2-ethyl-4-methylimidazole

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

2.8 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

25

Modified dose descriptor starting point:

NOAEC

Value:

70 mg/m³

Explanation for the modification of the dose descriptor starting point:

NOAEC = NOAEL (90d, oral, rat) *abs oral/abs inhal /0.38 m3/kg bw *6.7 m3/10 m3 = NOAEL /(2*0,38) *0.67 (R.8.4.2)

AF for dose response relationship:

1

Justification:

GLP study according to OECD TG 408 with 3 doses

AF for differences in duration of exposure:

2

Justification:

Subchronic to chronic extrapolation

AF for interspecies differences (allometric scaling):

1

Justification:

No allometric scaling has to be applied in case of oral to inhalation route to route extrapolation.

AF for other interspecies differences:

2.5

Justification:

default

AF for intraspecies differences:

5

Justification:

default for workers

AF for the quality of the whole database:

1

Justification:

sufficient reliable data available

AF for remaining uncertainties:

1

Justification:

default

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1.6 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

100

Modified dose descriptor starting point:

NOAEL

Value:

160 mg/kg bw/day

Explanation for the modification of the dose descriptor starting point:

NOAEL = NOAEL (90d, oral, rat) * abs.oral/abs.dermal = 80 mg/kg bw/d * 0.5

AF for dose response relationship:

1

Justification:

GLP study according to OECD TG 408 with 3 doses

AF for differences in duration of exposure:

2

Justification:

Subchronic to chronic extrapolation

AF for interspecies differences (allometric scaling):

4

Justification:

default for rat to man

AF for other interspecies differences:

2.5

Justification:

default

AF for intraspecies differences:

5

Justification:

default for workers

AF for the quality of the whole database:

1

Justification:

sufficient reliable data available

AF for remaining uncertainties:

1

Justification:

default

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

289 µg/cm²

Most sensitive endpoint:

sensitisation (skin)

DNEL related information

DNEL derivation method:

other: see discussion

Overall assessment factor (AF):

10

Acute/short term exposure

Hazard assessment conclusion:

low hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - workers

Toxicokinetic

No data on absorption are available. According to Chapter R.8 of REACH Guidance on information requirements and chemical safety assessment, it is proposed in the absence of route-specific information on the starting route, to include a default factor of 2 in the case of oral-to-inhalation extrapolation. This approach will be taken forward to DNEL derivation. For the dermal absorption could be considered to be maximal 50 % of the oral absorption.

 

Acute toxicity

2-Ethyl-4-methylimidazole has to be classified for acute oral toxicity. However, a short-term DNEL is deemed unnecessary because the long-term DNELs are considered to ensure sufficient protection to prevent peak exposure.

 

Repeated dose toxicity

The administration of 2-Ethyl-4-methylimidazole by gavage to male and female Wistar rats for 3 months caused signs of systemic toxicity only at the high dose level of 230 mg/kg bw/d: decreased body weight and body weight gain; increased total white blood cell (WBC) and absolute neutrophil counts in males, increased urea, cholesterol and inorganic phosphate levels in both sexes, decreased chloride levels in both sexes, increased triglyceride levels in females and decreased albumin levels in females; decreased terminal body weight in both sexes, increased mean absolute and relative liver weights in females and minimal centrilobular hepatocellular hypertrophy in 9/10 female animals. Therefore, under the conditions of the present study the no observed adverse effect level (NOAEL) was 80 mg/kg bw/d for male and female Wistar rats.

This is supported by a GLP compliant combined 28 -days repeated dose toxicity study with reproduction/developmental toxicity screening test. 2 -Ethyl-4-methylimidazole was given to rats by oral gavage at dose levels of 0, 15, 50 or 150 mg/kg bw/d. Lower levels of total protein and albumin at 150 mg/kg bw/day were noted for females, and higher liver weights (absolute and relative to body weight) were recorded at 15, 50 and 150 mg/kg bw/day for males. These changes were minor or showed no dose-related response. No other treatment-related effects indicative of systemic availability were observed. Furthermore, no reproduction and developmental toxicity was observed up to the highest dose level tested (150 mg/kg bw/day). Based on these results, a parental, reproduction and developmental NOAEL of at least 150 mg/kg bw/day was derived.

 

Irritation / Sensitisation / Mutagenicity

2-ethyl-4-methylimidazole is considered to be irritating to the skin and eye. Since only a qualitative assessment was made on the irritating potential of 2-ethyl-4-methylimidazole to the skin, no local acute DNEL for dermal exposure could be derived.

2-ethyl-4-methylimidazole is considered to be sensitizing to the skin. In a LLNA, an EC3 of 14.2% (w/w) was derived.

2-ethyl-4-methylimidazole was not mutagenic in the reverse mutation assays performed, in anin vitroHPRT test, and in anin vitromicronucleus test. Therefore, 2-ethyl-4-methylimidazole is considered to be non-mutagenic.

 

DNEL derivation

For short-term toxicity, no DNEL needs to be derived for all routes of exposure, because the long-term DNELs are considered to ensure sufficient protection to prevent peak exposure. There are no consumer uses for 2-ethyl-4-methylimidazole, nevertheless the systemic long-term DNELs were derived.

 

Oral:For long-term toxicity, regarding systemic effects, a NOAEL of 80 mg/kg bw/day was observed in a 90 day repeated dose toxicity study. This NOAEL is used in the derivation of the DNELs. An absorption of 50% is assumed for the oral route.

No reprotoxic effects were observed in an OECD422 or OECD414 study up to the highest dose tested (150 and 230 mg/kg bw/d, respectively), Therfore, no reproduction DNELs needs to be derived.

 

Inhalation:The primary route of anticipated occupational exposure to 2-ethyl-4-methylimidazole is via skin contact. Given its low vapour pressure at room temperature (0.028 Pa), inhalation is not likely to occur. However, exposure to aerosols or droplets of an inhalable size cannot be excluded. Long-term inhalation toxicity data is not available and therefore route-to-route extrapolation is performed. An absorption of 100% is assumed for the inhalation route.

 

Dermal:Long-term dermal toxicity data is not available and therefore route-to-route extrapolation is performed. The long-term systemic DNEL was derived and additionally, due to the sensitizing effects of the substance, the long-term local DNEL.

For the derivation of the dermal DNELs the following considerations concerning dermal absorption were taken into account: 

A) The acute LD50 after intraperitoneal injection for NMRI and BI6 mice lies between 180 and 200 mg/kg bw. In the LLNA study CBA mice were exposed to 50 µL of 25% 2-ethyl-4-methylimidazole for three days. Since the animals weights about 20g, this dermal exposure is the equivalent of 625 mg/kg bw/d, but no mortality was observed. The penetration through the skin is therefore maximum 200 / 625 * 100 = 32%, but probably lower since the dermal LD50 will be higher than 625 mg/kg bw.

B) QSAR model DERMWIN (part of the model EPI suite) results in an estimated Kp = 0.00467 cm/hr. According to the user manual of the Danish QSAR database, May 2005 this indicates low dermal absorption (range: very low/low/moderate/high). 

The comparison of the effects after dermal absorption in the LLNA versus the acute LD50 after ip administration supports this assumption of a low dermal absorption. Therefore, in a Weight of Evidence the dermal absorption could be considered to be maximal 50 % of the oral absorption.

Long-term – dermal, local effects (based on LLNA test)

Description	Value	Remark
Step 1) Relevant dose-descriptor	NOEL 14.2%	EC3 = NOEL in human sensitization tests
Step 2) Modification of starting point	1 cm^2/ ear = 2 cm^2   25 µL / ear = 50µL = (50000 µg for density 1)   0.815	Area treated (1 cm2 = 1 mouse ear (ECHA Guidance Appendix R8.10 Skin sensitization)     Amount applied      Density of vehicle (olive oil:acetone 1:4, v/v)
Modified dose-descriptor	14.2 x 50000/2 x 0.815 / 100 = 2893 µg/cm^2
Step 3) Assessment factors
Vehicle or matrix effect	1	Uncertainty factor for matrix effects is considered to be included in the exposure estimation and, therefore, disregarded.
Exposure conditions	1	Uncertainty factor for differences in exposure conditions between animal experiment and human exposure situation is considered to be included in the exposure estimation and, therefore, disregarded.
Interspecies	1	EC3 = NOEL in human sensitization tests
Intraspecies	10	combined influence of genetic effects, sensitive subpopulations, inherent barrier function, age, gender, ethnicity
Exposure duration	1
Dose response	1
Quality of database	1
DNEL	Value
	2893 / (1 x 1 x1 x 10 x 1 x 1 x 1) = 2893 / 10 =289 µg/cm^2

 

Justification for the long-term, dermal, local DNEL:

An induction-specific DNEL was derived for skin sensitization according to Guidance on information requirements and chemical safety assessment, Chapter R.8 (ECHA, Nov 2012) based on the EC3 value from an LLNA study (2012). The EC3 value for2-Ethyl-4-methylimidazole, CAS 931-36-2was reported to be14.2 % (w/w) = 2893 µg/cm2, indicative of a sensitizer of weak potency (ECETOC 2003).

Interspecies

There are different views on the threshold derived from local lymph node data (EC3, EC1.5). Whereas the ECHA guidance considers it to be the LOAEL for induction (ECHA guidance R.8), a number of other organizations were able to empirically show that the EC3 closely correlates with the NOEL from human sensitization tests designed to confirm lack of induction (Api et al., 2006, Api et al., 2008, ECETOC TR87, 2003). Therefore, it seems appropriate to use the EC3 or EC1.5, expressed as dose per skin area, as a surrogate for the human sensitization threshold without the modification by uncertainty factors.

Intraspecies

It is recognized that a general DNEL must take into account that the threshold for skin sensitization varies between individuals. This may be due to differences in parameters such as genetic effects, sensitive subpopulations, inherent barrier function, age, gender, and ethnicity (Api et al., 2008). Whereas the latter three are recognized to have some effect on the sensitization threshold, it is generally recognized that genetic differences, the inherent barrier function and especially sensitive subpopulations play a major role Api et al., 2008). The barrier function of the skin may be compromised which in turn may lead to a greater susceptibility of the individual. At the same time the barrier function is thought to be very similar from infancy to adulthood. The influence of the genetic setting is not well understood, however, may be plausible in the light of the immunological effect under consideration. The term ‘sensitive subpopulations’ refers mostly to individuals who have previously been sensitized to other substances which may increase the susceptibility to further sensitizers (Api et al., 2006, Api et al., 2008). All of these effects make up the intraspecies factor and a factor of 10 is thought to adequately address the combined influence of these effects

 

Reference:

·    Api AM, Basketter DA, Cadby PA, Cano M-F, Graham E, Gerberick F, Griem P, McNamee P, Ryan CA, Safford B (2006). Dermal Sensitization Quantitative Risk Assessment (QRA) for fragrance ingredients. Technical dossier. March 15, 2006 (revised May 2006).

·    Api AM, Basketter, DA, Cadby PA, Cano M-F, Ellis G, Gerberick GF, Griem P, McNamee PM, Ryan CA, Safford R (2008). Dermal sensitization quantitative risk assessment (QRA) for fragrance ingredients.Reg Toxicol Pharmacol52: 3-23.

·          ECETOC (2003). Contact Sensitization: classification according to potency.Technical Report No. 87, April 2003.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.7 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

50

Modified dose descriptor starting point:

NOAEC

Value:

35 mg/m³

Explanation for the modification of the dose descriptor starting point:

NOAEC = NOAEL (90d, oral, rat) *abs oral/abs inhal /1.15 m3/kg bw = NOAEL /(2*1.15) (R.8.4.2)

AF for dose response relationship:

1

Justification:

GLP study according to OECD TG 408 with 3 doses

AF for differences in duration of exposure:

2

Justification:

Subchronic to chronic extrapolation

AF for interspecies differences (allometric scaling):

1

Justification:

No allometric scaling has to be applied in case of oral to inhalation route to route extrapolation.

AF for other interspecies differences:

2.5

Justification:

default

AF for intraspecies differences:

10

Justification:

default for general population

AF for the quality of the whole database:

1

Justification:

sufficient reliable data available

AF for remaining uncertainties:

1

Justification:

default

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

200

Modified dose descriptor starting point:

NOAEL

Value:

160 mg/kg bw/day

Explanation for the modification of the dose descriptor starting point:

NOAEL (90d, oral, rat) * abs. oral/abs. dermal = 80 mg/kg bw/d *0.5

AF for dose response relationship:

1

Justification:

GLP study according to OECD TG 408 with 3 doses

AF for differences in duration of exposure:

2

Justification:

Subchronic to chronic extrapolation

AF for interspecies differences (allometric scaling):

4

Justification:

default from rat to man

AF for other interspecies differences:

2.5

Justification:

default

AF for intraspecies differences:

10

Justification:

default for general population

AF for the quality of the whole database:

1

Justification:

sufficient reliable data available

AF for remaining uncertainties:

1

Justification:

default

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

289 µg/cm²

Most sensitive endpoint:

sensitisation (skin)

DNEL related information

DNEL derivation method:

other: see discussion

Overall assessment factor (AF):

10

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.4 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

200

Modified dose descriptor starting point:

NOAEL

Value:

80 mg/kg bw/day

Explanation for the modification of the dose descriptor starting point:

NOAEL (90d, oral, rat) = 80 mg/kg bw/d

AF for dose response relationship:

1

Justification:

GLP study according to OECD TG 408 with 3 doses

AF for differences in duration of exposure:

2

Justification:

Subchronic to chronic extrapolation

AF for interspecies differences (allometric scaling):

4

Justification:

default from rat to man

AF for other interspecies differences:

2.5

Justification:

default

AF for intraspecies differences:

10

Justification:

defaut for general population

AF for the quality of the whole database:

1

Justification:

sufficient reliable data available

AF for remaining uncertainties:

1

Justification:

default

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - General Population

Although there are no consumer uses, DNELs for the general population were derived. For point of departure of all derived DNELs and justification of long-term, dermal local DNEL see Discussion for worker DNELs.

Long-term – dermal, local effects (based on LLNA test)

Description	Value	Remark
Step 1) Relevant dose-descriptor	NOAEL 14.2%	EC3 = NOEL in human sensitization tests
Step 2) Modification of starting point	1 cm^2/ ear = 2 cm^2   25 µL / ear = 50µL = (50000 µg for density 1))   0.815	Area treated    Amount applied       Density of vehicle (olive oil:acetone 1:4, v/v)
Modified dose-descriptor	14.2 x 50000/2 x 0.815 / 100 = 2893 µg/cm^2
Step 3) Assessment factors
Vehicle or matrix effect	1	Uncertainty factor for matrix effects is considered to be included in the exposure estimation and, therefore, disregarded.
Exposure conditions	1	Uncertainty factor for differences in exposure conditions between animal experiment and human exposure situation is considered to be included in the exposure estimation and, therefore, disregarded.
Interspecies	1	Assessment factor for allometric scaling is not needed; empiral evidence shows that the EC3/EC1.6 closely correlates with the NOEL from human sensitization tests designed to confirm lack of induction.
Intraspecies	10	A factor of 10 is considered to adequately address the combined influence of factors influencing individual susceptibility.
Exposure duration	1
Dose response	1
Quality of database	1
DNEL	Value
	2893 / (1 x 1 x1 x 10 x 1 x 1 x 1) = 2893 / 10 =289 µg/cm^2