basis for the use of an assessment factor of 1 relied on the arguments/data above, and the fact that inter- and intraspecies variability are not independent variables. In our dossier, we used the default assessment factor value of 5 for the intraspecies assessment factors. For the types of non-AUC effects observed with the test substance, we viewed the default intraspecies value of 5 the worker as overly conservative. However, we decided to use the large intraspecies default assessment factor value, and reduce the “other interspecies” assessment value to arrive at an overall inter-/intraspecies assessment factor that would be appropriate for the type adverse effect observed during the robust testing of the test substance. If we had used the default interspecies assessment factor of 2.5, then we would have reduced the intraspecies assessment factor to 3 for the worker. The end result would have been essentially the same as the approach we used where we applied an “other interspecies” assessment factor of 1 and intraspecies assessment factor of 5.

 

Description: Assessment factor ─ Intraspecies

Value: 5

Remark: Default assessment factor for workers per REACH Guidance R.8.4.3.1. The selection of this value is highly conservative for the specific type of toxicity observed with the test substance. However, the basis for selection of such a high value is described in the interspecies assessment factor remarks above.

 

Description: Assessment factor – Exposure duration

Value: 1

Remark: According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. In order to ensure that our modification of the default assessment factor was consistent with ECHA guidance, we focused on 4 key characteristics: (1) the effect (transient CNS), (2) the NAELs in very short vs. subchronic exposures, (3) the likelihood of the test substance having a high bioresidence time and (4) AUC (area under the dose curve) or peak concentration relationship with CNS effects. The adverse effect associated with test substance inhalation is a transient CNS effect, and that is the effect of primary interest/concern for human health. As demonstrated by a robust dataset with exposures ranging from single 2-hr exposures to subchronic 6 hr/day exposures, the NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3 are applicable to all exposures, regardless of duration.  In other words, these NAEL and LAEL values were applicable to acute and subchronic exposures, and would be expected to apply to an extended (chronic) exposure. Further, the absence of adverse systemic toxicity or increased severity of the transient CNS effects with increasing exposure duration supports the position that the test substance does not have a high bioresidence time. Finally, the transient CNS effects have been demonstrated to occur as a function of concentration, and not as a function of AUC. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Description: Assessment factor – Dose response

Value: 1

Remark: The dose-descriptor is a no-adverse-effect-level, and the robust database supports the confidence in the dose- descriptor

 

Description: Assessment factor – Quality of database

Value: 1

Remark: A high quality, robust toxicity database exists for this substance.

 

Description: DNEL worker: acute/short-term exposure systemic effects- inhalation

Value: 2072 mg/m3

 Remark: 15463 x 0.67 /(1 x 1 x 1 x 5 x 1 x 1 x 1) = 2072 mg/m3

 

 

Justification for DN(ML) derivation/applied assessment factors – long-term exposure – systemic effects

 

Potential worker exposure to the test substance would likely occur via only the inhalation route.The test substance 4-hr LC50 is 114428 mg/m3 in rats. The test substance does not produce toxicity via the dermal or oral routes, is not a skin or eye irritant and is not a dermal sensitizer. The test substance does not present genetic, pre-natal developmental or reproductive toxicity concerns, and no systemic/organ damage was observed in subchronic inhalation toxicity studies. During non-lethal, high concentration inhalation exposures, test substance toxicity was associated with transient central nervous systems (CNS) effects, which appeared early in the inhalation exposure. The effects included transient convulsions, similar to those observed during evaluation of various substances with potential anaesthetic. At concentrations below the threshold for CNS effects, no adverse effects were observed. 

 

The qualitatively and quantitatively consistent presentation of a single toxicological effect (transient CNS effects) across all studies, regardless of exposure duration, provided a unique opportunity to clearly identify the health effect of highest concern, and an exposure threshold for the occurrence of the effects. This was accomplished by the conduct of robust, special studies using test substance exposure concentrations spanning those used in repeated exposure and subchronic studies. Details of the testing approach and relevant outcomes are provided in the following segments.

  • The initial testing plan was fairly standard, and included a phased approach where testing starting with acute toxicity, eye/skin irritation, sensitisation and in vitro genetic toxicity tests.  Following the initial phase, pre-natal developmental, subchronic, in vivo genetic and reproductive toxicity tests were conducted. Evaluation of the available data, led to the conduct of follow-on special studies specifically designed to enhance hazard data for use in human safety and risk assessment activities.
  • Rats were exposed for 4 hours in the 4-hr LC50 test (IUCLID5 entry DI.K1.4Hr.InhVap.R.HLO-626-96.KD). Design concentrations were 51544, 103088 and 206176 mg/m3 (5000, 10000 and 20000 ppm, respectively). CNS effects occurred at all concentrations. 
  • Rats were exposed 6 hr/day for 2 days in the in vivo micronucleus test (IUCLID5 entry DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD). Concentrations were 20618, 36081 and 72162 mg/m3 (2000, 3500, 7000 ppm, respectively). No adverse effects at 20681 mg/m3. CNS effects at 36081 mg/m3 and higher. 
  • Rats were exposed 6 hr/day, 7 day/wk for 10 days in the developmental toxicity test (IUCLID5 entry DI.K1.InhVap.DEV.R.HLR-255-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Rats were exposed 6 hr/day, 5 day/wk for 13 weeks in the OECD 413 90-day subchronic toxicity test (IUCLID5 entry DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Male rats were exposed 6 hr/day, 5 day/wk for 10 weeks, followed by 6 hr/day, 7 day/wk for 5 weeks, and females exposed 6 hr/day, 5 day/wk for approximately 10 weeks, followed by 6 hr/day, 7 day/wk for approximately 7 weeks in the OECD 415 reproductive toxicity test (IUCLID5 entry DI.K1.InhVap.1Gen.R.D-20699.KD). This study represented the longest exposure duration of any of the test substance studies. The exposure concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 20618 mg/m3 and lower. CNS effects at 36081 mg/m3.
  • Rats were exposed for 2 hours in a neurotoxicity test (IUCLID5 entry DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). The exposure concentrations were 10309, 20618, 30926, 41236, 51544 and 61853 mg/m3(1000, 2000, 3000, 4000, 5000 and 6000 ppm, respectively). No adverse effects at 30916 mg/m3 and lower. CNS effects at 41236 mg/m3 and higher.
  • Rats were exposed for 2 hours in a special study designed to establish a threshold for CNS effects observed in the 90-day subchronic toxicity test (IUCLID5 entry DI.K2.2 -Hr.InhVap.NEURO.HLR-395-95.CSR). The exposure concentrations were 10309, 15463, 25772, and 30926 mg/m3 (1000, 1500, 2500 and 3000 ppm, respectively). No adverse effects at 15463 mg/m3 and lower. CNS effects at 25772 mg/mand higher. 
  • Rats were exposed for 6 hr/day, 5 day/wk for 2 weeks in a special study designed to evaluate the potential for toxicity to appear in repeated exposures that did not occur in the acute exposure (IUCLID5 entry DI.K2.10-day.InhVap.NEURO.HLR-395-95.CSR). The exposure concentration was 10309 mg/m3. No adverse effects were observed.
  • Dogs were exposed for up to 10 minutes in a cardiac sensitisation test (IUCLID5 entry DI.K2.CardSen.D.DPT304/942241.CSR). Exposure concentrations were 10309, 51544 and 103088 mg/m3(1000, 5000 and 10000 ppm, respectively). No cardiac sensitisation occurred at any concentration tested, and no CNS effects were observed at 10309 mg/m3. CNS effects at 51544 mg/m3 and higher.

 

Based on the results shown above, conclusions can be drawn regarding the toxicity endpoint of highest concern, the exposure duration/toxicity relationship and the exposure threshold for the onset of toxicity. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in a subchronic inhalation scenario, indicating that adverse effects were not progressive, and that it was the exposure concentration, not the exposure duration that determined toxicological outcome. There were two studies with durations of 13 weeks or more. One was the OECD 413 (90-day subchronic inhalation test) and the other was the OECD 415 (One-generation reproductive toxicity study). In the OECD 413 study, CNS effects were observed at 20618 mg/m3, but not at the next lower exposure concentration of 5154 mg/m3. In the OECD 415 study, there were no CNS effects at 20618 mg/m3, in contrast to the OECD 413, but CNS effects were observed at the next higher exposure concentration of 36081 mg/m3. The results of the OECD 413 and OECD 415 tests further support the conclusion that the threshold for test substance-related CNS effects is approximately 20618 mg/m3. The special acute and repeated inhalation neurotoxicity studies provided the supplementary data needed to draw conclusions about expected CNS effects in the exposure concentration range between the 5154 and 20618 mg/m3. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern.The focused special studies conducted for the test substance make it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/m3 as the NAEL. This approach is preferred to the use of 5154 mg/m3 as a NAEL based on a study design in the 90-day subchronic toxicity test that did not include exposure concentrations between 5154 and 20618 mg/m3.The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3.   

 

The following figure (also attached in IU5) provides graphical representation of the data described above, and illustrates the basis for selecting 15463 mg/m3as a conservative NAEL for any acute or subchronic study selected as the study of highest concern for DNEL calculation. The Figure shows the CNS NAELs and LAELs for the various studies. The test numbers are defined as follows: 1= 2-hr special inhalation study (DI.K2.2-Hr.InhVap.NEURO.HLR-395-95.CSR), 2= 6 hr/day for 2 days in vivo micronucleus test (DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD), 3= special inhalation study 6 hr /day, 5 day/wk for 2 weeks (DI.K2.10 -day.InhVap.NEURO.R.HL-395 -95.CSR), 4= 6 hr/day, 7 day/wk for 10 days a developmental study (DI.K1.InhVap.DEV.R.HLR-255-94.KD), 5= 6 hr/day, 5 day/wk for 13 weeks (OECD 413) (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD), 6= 6 hr/day, 5 day/wk for approximately 15 weeks (OECD 415) (DI.K1.InhVap.1Gen.R.D-20699.KD), 7= 2-hr neurotoxicity study with extended exposure concentration range (DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). 

 

Step 1)

Description: Relevant dose-descriptor

Value: NOAEL: 15463 mg/m3

Remark:Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern.The focused special studies conducted for the test substance made it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/m3 as the NAEL. Please see text above for a detailed explanation. The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3. No adverse effects were observed in any study at an exposure concentration of 15463 mg/m3.

 

Step 2) 

Description: Modification of starting point for differences in respiratory volumes

Value: 0.67

Remark: A modification was applied to account for the increased respiratory volumes in active workers as compared to individuals at rest per REACH guidance R.8.4.2.

 

Description: Modification of starting point for worker exposure time

Value: 1

Remark: No modification of starting point is needed to correct for the worker exposure period as compared to the exposure periods used in the toxicity studies. The acute effects appeared very early in all of the inhalation exposures (within 1 hour). There was no increase in incidence or severity with increased exposure time, e.g. the toxicity was not progressive with time. Protecting the workers from the early occurring effects is the important aspect of establishing worker safe exposure levels. Adjustment for workplace exposure time is appropriate for substances which exhibit toxicity in a concentration x time manner or if there is an expectation that more serious adverse effects may appear with increasing exposure time. According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. The data presented in the DNEL derivation section above provide a basis for the justification that the adverse effects do not increase in severity or onset with increased exposure time. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in the repeated inhalation and subchronic inhalation scenarios, indicating that adverse effects are not progressive, and that it is the exposure concentration, not the exposure duration that determines toxicological outcome. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3, and a LAEL of approximately 20618 mg/m3.  These NAEL and LAEL values would be applicable to both acute and subchronic exposures. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Step 3)

Description: Assessment factor ─ Route of exposure

Value: 1

Remark: This is an inhalation -to-inhalation DNEL. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Allometric)

Value: 1

Remark: The exposure of interest is inhalation. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Other)

Value: 1

Remark: The “other interspecies” assessment factor is a composite of kinetic and dynamic factors. ECHA guidance document R.8.4.3.1 distinguishes between toxicity endpoints (effects) that are a function of direct chemical effects, and those endpoints that are associated with metabolite formation (e.g., where toxicity is a function of area-under-the-curve (AUC)). The test substance-specific data demonstrate that the adverse health effects of concern are a function of concentration, not AUC. In this respect, test substance toxicity is similar to direct contact toxicity substances where the adverse effects are a function of the physical chemical properties (e.g. pH, solubility, etc.). In such cases, the effects would be expected to behave in a qualitatively and quantitatively similar manner across laboratory animal species and humans. There was evidence of this in the tests involving rats and dogs, where there was consistency in the NAELs (no-adverse-effect-levels) and LAELs (low-adverse-effect-levels). This behaviour has led researches for several decades to use rats and dogs as valuable models for screening substances for anaesthetic properties in humans. While the arguments presented in the section support using something lower than the default value of 2.5, those arguments alone are not adequate to support reducing the assessment factor to 1. The basis for the use of an assessment factor of 1 relied on the arguments/data above, and the fact that inter- and intraspecies variability are not independent variables. In our dossier, we used the default assessment factor value of 5 for the intraspecies assessment factors. For the types of non-AUC effects observed with the test substance, we viewed the default intraspecies value of 5 for the worker as overly conservative. However, we decided to use the large intraspecies default assessment factor value, and reduce the “other interspecies” assessment value to arrive at an overall inter-/intraspecies assessment factor that would be appropriate for the type adverse effect observed during the robust testing of the test substance. If we had used the default interspecies assessment factor of 2.5, then we would have reduced the intraspecies assessment factor to 3 for the worker. The end result would have been essentially the same as the approach we used where we applied an “other interspecies” assessment factor of 1 and intraspecies assessment factor of 5.

 

Description: Assessment factor ─ Intraspecies

Value: 5

Remark: Default assessment factor for workers per REACH Guidance R.8.4.3.1. The selection of this value is highly conservative for the specific type of toxicity observed with the test substance. However, the basis for selection of such a high value is described in the interspecies assessment factor remarks above.

 

Description: Assessment factor – Exposure duration

Value: 1

Remark: According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. In order to ensure that our modification of the default assessment factor was consistent with ECHA guidance, we focused on 4 key characteristics: (1) the effect (transient CNS), (2) the NAELs in very short vs. subchronic exposures, (3) the likelihood of the test substance having a high bioresidence time and (4) AUC (area under the dose curve) or peak concentration relationship with CNS effects. The adverse effect associated with test substance inhalation is a transient CNS effect, and that is the effect of primary interest/concern for human health. As demonstrated by a robust dataset with exposures ranging from single 2-hr exposures to subchronic 6 hr/day exposures, the NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3 are applicable to all exposures, regardless of duration.  In other words, these NAEL and LAEL values were applicable to acute and subchronic exposures, and would be expected to apply to an extended (chronic) exposure. Further, the absence of adverse systemic toxicity or increased severity of the transient CNS effects with increasing exposure duration supports the position that the test substance does not have a high bioresidence time. Finally, the transient CNS effects have been demonstrated to occur as a function of concentration, and not as a function of AUC. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Description: Assessment factor – Dose response

Value: 1

Remark: The dose-descriptor is a no-adverse-effect-level, and the robust database supports the confidence in the dose- descriptor

 

Description: Assessment factor – Quality of database

Value: 1

Remark: A high quality, robust toxicity database exists for this substance.

 

Description: DNEL worker: long-term exposure systemic effects- inhalation

Value: 2072 mg/m3

 Remark: 15463 x 0.67 /(1 x 1 x 1 x 5 x 1 x 1 x 1) = 2072 mg/m3

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1 546 mg/m³
Most sensitive endpoint:
neurotoxicity
DNEL related information
Overall assessment factor (AF):
10
Modified dose descriptor starting point:
NOAEC
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
1 546 mg/m³
Most sensitive endpoint:
neurotoxicity
DNEL related information
Overall assessment factor (AF):
10
Modified dose descriptor starting point:
NOAEC

Local effects

Acute/short term exposure
DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure
DNEL related information

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
37 mg/kg bw/day
Most sensitive endpoint:
neurotoxicity
DNEL related information
Overall assessment factor (AF):
40
Acute/short term exposure
DNEL related information

General Population - Hazard for the eyes

Additional information - General Population

This is a volatile substance and general population long-term exposure is unlikely.  No local effects were observed in acute or repeated exposure studies; therefore, no DNEL for local effects was derived.

Justification for DN(ML) derivation/applied assessment factors – acute/short-term exposure – systemic effects

 

Acute test substance exposure potential for the general population is very low. However, if there were any acute exposures, they would occur via the inhalation route.

 

The test substance 4-hr LC50 is 114428 mg/m3 in rats. The test substance does not produce toxicity via the dermal or oral routes, is not a skin or eye irritant and is not a dermal sensitizer. During non-lethal, high concentration inhalation exposures, test substance toxicity was associated with transient central nervous systems (CNS) effects, which appeared early in the inhalation exposure. The effects included transient convulsions, similar to those observed during evaluation of test substance repeated inhalation toxicity. At concentrations below the threshold for CNS effects, no adverse effects were observed. 

 

Step 1)

Description: Relevant dose-descriptor

Value: NOAEL: 15463 mg/m3

Remark: The rat 4-hr LC50 was 114428 mg/m3, but at concentrations of 25772 mg/m3 and higher, central nervous system effects were seen in acute inhalation studies. No adverse effects were observed in any study at an exposure concentration of 15463 mg/m3.

 

Step 2)

 

Description: Modification of starting point for differences in respiratory volumes

Value: 1

Remark: No modification was applied since this DNEL is for the general population per REACH guidance R.8.4.2.

 

Description: Modification of starting point for general population exposure time

Value: 1

Remark: No modification of starting point is needed to correct for the general population exposure period as compared to the exposure periods used in the toxicity studies. The acute effects appeared very early in all of the inhalation exposures (within 1 hour). There was no increase in incidence or severity with increased exposure time, e.g. the toxicity was not progressive with time. Protecting the general population from the early occurring effects is the important aspect of establishing safe exposure levels.Adjustment for exposure time is appropriate for substances which exhibit toxicity in a concentration x time manner or if there is an expectation that more serious adverse effects may appear with increasing exposure time. According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. The data presented in the DNEL derivation section above provide a basis for the justification that the adverse effects do not increase in severity or onset with increased exposure time. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in the repeated inhalation and subchronic inhalation scenarios, indicating that adverse effects are not progressive, and that it is the exposure concentration, not the exposure duration that determines toxicological outcome. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3, and a LAEL of approximately 20618 mg/m3.  These NAEL and LAEL values would be applicable to both acute and subchronic exposures. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

 

Step 3)

Description: Assessment factor ─ Route of exposure

Value: 1

Remark: This is an inhalation -to-inhalation DNEL. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Allometric)

Value: 1

Remark: The exposure of interest is inhalation. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Other)

Value: 1

Remark: The “other interspecies” assessment factor is a composite of kinetic and dynamic factors. ECHA guidance document R.8.4.3.1 distinguishes between toxicity endpoints (effects) that are a function of direct chemical effects, and those endpoints that are associated with metabolite formation (e.g., where toxicity is a function of area-under-the-curve (AUC)). The test substance-specific data demonstrate that the adverse health effects of concern are a function of concentration, not AUC. In this respect, test substance toxicity is similar to direct contact toxicity substances where the adverse effects are a function of the physical chemical properties (e.g. pH, solubility, etc.). In such cases, the effects would be expected to behave in a qualitatively and quantitatively similar manner across laboratory animal species and humans. There was evidence of this in the test substance tests involving rats and dogs, where there was consistency in the NAELs (no-adverse-effect-levels) and LAELs (low-adverse-effect-levels). This behaviour has led researches for several decades to use rats and dogs as valuable models for screening substances for anaesthetic properties in humans. While the arguments presented in the section support using something lower than the default value of 2.5, those arguments alone are not adequate to support reducing the assessment factor to 1. The basis for the use of an assessment factor of 1 relied on the arguments/data above, and the fact that inter- and intraspecies variability are not independent variables. In our dossier, we used the default assessment factor value of 10 for the intraspecies assessment factors. For the types of non-AUC effects observed with the tests substance, we viewed the default intraspecies value of 10 for the general population as overly conservative. However, we decided to use the large intraspecies default assessment factor value, and reduce the “other interspecies” assessment value to arrive at an overall inter-/intraspecies assessment factor that would be appropriate for the type adverse effect observed during the robust testing of the test substance. If we had used the default interspecies assessment factor of 2.5, then we would have reduced the intraspecies assessment factor to 5 for the general population. The end result would have been essentially the same as the approach we used where we applied an “other interspecies” assessment factor of 1 and intraspecies assessment factor of 10.

 

Description: Assessment factor ─ Intraspecies

Value: 10

Remark: Default assessment factor for the general population per REACH Guidance R.8.4.3.1. The selection of this value is highly conservative for the specific type of toxicity observed with the test substance. However, the basis for selection of such a high value is described in the interspecies assessment factor remarks above.

 

Description: Assessment factor – Exposure duration

Value: 1

Remark: According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. In order to ensure that our modification of the default assessment factor was consistent with ECHA guidance, we focused on 4 key characteristics: (1) the effect (transient CNS), (2) the NAELs in very short vs. subchronic exposures, (3) the likelihood of the test substance having a high bioresidence time and (4) AUC (area under the dose curve) or peak concentration relationship with CNS effects. The adverse effect associated with test substance inhalation is a transient CNS effect, and that is the effect of primary interest/concern for human health. As demonstrated by a robust dataset with exposures ranging from single 2-hr exposures to subchronic 6 hr/day exposures, the NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3 are applicable to all exposures, regardless of duration.  In other words, these NAEL and LAEL values were applicable to acute and subchronic exposures, and would be expected to apply to an extended (chronic) exposure. Further, the absence of adverse systemic toxicity or increased severity of the transient CNS effects with increasing exposure duration supports the position that the test substance does not have a high bioresidence time. Finally, the transient CNS effects have been demonstrated to occur as a function of concentration, and not as a function of AUC. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Description: Assessment factor – Dose response

Value: 1

Remark: The dose-descriptor is a no-adverse-effect-level, and the robust database supports the confidence in the dose- descriptor

 

Description: Assessment factor – Quality of database

Value: 1

Remark: A high quality, robust toxicity database exists for this substance.

 

Description: DNEL general population: acute/short-term exposure systemic effects- inhalation

Value: 1546 mg/m3

Remark: 15463 /(1 x 1 x 1 x 10 x 1 x 1 x 1) = 1546 mg/m3

 

 

Justification for DN(ML) derivation/applied assessment factors – long-term exposure – systemic effects (Inhalation DN(M)EL)

 

Long-term test substance exposure potential for the general population is very low. However, if there were any exposures, they could occur via the inhalation route

 

The test substance 4-hr LC50 is 114428 mg/m3 in rats. The test substance does not produce toxicity via the dermal or oral routes, is not a skin or eye irritant and is not a dermal sensitizer. The test substance does not present genetic, pre-natal developmental or reproductive toxicity concerns, and no systemic organ damage was observed in subchronic inhalation toxicity studies. During non-lethal, high concentration inhalation exposures, test substance toxicity was associated with transient central nervous systems (CNS) effects, which appeared early in the inhalation exposure. The effects included transient convulsions, similar to those observed during evaluation of test substance repeated inhalation toxicity. At concentrations below the threshold for CNS effects, no adverse effects were observed. 

 

The qualitatively and quantitatively consistent presentation of a single toxicological effect (transient CNS effects) across all studies, regardless of exposure duration, provided a unique opportunity to clearly identify the health effect of highest concern, and an exposure threshold for the occurrence of the effects. This was accomplished by the conduct of robust, special studies using test substance exposure concentrations spanning those used in repeated exposure and subchronic studies. Details of the testing approach and relevant outcomes are provided in the following segments.

  • The initial testing plan was fairly standard, and included a phased approach where testing starting with acute toxicity, eye/skin irritation, sensitisation and in vitro genetic toxicity tests.  Following the initial phase, pre-natal developmental, subchronic, in vivo genetic and reproductive toxicity tests were conducted. Evaluation of the available data, led to the conduct of follow-on special studies specifically designed to enhance hazard data for use in human safety and risk assessment activities.
  • Rats were exposed for 4 hours in the 4-hr LC50 test (IUCLID5 entry DI.K1.4Hr.InhVap.R.HLO-626-96.KD). Design concentrations were 51544, 103088 and 206176 mg/m3 (5000, 10000 and 20000 ppm, respectively). CNS effects occurred at all concentrations. 
  • Rats were exposed 6 hr/day for 2 days in the in vivo micronucleus test (IUCLID5 entry DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD). Concentrations were 20618, 36081 and 72162 mg/m3 (2000, 3500, 7000 ppm, respectively). No adverse effects at 20681 mg/m3. CNS effects at 36081 mg/m3 and higher. 
  • Rats were exposed 6 hr/day, 7 day/wk for 10 days in the developmental toxicity test (IUCLID5 entry DI.K1.InhVap.DEV.R.HLR-255-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Rats were exposed 6 hr/day, 5 day/wk for 13 weeks in the OECD 413 90-day subchronic toxicity test (IUCLID5 entry DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Male rats were exposed 6 hr/day, 5 day/wk for 10 weeks, followed by 6 hr/day, 7 day/wk for 5 weeks, and females exposed 6 hr/day, 5 day/wk for approximately 10 weeks, followed by 6 hr/day, 7 day/wk for approximately 7 weeks in the OECD 415 reproductive toxicity test (IUCLID5 entry DI.K1.InhVap.1Gen.R.D-20699.KD). This study represented the longest exposure duration of any of the test substance studies. The exposure concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 20618 mg/m3 and lower. CNS effects at 36081 mg/m3.
  • Rats were exposed for 2 hours in a neurotoxicity test (IUCLID5 entry DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). The exposure concentrations were 10309, 20618, 30926, 41236, 51544 and 61853 mg/m3 (1000, 2000, 3000, 4000, 5000 and 6000 ppm, respectively). No adverse effects at 30916 mg/m3and lower. CNS effects at 41236 mg/m3 and higher.
  • Rats were exposed for 2 hours in a special study designed to establish a threshold for CNS effects observed in the 90-day subchronic toxicity test (IUCLID5 entry DI.K2.2 -Hr.InhVap.NEURO.HLR-395-95.CSR). The exposure concentrations were 10309, 15463, 25772, and 30926 mg/m3 (1000, 1500, 2500 and 3000 ppm, respectively). No adverse effects at 15463 mg/m3 and lower. CNS effects at 25772 mg/mand higher. 
  • Rats were exposed for 6 hr/day, 5 day/wk for 2 weeks in a special study designed to evaluate the potential for toxicity to appear in repeated exposures that did not occur in the acute exposure (IUCLID5 entry DI.K2.10-day.InhVap.NEURO.HLR-395-95.CSR). The exposure concentration was 10309 mg/m3. No adverse effects were observed.
  • Dogs were exposed for up to 10 minutes in a cardiac sensitisation test (IUCLID5 entry DI.K2.CardSen.D.DPT304/942241.CSR). Exposure concentrations were 10309, 51544 and 103088 mg/m(1000, 5000 and 10000 ppm, respectively). No cardiac sensitisation occurred at any concentration tested, and no CNS effects were observed at 10309 mg/m3. CNS effects at 51544 mg/m3and higher.

 

Based on the results shown above, conclusions can be drawn regarding the toxicity endpoint of highest concern, the exposure duration/toxicity relationship and the exposure threshold for the onset of toxicity. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in a subchronic inhalation scenario, indicating that adverse effects were not progressive, and that it was the exposure concentration, not the exposure duration that determined toxicological outcome. There were two studies with durations of 13 weeks or more. One was the OECD 413 (90-day subchronic inhalation test) and the other was the OECD 415 (One-generation reproductive toxicity study). In the OECD 413 study, CNS effects were observed at 20618 mg/m3, but not at the next lower exposure concentration of 5154 mg/m3. In the OECD 415 study, there were no CNS effects at 20618 mg/m3, in contrast to the OECD 413, but CNS effects were observed at the next higher exposure concentration of 36081 mg/m3. The results of the OECD 413 and OECD 415 tests further support the conclusion that the threshold for test substance-related CNS effects is approximately 20618 mg/m3. The special acute and repeated inhalation neurotoxicity studies provided the supplementary data needed to draw conclusions about expected CNS effects in the exposure concentration range between the 5154 and 20618 mg/m3. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern.The focused special studies conducted for the test substance make it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/m3 as the NAEL. This approach is preferred to the use of 5154 mg/m3 as a NAEL based on a study design in the 90-day subchronic toxicity test that did not include exposure concentrations between 5154 and 20618 mg/m3. The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3.   

 

The following figure (also attached in IU5) provides graphical representation of the data described above, and illustrates the basis for selecting 15463 mg/m3 as a conservative NAEL for any acute or subchronic study selected as the study of highest concern for DNEL calculation. The Figure shows the CNS NAELs and LAELs for the various studies. The test numbers are defined as follows: 1= 2-hr special inhalation study (DI.K2.2 -Hr.InhVap.NEURO.HLR-395-95.CSR), 2= 6 hr/day for 2 days in vivo micronucleus test (DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD), 3= special inhalation study 6 hr /day, 5 day/wk for 2 weeks (DI.K2.10 -day.InhVap.NEURO.R.HL-395 -95.CSR), 4= 6 hr/day, 7 day/wk for 10 days a developmental study (DI.K1.InhVap.DEV.R.HLR-255-94.KD), 5= 6 hr/day, 5 day/wk for 13 weeks (OECD 413) (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD), 6= 6 hr/day, 5 day/wk for approximately 15 weeks (OECD 415) (DI.K1.InhVap.1Gen.R.D-20699.KD), 7= 2-hr neurotoxicity study with extended exposure concentration range (DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). 

Step 1)

Description: Relevant dose-descriptor

Value: NOAEL: 15463 mg/m3

Remark: Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern.The focused special studies conducted for the test substance made it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/3 as the NAEL. Please see text above for a detailed explanation. The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3.No adverse effects were observed in any study at an exposure concentration of 15463 mg/m3.

 

Step 2)

Description: Modification of starting point for differences in respiratory volumes

Value: 1

Remark: No modification was applied to account for the general population per REACH guidance R.8.4.2.

 

Description: Modification of starting point for general population exposure time

Value: 1

Remark: No modification of starting point is needed to correct for the general population exposure period as compared to the exposure periods used in the toxicity studies. The acute effects appeared very early in all of the inhalation exposures (within 1 hour). There was no increase in incidence or severity with increased exposure time, e.g. the toxicity was not progressive with time. Protecting the general population from the early occurring effects is the important aspect of establishing safe exposure levels. Adjustment for exposure time is appropriate for substances which exhibit toxicity in a concentration x time manner, or if there is an expectation that more serious adverse effects may appear with increasing exposure time. According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. The data presented in the DNEL derivation section above provide a basis for the justification that the adverse effects do not increase in severity or onset with increased exposure time. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in the repeated inhalation and subchronic inhalation scenarios, indicating that adverse effects are not progressive, and that it is the exposure concentration, not the exposure duration that determines toxicological outcome. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3, and a LAEL of approximately 20618 mg/m3.  These NAEL and LAEL values would be applicable to both acute and subchronic exposures. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

 

Step 3)

Description: Assessment factor ─ Route of exposure

Value: 1

Remark: This is an inhalation -to-inhalation DNEL. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Allometric)

Value: 1

Remark: The exposure of interest is inhalation. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Other)

Value: 1

Remark: The “other interspecies” assessment factor is a composite of kinetic and dynamic factors. ECHA guidance document R.8.4.3.1 distinguishes between toxicity endpoints (effects) that are a function of direct chemical effects, and those endpoints that are associated with metabolite formation (e.g., where toxicity is a function of area-under-the-curve (AUC)). The test substance-specific data demonstrate that the adverse health effects of concern are a function of concentration, not AUC. In this respect, test substance toxicity is similar to direct contact toxicity substances where the adverse effects are a function of the physical chemical properties (e.g. pH, solubility, etc.). In such cases, the effects would be expected to behave in a qualitatively and quantitatively similar manner across laboratory animal species and humans. There was evidence of this in the tests involving rats and dogs, where there was consistency in the NAELs (no-adverse-effect-levels) and LAELs (low-adverse-effect-levels). This behaviour has led researches for several decades to use rats and dogs as valuable models for screening substances for anaesthetic properties in humans. While the arguments presented in the section support using something lower than the default value of 2.5, those arguments alone are not adequate to support reducing the assessment factor to 1. The basis for the use of an assessment factor of 1 relied on the arguments/data above, and the fact that inter- and intraspecies variability are not independent variables. In our dossier, we used the default assessment factor value of 10 for the intraspecies assessment factors. For the types of non-AUC effects observed with the test substance, we viewed the default intraspecies value of 10 for the general population as overly conservative. However, we decided to use the large intraspecies default assessment factor values, and reduce the “other interspecies” assessment value to arrive at an overall inter-/intraspecies assessment factor that would be appropriate for the type adverse effect observed during the robust testing of the test substance. If we had used the default interspecies assessment factor of 2.5, then we would have reduced the intraspecies assessment factor to 5 for the general population. The end result would have been essentially the same as the approach we used where we applied an “other interspecies” assessment factor of 1 and intraspecies assessment factor of 10.

 

Description: Assessment factor ─ Intraspecies

Value: 10

Remark: Default assessment factor for workers per REACH Guidance R.8.4.3.1. The selection of this value is highly conservative for the specific type of toxicity observed with the test substance. However, the basis for selection of such a high value is described in the interspecies assessment factor remarks above.

 

Description: Assessment factor – Exposure duration

Value: 1

Remark: According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. In order to ensure that our modification of the default assessment factor was consistent with ECHA guidance, we focused on 4 key characteristics: (1) the effect (transient CNS), (2) the NAELs in very short vs. subchronic exposures, (3) the likelihood of the test substance having a high bioresidence time and (4) AUC (area under the dose curve) or peak concentration relationship with CNS effects. The adverse effect associated with test substance inhalation is a transient CNS effect, and that is the effect of primary interest/concern for human health. As demonstrated by a robust dataset with exposures ranging from single 2-hr exposures to subchronic 6 hr/day exposures, the NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3 are applicable to all exposures, regardless of duration.  In other words, these NAEL and LAEL values were applicable to acute and subchronic exposures, and would be expected to apply to an extended (chronic) exposure. Further, the absence of adverse systemic toxicity or increased severity of the transient CNS effects with increasing exposure duration supports the position that the test substance does not have a high bioresidence time. Finally, the transient CNS effects have been demonstrated to occur as a function of concentration, and not as a function of AUC. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Description: Assessment factor – Dose response

Value: 1

Remark: The dose-descriptor is a no-adverse-effect-level, and the robust database supports the confidence in the dose- descriptor

 

Description: Assessment factor – Quality of database

Value: 1

Remark: A high quality, robust toxicity database exists for this substance.

 

Description: DNEL general population: long-term exposure systemic effects- inhalation

Value: 1546 mg/m3

Remark: 15463 /(1 x 1 x 1 x 10 x 1 x 1 x 1) = 1546 mg/m3

 

Justification for DN(ML) derivation/applied assessment factors – long-term exposure – systemic effects (Oral DN(M)EL)

 

Potential general population exposure to the test substance is unlikely, and any exposure that did occur would likely occur via inhalation.  However, an oral DNEL was derived for use in any risk assessment involving the highly unlikely oral route of exposure.

 

The test substance 4-hr LC50 is 114428 mg/m3 in rats. The test substance does not produce toxicity via the dermal or oral routes, is not a skin or eye irritant and is not a dermal sensitizer. The test substance does not present genetic, pre-natal developmental or reproductive toxicity concerns, and no systemic/organ damage was observed in subchronic inhalation toxicity studies. During non-lethal, high concentration inhalation exposures, test substance toxicity was associated with transient central nervous systems (CNS) effects, which appeared early in the inhalation exposure. The effects included transient convulsions, similar to those observed during evaluation of various substances with potential anaesthetic. At concentrations below the threshold for CNS effects, no adverse effects were observed. 

 

The qualitatively and quantitatively consistent presentation of a single toxicological effect (transient CNS effects) across all studies, regardless of exposure duration, provided a unique opportunity to clearly identify the health effect of highest concern, and an exposure threshold for the occurrence of the effects. This was accomplished by the conduct of robust, special studies using test substance exposure concentrations spanning those used in repeated exposure and subchronic studies. Details of the testing approach and relevant outcomes are provided in the following segments.

  • The initial testing plan was fairly standard, and included a phased approach where testing starting with acute toxicity, eye/skin irritation, sensitisation and in vitro genetic toxicity tests.  Following the initial phase, pre-natal developmental, subchronic, in vivo genetic and reproductive toxicity tests were conducted. Evaluation of the available data, led to the conduct of follow-on special studies specifically designed to enhance hazard data for use in human safety and risk assessment activities.
  • Rats were exposed for 4 hours in the 4-hr LC50 test (IUCLID5 entry DI.K1.4Hr.InhVap.R.HLO-626-96.KD). Design concentrations were 51544, 103088 and 206176 mg/m3 (5000, 10000 and 20000 ppm, respectively). CNS effects occurred at all concentrations. 
  • Rats were exposed 6 hr/day for 2 days in the in vivo micronucleus test (IUCLID5 entry DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD). Concentrations were 20618, 36081 and 72162 mg/m3 (2000, 3500, 7000 ppm, respectively). No adverse effects at 20681 mg/m3. CNS effects at 36081 mg/m3 and higher. 
  • Rats were exposed 6 hr/day, 7 day/wk for 10 days in the developmental toxicity test (IUCLID5 entry DI.K1.InhVap.DEV.R.HLR-255-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Rats were exposed 6 hr/day, 5 day/wk for 13 weeks in the OECD 413 90-day subchronic toxicity test (IUCLID5 entry DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD). Concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 5154 mg/m3. CNS effects at 20618 mg/m3 and higher.
  • Male rats were exposed 6 hr/day, 5 day/wk for 10 weeks, followed by 6 hr/day, 7 day/wk for 5 weeks, and females exposed 6 hr/day, 5 day/wk for approximately 10 weeks, followed by 6 hr/day, 7 day/wk for approximately 7 weeks in the OECD 415 reproductive toxicity test (IUCLID5 entry DI.K1.InhVap.1Gen.R.D-20699.KD). This study represented the longest exposure duration of any of the test substance studies. The exposure concentrations were 5154, 20618 and 36081 mg/m3 (500, 2000 and 3500 ppm, respectively). No adverse effects at 20618 mg/m3 and lower. CNS effects at 36081 mg/m3.
  • Rats were exposed for 2 hours in a neurotoxicity test (IUCLID5 entry DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). The exposure concentrations were 10309, 20618, 30926, 41236, 51544 and 61853 mg/m3 (1000, 2000, 3000, 4000, 5000 and 6000 ppm, respectively). No adverse effects at 30916 mg/m3 and lower. CNS effects at 41236 mg/m3 and higher.
  • Rats were exposed for 2 hours in a special study designed to establish a threshold for CNS effects observed in the 90-day subchronic toxicity test (IUCLID5 entry DI.K2.2-Hr.InhVap.NEURO.HLR-395-95.CSR). The exposure concentrations were 10309, 15463, 25772, and 30926 mg/m3 (1000, 1500, 2500 and 3000 ppm, respectively). No adverse effects at 15463 mg/m3 and lower. CNS effects at 25772 mg/mand higher. 
  • Rats were exposed for 6 hr/day, 5 day/wk for 2 weeks in a special study designed to evaluate the potential for toxicity to appear in repeated exposures that did not occur in the acute exposure (IUCLID5 entry DI.K2.10-day.InhVap.NEURO.HLR-395-95.CSR). The exposure concentration was 10309 mg/m3. No adverse effects were observed.
  • Dogs were exposed for up to 10 minutes in a cardiac sensitisation test (IUCLID5 entry DI.K2.CardSen.D.DPT304/942241.CSR). Exposure concentrations were 10309, 51544 and 103088 mg/m3 (1000, 5000 and 10000 ppm, respectively). No cardiac sensitisation occurred at any concentration tested, and no CNS effects were observed at 10309 mg/m3. CNS effects at 51544 mg/m3 and higher.

 

Based on the results shown above, conclusions can be drawn regarding the toxicity endpoint of highest concern, the exposure duration/toxicity relationship and the exposure threshold for the onset of toxicity. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in a subchronic inhalation scenario, indicating that adverse effects were not progressive, and that it was the exposure concentration, not the exposure duration that determined toxicological outcome. There were two studies with durations of 13 weeks or more. One was the OECD 413 (90-day subchronic inhalation test) and the other was the OECD 415 (One-generation reproductive toxicity study). In the OECD 413 study, CNS effects were observed at 20618 mg/m3, but not at the next lower exposure concentration of 5154 mg/m3. In the OECD 415 study, there were no CNS effects at 20618 mg/m3, in contrast to the OECD 413, but CNS effects were observed at the next higher exposure concentration of 36081 mg/m3. The results of the OECD 413 and OECD 415 tests further support the conclusion that the threshold for test substance related CNS effects is approximately 20618 mg/m3. The special acute and repeated inhalation neurotoxicity studies provided the supplementary data needed to draw conclusions about expected CNS effects in the exposure concentration range between the 5154 and 20618 mg/m3. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern. The focused special studies conducted for the test substance make it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/3 as the NAEL. This approach is preferred to the use of 5154 mg/m3 as a NAEL based on a study design in the 90-day subchronic toxicity test that did not include exposure concentrations between 5154 and 20618 mg/m3. The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3.   

 

The following figure (also attached in IU5) provides graphical representation of the data described above, and illustrates the basis for selecting 15463 mg/m3 as a conservative NAEL for any acute or subchronic study selected as the study of highest concern for DNEL calculation. The Figure shows the CNS NAELs and LAELs for the various studies. The test numbers are defined as follows: 1= 2-hr special inhalation study (DI.K2.2 -Hr.InhVap.NEURO.HLR-395-95.CSR), 2= 6 hr/day for 2 days in vivo micronucleus test (DI.K1.2Day.InhVap.MicroNuc.R.HLR-53-94.KD), 3= special inhalation study 6 hr /day, 5 day/wk for 2 weeks (DI.K2.10-day.InhVap.NEURO.R.HL-395 -95.CSR), 4= 6 hr/day, 7 day/wk for 10 days a developmental study (DI.K1.InhVap.DEV.R.HLR-255-94.KD), 5= 6 hr/day, 5 day/wk for 13 weeks (OECD 413) (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD), 6= 6 hr/day, 5 day/wk for approximately 15 weeks (OECD 415) (DI.K1.InhVap.1Gen.R.D-20699.KD), 7= 2-hr neurotoxicity study with extended exposure concentration range (DI.K2.2-Hr.NEURO.R.HL-781-96.CSR). 

Step 1)

Description: Relevant dose-descriptor

Value: NOAEL: 1484 mg/kg bw/day

Remark: Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3. These NAEL and LAEL values would be applicable to both acute and subchronic exposures, and therefore the NAEL used as the DNEL starting point would be the same if an acute study or a subchronic study were selected as the study of highest concern. The focused special studies conducted for the test substance made it possible to evaluate the exposure-response relationship between 5154 and 20618 mg/m3 in the 90-day subchronic toxicity test, and select the scientifically credible value of 15463 mg/m3 as the NAEL. Please see text above for a detailed explanation.The robust dataset available for the test substance supports the position that if the 90-day inhalation toxicity test (DI.K1.90-day.InhVap.Neuro.R.HLR-24-94.KD) was selected as the study of highest concern, the NAEL should be set at 15463 mg/m3No adverse effects were observed in any study at an exposure concentration of 15463 mg/m3. This value was converting to an oral value (mg/kgbw/day) by adjusting the inhalation value of 15463 mg/m3 for ventilation rate and study duration (15463 x 2 x 60 x 0.8/1000 = 1484 mg/kg bw/day).

 

Step 2)

Description: Modification of starting point for general population exposure time

Value: 1

Remark: No modification of starting point is needed to correct for the general population exposure period as compared to the exposure periods used in the toxicity studies. No toxicity was observed in the oral toxicity study conducted at 5000 mg/kg bw/day in rats. In inhalation studies, the effects appeared very early in all of the inhalation exposures (within 1 hour). There was no increase in incidence or severity with increased exposure time, e.g. the toxicity was not progressive with time. Protecting the general population from the early occurring effects is the important aspect of establishing safe exposure levels. Adjustment for exposure time is appropriate for substances which exhibit toxicity in a concentration x time manner or if there is an expectation that more serious adverse effects may appear with increasing exposure time. According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. The data presented in the DNEL derivation section above provide a basis for the justification that the adverse effects do not increase in severity or onset with increased exposure time. The only adverse health effect associated with test substance exposure was a transient CNS effect. The adverse effects were the same in a 2-hr inhalation scenario as in the repeated inhalation and subchronic inhalation scenarios, indicating that adverse effects are not progressive, and that it is the exposure concentration, not the exposure duration that determines toxicological outcome. Based on an assessment of all relevant inhalation data, the health effect of highest concern is a transient CNS effect with a NAEL of 15463 mg/m3, and a LAEL of approximately 20618 mg/m3.  These NAEL and LAEL values would be applicable to both acute and subchronic exposures. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

 

Step 3)

Description: Assessment factor ─ Route of exposure

Value: 1

Remark: This is an inhalation -to-oral DNEL. A default factor of 1 is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Allometric)

Value: 4

Remark: A default factor of 4 to account for interspecies differences in metabolic activity is appropriate per REACH Guidance R.8.4.3.1

 

Description: Assessment factor ─ Interspecies (Other)

Value: 1

Remark: The “other interspecies” assessment factor is a composite of kinetic and dynamic factors. ECHA guidance document R.8.4.3.1 distinguishes between toxicity endpoints (effects) that are a function of direct chemical effects, and those endpoints that are associated with metabolite formation (e.g., where toxicity is a function of area-under-the-curve (AUC)). The test substance-specific data demonstrate that the adverse health effects of concern are a function of concentration, not AUC. In this respect, test substance toxicity is similar to direct contact toxicity substances where the adverse effects are a function of the physical chemical properties (e.g. pH, solubility, etc.). In such cases, the effects would be expected to behave in a qualitatively and quantitatively similar manner across laboratory animal species and humans. There was evidence of this in the tests involving rats and dogs, where there was consistency in the NAELs (no-adverse-effect-levels) and LAELs (low-adverse-effect-levels). This behaviour has led researches for several decades to use rats and dogs as valuable models for screening substances for anaesthetic properties in humans. While the arguments presented in the section support using something lower than the default value of 2.5, those arguments alone are not adequate to support reducing the assessment factor to 1. The basis for the use of an assessment factor of 1 relied on the arguments/data above, and the fact that inter- and intraspecies variability are not independent variables. In our dossier, we used the default assessment factor value of 10 for the intraspecies assessment factors. For the types of non-AUC effects observed with the test substance, we viewed the default intraspecies value of 10 for the general population as overly conservative. However, we decided to use the large intraspecies default assessment factor values, and reduce the “other interspecies” assessment value to arrive at an overall inter-/intraspecies assessment factor that would be appropriate for the type adverse effect observed during the robust testing of the test substance. If we had used the default interspecies assessment factor of 2.5, then we would have reduced the intraspecies assessment factor to 5 for the general population. The end result would have been essentially the same as the approach we used where we applied an “other interspecies” assessment factor of 1 and intraspecies assessment factor of 10.

 

Description: Assessment factor ─ Intraspecies

Value: 10

Remark: Default assessment factor for workers per REACH Guidance R.8.4.3.1. The selection of this value is highly conservative for the specific type of toxicity observed with the test substance. However, the basis for selection of such a high value is described in the interspecies assessment factor remarks above.

 

Description: Assessment factor – Exposure duration

Value: 1

Remark: According to ECHA guidance document R.8.4.3.1, substance-specific information should be used to modify the default value for exposure duration. Specifically, R.8.4.3.1 mentions that a reduction in the assessment factor is justified where there is evidence that increased exposure time does not increase the incidence/severity of adverse effects. In order to ensure that our modification of the default assessment factor was consistent with ECHA guidance, we focused on 4 key characteristics: (1) the effect (transient CNS), (2) the NAELs in very short vs. subchronic exposures, (3) the likelihood of the test substance having a high bioresidence time and (4) AUC (area under the dose curve) or peak concentration relationship with CNS effects. The adverse effect associated with test substance inhalation is a transient CNS effect, and that is the effect of primary interest/concern for human health. As demonstrated by a robust dataset with exposures ranging from single 2-hr exposures to subchronic 6 hr/day exposures, the NAEL of 15463 mg/m3 and a LAEL of approximately 20618 mg/m3 are applicable to all exposures, regardless of duration.  In other words, these NAEL and LAEL values were applicable to acute and subchronic exposures, and would be expected to apply to an extended (chronic) exposure. Further, the absence of adverse systemic toxicity or increased severity of the transient CNS effects with increasing exposure duration supports the position that the test substance does not have a high bioresidence time. Finally, the transient CNS effects have been demonstrated to occur as a function of concentration, and not as a function of AUC. The test substance-specific data justify modification of the default assessment factor, and support our assessment value of 1.

 

Description: Assessment factor – Dose response

Value: 1

Remark: The dose-descriptor is a no-adverse-effect-level, and the robust database supports the confidence in the dose- descriptor

 

Description: Assessment factor – Quality of database

Value: 1

Remark: A high quality, robust toxicity database exists for this substance.

 

Description: DNEL general population: long-term exposure systemic effects- oral

Value: 37 mg/kg bw/day

Remark: 1484 /(1 x 4 x 1 x 10 x 1 x 1 x 1) = 37 mg/kg bw/day