Methacrylic acid

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Effects on fertility

Description of key information

2-gen study (OECD 416) in rats, oral administration of the read-across substance MMA; NOAELs for systemic toxicity & fertility =  400 mg MMA/kg/d, equivalent to 344 mg MAA /kg/d (BASF; 2010)

Link to relevant study records

Reference

Endpoint:

two-generation reproductive toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

HYPOTHESIS FOR THE ANALOGUE APPROACH ACCORDING TO RAAF SCENARIO #1 (“Biotransformation to common compound”)
MAA and MMA share a common metabolic pathway: rapid enzymatic hydrolysis of MMA, the methanolic ester of MAA, leads to two primary metabolites in the human body, MAA and methanol. From this perspective, MMA can be seen as metabolic precursor of MAA and thus can be used to assess the systemic toxicity of MAA at different endpoints; the impact of methanol as potential confounding factor must however be considered for a read across on a high confidence level. This metabolic pathway widely is conservative in animals and humans so that animal models can be used for the hazard assessment.

SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
MMA as well as MAA are highly pure mono-constituent substances with typical concentrations ≥ 99 % purity. No relevant impurities are included and thus no consequences on the relevant endpoints are to be expected.

ANALOGUE APPROACH JUSTIFICATION
After being rapidly absorbed, the parent compound MMA, the methanolic ester of MAA, is hydrolysed rapidly to the two primary metabolites MAA and methanol by ubiquitous carboxylesterases in various tissues including liver and lung. The rapid hydrolysis of MMA was documented by Jones (2002) in rats, with a systemic half-life of 4.4 min, and Crout et al. (1979) in humans, below others (see chapter “Toxicokinetics”).
The further metabolism of MAA can be briefly described in such a way that MAA, after rapid reaction with the ubiquitous Coenzyme-A, forms Methacrylyl-CoA, a naturally occurring intermediate in the valine pathway. After further enzymatic activities, Methacrylyl-CoA joins the citrate cycle, with carbon dioxide and water being the final products (Jones, 2002; Rawn, 1983; Shimomura et al., 1994; Boehringer, 1992). The further metabolism of the alcohol metabolite is well known, with alcohol dehydrogenase and acetaldehyde dehydrogenase as key enzymes in the liver.
The impact of methanol on the toxicity profile of MMA has been assessed with the help of reliable studies of comparable test design to studies with MMA (see endpoint study summary). Here, it became obvious that the potential of methanol for systemic toxicity at this endpoint is so low that an impact of this metabolite on (potential) effects of MMA are irrelevant, considering the comparable tested dose levels in the MMA studies. The known, species-specific toxicity of methanol to humans that triggered acute toxic Cat 3 classifications is only exerted at concentrations which are much higher than those which can be achieved as a metabolite in studies with MMA at this endpoint, so this aspect is of no relevance for this endpoint.

According to the common assessment elements (CAE) and specific assessment elements of the RAAF Scenario #1 (SAE1), the read across approach can be justified with a high level of confidence as follows:

CAE-1 - Identity and characterisation of the source substance
Source and target substances are both mono-constituents with a high purity. Thus, both substances can be seen as well identified and characterized.
CAE-2 - Link of structural similarities and differences with the proposed prediction
With the same acyl group, the source and target substance share widely the same chemical structure. All properties related to this functional group are common to MMA and MAA. MMA represents the methanolic C1-ester of the MAA. Thus, the structural similarities between both substances provide a high level of confidence to this approach.
CAE-3 - Reliability and adequacy of the source study
The source study is a GLP guideline study of high reliability.
CAE-4 - Bias that influences the prediction
A potential bias can theoretically stem from the toxicity of the alcohol metabolite methanol. However, as mentioned above the toxic potential of methanol is so low for this endpoint that a bias can be excluded at the dose levels of the comparable studies with MMA.
--
SAE1-1 - Formation of common compound
MAA itself represents the common compound of both substances, after rapid hydrolysis of its methanolic ester MMA.
SAE1-2 - The biological targets for the common compound
In all studies with MMA and MAA that allow an assessment of systemic effects, unspecific toxicity was observed that is seen as bw effects. No specific target organs could be identified, presumably due to the rapid degradation by physiological pathways.
SAE1-3 - Exposure of the biological target to the common compound
MMA is rapidly absorbed and thus readily available systemically. In all further metabolic steps, there is no difference between MMA and MAA.
SAE1-4 - The impact of parent compounds
The capacity of carboxylesterases may become overloaded in case of very high doses of the parent ester MMA, especially after bolus dosing; then of the intact ester may theoretically lead to systemic effects. However, in this read across approach generally only studies with rather continuous dosing (inhalation or drinking water) were used, thus the impact of the parent ester MMA is considered as negligible.
SAE1-5 - Formation and impact of non-common compounds
See CAE-4

Reason / purpose for cross-reference:

read-across source

Key result

Dose descriptor:

NOEL

Remarks:

F0 systemic

Effect level:

43 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

food consumption and compound intake

Remarks on result:

other: calculated from a molar NOEL of 0.5 mMol/kg/d and a molar weight of 86 g MAA/mol

Key result

Dose descriptor:

NOEL

Remarks:

F1 systemic

Effect level:

129 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Remarks on result:

other: calculated from a molar NOEL of 1.5 mMol/kg/d and a molar weight of 86 g MAA/mol

Dose descriptor:

NOAEL

Remarks:

fertility

Generation:

F1

Effect level:

344 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

other: calculated from a molar NOAEL of 4 mMol/kg/d and a molar weight of 86 g MAA/mol

Dose descriptor:

NOAEL

Remarks:

developmental toxicity

Generation:

F1

Effect level:

344 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

other: calculated from a molar NOAEL of 4 mMol/kg/d and a molar weight of 86 g MAA/mol

Dose descriptor:

NOAEL

Remarks:

fertility

Generation:

F2

Effect level:

344

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

other: calculated from a molar NOAEL of 4 mMol/kg/d and a molar weight of 86 g MAA/mol

Dose descriptor:

NOAEL

Remarks:

developmental toxicity

Generation:

F2

Effect level:

344 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

other: calculated from a molar NOAEL of 4 mMol/kg/d and a molar weight of 86 g MAA/mol

Reproductive effects observed:

no

Conclusions:

A two-generation study in rats was performed with MMA, the metabolic precursor of MAA, according to OECD TG 416 and GLP  that can be used to assess the reproductive toxicity of MAA. While unspecific paternal effects were seen as reduced food consumption and partially as reduced body weights, there was no indication of reproductive or developmental toxicity.
The NOEL for general, systemic toxicity is 0.5 mMol/kg bw/d in F0 animals and 1.5 mMol/kg bw/d in F1 animals bw/d, corresponding to 43 mg MAA/kg/d for F0 and to 129 mg MAA/kg/d for F1 parental animals, respectively.
The NOAELs for fertility and developmental toxicity, for the F1 and F2 generation, is 4 mMol/kg bw/d, corresponding to 344 mg MAA/kg/d in this study. 
While these results reproductive toxicity were gained in a study with MMA, they can be transferred to MAA with a high confidence.

Executive summary:

A two-generation study in rats was performed with MMA, the metabolic precursor of MAA, according to OECD TG 416 and GLP  that can be used to assess the reproductive toxicity of MAA.

Methyl Methacrylate was administered to groups of 25 male and 25 female healthy young Wistar rats (P parental generation) as an aqueous preparation by stomach tube at dosages of 0; 50; 150 and 400 mg/kg body weight/day. At least 73 days after the beginning of treatment, P animals were mated to produce a litter (F1). Mating pairs were from the same dose group and F1 animals selected for breeding were continued in the same dose group as their parents.

Groups of 25 males and 25 females, selected from F1 pups to become F1 parental generation, were treated with the test substance at dosages of 0; 50; 150 and 400 mg/kg body weight/day post weaning, and the breeding program was repeated to produce F2 litter. The study was terminated with the terminal sacrifice of the F2 weanlings and F1 adult animals.

Control parental animals were dosed daily with the vehicle (1% Carboxymethylcellulose suspension in drinking water and four drops Cremophor EL and one drop hydrochloric acid).

 

The mid- and high-dose parental animals (400 mg/kg bw/d) showed clinical signs of systemic toxicity. The only relevant clinical observation was temporary salivation during a short period after dosing, which is considered to be test substance-induced. From the temporary, short appearance immediately after dosing it is likely, that this finding was induced by a bad taste of the test substance or local affection of the upper digestive tract. It is, however, not considered to be an adverse toxicologically relevant finding.

In the mid- and high-dose (150 and 400 mg/kg bw/d) P generation animals, dose-related intermittent reductions of food consumption were noted, either during premating, gestation and lactation phases of this study. Less significant changes were noted for the F1 generation animals where the effects were limited to the high-dose group.

High dose F1 parental males had statistically significant lower body weights during several study segments, which led to a statistically significant reduction of the mean terminal body weight resulting in secondary weight changes of brain.

High dose parental females had statistically significant lower body weights during the first weeks after weaning. This weight decrease during major phases of sexual maturation led to an apparent marginal delay of vaginal patency. This minor delay did, however, not result in any corroborative pathological findings nor did it adversly effect F1 female cyclicity, fertility and reproduction. Thus, an influence of the test substance on female sexual maturation is not assumed.

Pathological examinations revealed no test-substance-related changes in organ weights, gross lesions, changes in differential ovarian follicle counts or microscopic findings, apart from an increase in kidney and liver weights in male and female animals in both generations which is presumably related to the treatment. There was no histopathologic lesion observed, that could explain the weight increase. It is regarded to be an adaptive change, most likely caused by an increase in metabolic activity in the two organs, which does not lead to histopathologic findings. It is not regarded to be an adverse effect.

There were no indications from clinical examinations as well as gross and histopathology, that the administration of methyl methacrylate via the diet adversely affected the fertility or reproductive performance of the P or F1 parental animals up to and including a dose of 400 mg/kg bw/day. Estrous cycle data, mating behavior, conception, gestation, parturition, lactation and weaning as well as sperm parameters, sexual organ weights and gross and histopathological findings of these organs (including differential ovarian follicle counts in the F1 females) were comparable between the rats of all test groups and ranged within the historical control data of the test facility.

All data recorded during gestation and lactation in terms of embryo-/fetal and pup development gave no indications for any developmental toxicity in the F1 and F2 offspring up to a dose level of 400 mg/kg bw/day. Up to this dose level, the test substance did not adversely influence pup viability and pup body weights. Sex ratio and sexual maturation was not directly affected at any dose level, inclusive the high-dose group (400 mg/kg bw/day).

 

Conclusion: The NOEL for general, systemic toxicity is 50 mg MMA/kg bw/day in F0 animals, corresponding to 0.5 mMol/kg bw/d, and 150 mg MMA/kg bw/day in F1 animals, corresponding to 1.5 mMol/kg bw/d, respectively, based on effects on food consumption (F0 & F1) and/ or body weight (F1) that were considered as treatment-related but not adverse. Considering the molar weight of MAA, these levels corresponds to 43 mg MAA/kg/d for F0 and to 129 mg MAA/kg/d for F1 parental animals, respectively.

The NOAELs for fertility and developmental toxicity, for the F1 and F2 generation, is 400 mg MMA/kg bw/day, the highest dose tested, corresponding to 4 mMol/kg bw/d or 344 mg MAA/kg/d. 

While these results reproductive toxicity were gained in a study with MMA, they can be transferred on molar level to MAA with a high confidence.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

344 mg/kg bw/day

Species:

rat

Quality of whole database:

GLP guideline study & read across with high confidence -> high quality of the database

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Data availability

There is no reliable study on reproductive toxicity available for MAA. Relevant information for hazard assessment is coming from the methanolic ester of MAA, Methyl Methacrylate (MMA), namely from a 2-generation reproductive toxicity study on MMA by the oral route.

MMA has been shown by Jones (2002, see chapter “Toxicokinetics”) to hydrolyse within <5 min by ubiquitous carboxylesterases to MAA and Methanol, so that MMA can be understood as metabolic precursor of MAA. Based on the available toxicokinetic data, studies with MMA can be used for read across to assess systemic effects of MAA including reproductive toxicity with a high level of confidence. This is especially true when adverse effect levels of the second primary metabolite, Methanol, are higher than the parent ester MMA (i.e., a potential impact from Methanol can be excluded) so that adverse effects can be exclusively related to MAA.

 

Non-human data

MMA was administered in an OECD TG 416 oral two-generation reproduction toxicity study to groups of 25 male and 25 female healthy young Wistar rats (F0 parental generation) as an aqueous preparation by stomach tube at dosages of 0; 50; 150 and 400 mg/kg body weight/day (BASF 2010). At least 73 days after the beginning of treatment, F0 animals were mated to produce a litter (F1). Mating pairs were from the same dose group and F1 animals selected for breeding were continued in the same dose group as their parents. Groups of 25 males and 25 females, selected from F1 pups to become F1 parental generation, were treated with the test substance at dosages of 0; 50; 150 and 400 mg/kg body weight/day post weaning, and the breeding program was repeated to produce F2 litter. The study was terminated with the terminal sacrifice of the F2 weanlings and F1 adult animals. Control parental animals were dosed daily with the vehicle (1% CMC suspension in drinking water).

 

The health state of the parents and the pups, respectively, was checked each day, and parental animals were examined for their mating and reproductive performances. Food consumption of the F0 and F1 parents was determined regularly once weekly during premating and during gestation and lactation periods. In general, body weights of F0 and F1 parents were determined once weekly. However, during gestation and lactation F0/F1 females were weighed on gestation days (GD) 0, 7, 14 and 20 and on postnatal days (PND) 0, 1, 4, 7, 14 and 21. Estrous cycle data were evaluated for F0 and F1 generation females over a three-week period prior to mating until evidence of mating occurred.  Moreover, the estrous stage of most females was determined on the day of scheduled sacrifice. The F1 and F2 pups were sexed on PND 0 and weighed on PND 1, 4, 7, 14 and 21. Their viability was recorded. At necropsy, all pups were examined macroscopically (including weight determinations of brain, spleen and thymus in one pup/sex/litter). Date of sexual maturation (day of balanopreputial separation/vaginal opening) of all F1 pups selected to become F1 parental generation was recorded. Various sperm parameters (motility, sperm head count, morphology) were assessed in F0 and F1 generation males at scheduled sacrifice or after appropriate staining. All F0 and F1 parental animals were assessed by gross pathology (including weight determinations of several organs) and subjected  to an extensive histopathological examination, special attention being paid to the organs of the reproductive system. A quantitative assessment of primordial and growing follicles in the ovaries was performed for all control and high-dose F1 parental females.

 

The only relevant clinical observation was temporary salivation during a short period of maximum 15 min after dosing of the 400 mg/kg bw/d dosing, which is considered to be test substance-induced. From the temporary, short appearance immediately after dosing it is likely, that this finding was induced by a bad taste of the test substance or local affection of the upper digestive tract. It is, however, not considered to be an adverse toxicologically relevant finding. In the mid- and high-dose (150 and 400 mg/kg bw/d) F0 generation animals, dose-related intermittent reductions of food consumption were noted, either during premating, gestation and lactation phases of this study. Less significant changes were noted for the F1 generation animals where the effects were limited to the 400 mg/kg bw/d group.

 

High dose F1 parental animals had statistically significantly lower body weights during several study segments, which led to a statistically significant reduction of the mean terminal body weight resulting in secondary weight changes of brain. The most distinct reductions of food consumption occurred at the beginning of the study and were more pronounced in the F0 generation than in the F1. It is considered that this effect was caused by  the pungent odour of MMA (odour threshold 0.5 – 1.5 ppm), rather than any substance-related systemic toxicity (cf. Borzelleca et al., 1964). Thus, there is evidence from the present and previous studies that in the absence of any clinical, clinical pathological and pathological signs of systemic toxicity it is likely that the most likely reason for the reduced body-weight gain in these animals is reduced food consumption due to reduced appetite. In conclusion, the reduced food consumption and body weight gain are considered as treatment-related effects, which limited the applicable dose of the test compound. They are however not regarded as any true systemic toxicity because no accompanying clinical, clinical pathological and pathological signs were noted in previous and the present studies.

 

Pathological examinations revealed no test-substance-related changes in organ weights, gross lesions, changes in differential ovarian follicle counts or microscopic findings, apart from an increase in kidney and liver weights in male and female animals in both generations which is presumably related to the treatment. There was no histopathologic lesion observed, that could explain the weight increase. It is regarded to be an adaptive change, most likely caused by an increase in metabolic activity in the two organs, which does not lead to histopathologic findings. It is not regarded to be an adverse effect. There were no indications from clinical examinations as well as gross and histopathology, that the oral administration of MMA adversely affected the fertility or reproductive performance of the F0 or F1 parental animals up to and including a dose of 400 mg/kg bw/day. Estrous cycle data, mating behavior, conception, gestation, parturition, lactation and weaning as well as sperm parameters, sexual organ weights and gross and histopathological findings of these organs (including differential ovarian follicle counts in the F1 females) were comparable between the rats of all test groups and ranged within the historical control data of the test facility.

 

All data recorded during gestation and lactation in terms of embryo-/foetal and pup development gave no indications for any developmental toxicity in the F1 and F2 offspring up to a dose level of 400 mg/kg bw/day. Up to this dose level, the test substance did not adversely influence pup viability and pup body weights. Sex ratio and sexual maturation was not directly affected at any dose level, inclusive the high-dose group (400 mg/kg bw/day).

 

The NOAEL for fertility and reproductive performance for the P and F1 parental rats was determined to be 400 mg/kg bw/day, the highest dose tested. The NOAEL for developmental toxicity, in the F1 and F2 progeny, of the test substance was determined to be 400 mg/kg bw/day, the highest dose tested. There were no signs of systemic toxicity other than reduced body weight gain associated with reduced food consumption, presumably due to bad palatability (NOEL 50 mg/kg bw/day for the P and F1 parental rats and LOEL of 150 mg/kg bw/day in the P parental females).

 

Considering the molecular weights of MMA (100 g/mol) and MAA (86 g/mol), the general NOAEL in this study of 400 mg MMA/kg bw/d corresponds to 4 mM MMA/kg bw/d which is equivalent to a NOAEL of 344 mg MAA/kg bw/d.

 

The impact of Methanol, CAS 67-56-1, as further primary metabolite, on the reproductive toxicity hazard profile of MMA can be assessed with the help of an older 2-generation inhalation study in rats (NEDO, 1987, as mentioned in the WHO EHC report #196, 1997). Here, Fischer-344 rats were exposed to up to 1300 mg/m3 (1000 ppm) in an unusual harsh exposure regime of 20 h/d and 7 d/week. A concentration of 1300 mg/m3 (1000 ppm) was found to be the NOAEC in absence of relevant effects related to fertility. When adopted to the standard exposure regimes of, the reproductive NOAEC of 1000 ppm of Methanol corresponds to approx. 39 mMol/kg/d (according to Gelbe et al., 2017) which indicates that Methanol does not contribute to potential effects of MMA when MMA is tested up to 4 mMol/kg/d (as highest dose tested).

 

Human data

No reliable data available.

Effects on developmental toxicity

Description of key information

Developmental toxicity study comp. OECD 414, inhalation, rats (Saillenfait 1999)

NOAEC maternal = 200 ppm (716 mg/m3)

NOAEC developmental up to 300 ppm (1076 mg/m³), equivalent to 3.6 mM/kg/d or
312 mg MAA/kg/d

 

Developmental toxicity study acc. OECD 414 oral administration of the read-across substance MMA, rabbits (BASF 2009)

NOAEL maternal = nominal 450 mg MMA/kg/d; actual 406 mg MMA/kg/d

NOAEL developmental = nominal 450 mg MMA/kg/d; actual 406 mg MMA/kg/d, equivalent to 4.1 mM MMA/kg/d, and finally to 345 mg MAA/kg/d

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

HYPOTHESIS FOR THE ANALOGUE APPROACH ACCORDING TO RAAF SCENARIO #1 (“Biotransformation to common compound”)
MAA and MMA share a common metabolic pathway: rapid enzymatic hydrolysis of MMA, the methanolic ester of MAA, leads to two primary metabolites in the human body, MAA and methanol. From this perspective, MMA can be seen as metabolic precursor of MAA and thus can be used to assess the systemic toxicity of MAA at different endpoints; the impact of methanol as potential confounding factor must however be considered for a read across on a high confidence level. This metabolic pathway widely is conservative in animals and humans so that animal models can be used for the hazard assessment.

SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
MMA as well as MAA are highly pure mono-constituent substances with typical concentrations ≥ 99 % purity. No relevant impurities are included and thus no consequences on the relevant endpoints are to be expected.

ANALOGUE APPROACH JUSTIFICATION
After being rapidly absorbed, the parent compound MMA, the methanolic ester of MAA, is hydrolysed rapidly to the two primary metabolites MAA and methanol by ubiquitous carboxylesterases in various tissues including liver and lung. The rapid hydrolysis of MMA was documented by Jones (2002) in rats, with a systemic half-life of 4.4 min, and Crout et al. (1979) in humans, below others (see chapter “Toxicokinetics”).
The further metabolism of MAA can be briefly described in such a way that MAA, after rapid reaction with the ubiquitous Coenzyme-A, forms Methacrylyl-CoA, a naturally occurring intermediate in the valine pathway. After further enzymatic activities, Methacrylyl-CoA joins the citrate cycle, with carbon dioxide and water being the final products (Jones, 2002; Rawn, 1983; Shimomura et al., 1994; Boehringer, 1992). The further metabolism of the alcohol metabolite is well known, with alcohol dehydrogenase and acetaldehyde dehydrogenase as key enzymes in the liver.
The impact of methanol on the toxicity profile of MMA has been assessed with the help of reliable studies of comparable test design to studies with MMA (see endpoint study summary). Here, it became obvious that the potential of methanol for systemic toxicity at this endpoint is so low that an impact of this metabolite on (potential) effects of MMA are irrelevant, considering the comparable tested dose levels in the MMA studies. The known, species-specific toxicity of methanol to humans that triggered acute toxic Cat 3 classifications is only exerted at concentrations which are much higher than those which can be achieved as a metabolite in studies with MMA at this endpoint, so this aspect is of no relevance for this endpoint.

According to the common assessment elements (CAE) and specific assessment elements of the RAAF Scenario #1 (SAE1), the read across approach can be justified with a high level of confidence as follows:

CAE-1 - Identity and characterisation of the source substance
Source and target substances are both mono-constituents with a high purity. Thus, both substances can be seen as well identified and characterized.
CAE-2 - Link of structural similarities and differences with the proposed prediction
With the same acyl group, the source and target substance share widely the same chemical structure. All properties related to this functional group are common to MMA and MAA. MMA represents the methanolic C1-ester of the MAA. Thus, the structural similarities between both substances provide a high level of confidence to this approach.
CAE-3 - Reliability and adequacy of the source study
The source study is a GLP guideline study of high reliability.
CAE-4 - Bias that influences the prediction
A potential bias can theoretically stem from the toxicity of the alcohol metabolite methanol. However, as mentioned above the toxic potential of methanol is so low for this endpoint that a bias can be excluded at the dose levels of the comparable studies with MMA.
--
SAE1-1 - Formation of common compound
MAA itself represents the common compound of both substances, after rapid hydrolysis of its methanolic ester MMA.
SAE1-2 - The biological targets for the common compound
In all studies with MMA and MAA that allow an assessment of systemic effects, unspecific toxicity was observed that is seen as bw effects. No specific target organs could be identified, presumably due to the rapid degradation by physiological pathways.
SAE1-3 - Exposure of the biological target to the common compound
MMA is rapidly absorbed and thus readily available systemically. In all further metabolic steps, there is no difference between MMA and MAA.
SAE1-4 - The impact of parent compounds
The capacity of carboxylesterases may become overloaded in case of very high doses of the parent ester MMA, especially after bolus dosing; then of the intact ester may theoretically lead to systemic effects. However, in this read across approach generally only studies with rather continuous dosing (inhalation or drinking water) were used, thus the impact of the parent ester MMA is considered as negligible.
SAE1-5 - Formation and impact of non-common compounds
See CAE-4

Reason / purpose for cross-reference:

read-across source

Species:

rabbit

Dose descriptor:

NOAEL

Remarks:

maternal

Effect level:

349 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other:

Remarks on result:

other: calculated from a molar NOAEL of 4.1 mMol/kg/d and a molar weight of 86 g MAA/mol

Dose descriptor:

NOEL

Remarks:

maternal

Effect level:

35 mg/kg bw/day (actual dose received)

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Remarks on result:

other: calculated from a molar NOEL of 0.41 mMol/kg/d and a molar weight of 86 g MAA/mol

Abnormalities:

no effects observed

Dose descriptor:

NOAEL

Effect level:

349 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse fetal findings of toxicological relevance were evident at any dose

Remarks on result:

other: calculated from a molar NOAEL of 4.1 mMol/kg/d and a molar weight of 86 g MAA/mol

Abnormalities:

no effects observed

Developmental effects observed:

not specified

Conclusions:

This study was performed according to OECD TG 414 and in compliance with GLP. Rabbits were orally exposed to methyl methacrylate, the metabolic precursor of MAA. This study can be used to assess prenatal developmental effects of MAA in non-rodent species. 
The NOEL for maternal toxicity is 0.41 mMol/kg bw/d (actual received) on molar level or 35 mg MAA/kg bw/d by consideration of the molar weight of 86 g MAA/mol, based on food consumption and body weight effects that are considered as treatment-related but not as true adverse systemic effects. The NOAEL for maternal toxicity is 4.1 mMol/kg bw/d (actual received) on molar level or 406 mgMAA/kg bw/d, in absence of adverse systemic effects.
The NOAEL for prenatal developmental toxicity is 4.1 mMol/kg bw/d (actual received) on molar level or 406 mgMAA/kg bw/d, in absence of developmental effects.
While these results were gained in a study with MMA, they can be transferred to MAA by read across with a high confidence.

Executive summary:

The study was performed according to OECD TG 414 and in compliance with GLP. Rabbits were orally exposed to methyl methacrylate, the metabolic precursor of MAA. This study can be used to assess prenatal developmental effects of MAA in non-rodent species. 

The test substance was administered as an aqueous preparation to 25 inseminated female Himalayan rabbits by stomach tube at doses of nominal 50; 150 and 450 mg/kg bw/d on gestation days (GD) 6 through GD 28 (corresponding to 41, 132 and 406 mg/kg bw/d actual received).

At terminal sacrifice on GD 29, 24-25 females per group had implantation sites.

The following test substance-related adverse effects/findings were noted:

Test group 3 (450 mg/kg bw/day):

-        Reduced food consumption (-18%) and body weight gain (-31%)

-        No test substance-related adverse effects on gestational parameters or fetuses

 

Test group 2 (150 mg/kg bw/day):

-        Reduced food consumption (-13%) and body weight gain (-27%)

-        No test substance-related adverse effects on gestational parameters or fetuses

 

Test group 1 (50 mg/kg bw/day):

-        No test substance-related adverse effects on does, gestational parameters or fetuses

 

In conclusion, the no observed effect level (NOEL) for maternal toxicity is nominal 50 mg/kg bw/d or 41 mg/kg bw/d actual received, based on food consumption and body weight effects that are considered as treatment-related but not as true adverse systemic effects. The no observed adverse effect level (NOAEL) for maternal toxicity is nominal 450 mg/kg bw/d or 406 mg/kg bw/d actual received, in absence of adverse systemic effects. These maternal effect levels corresponds to 0.41 mMol/kg bw/d and 4.1 mMol/kg bw/d on molar level or 35 mg MAA/kg bw/d and 349 mg MAA/kg bw/d, respectively, by consideration of the molar weight of 86 g MAA/mol.

The NOAEL for prenatal developmental toxicity is 450 mg/kg bw/d. No adverse fetal findings of toxicological relevance were evident at any dose. This developmental NOAEL corresponds to 4.1 mMol/kg bw/d on molar level and thus 349 mg MAA/kg bw/d.

While these results were gained in a study with MMA, they can be transferred to MAA by read across with a high confidence.

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

before 27th June 2018

Deviations:

no

GLP compliance:

not specified

Limit test:

no

Specific details on test material used for the study:

Methacrylic acid (CAS: 79-41-4)
Purity: 98 %
Obtained from Fluka Chemie AG

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

Nulliparous female Sprague-Dawley rats, weighing 180-200  grams.obtained from IFFA Credo Breeding Labs. AGE at Start of Test: sexually mature females; age not specified. Mated females were  housed inclear polycarbonate cages with stainless steel wire lids and  hardwood shavings for bedding. Food and water available adlibitum except  during exposures.
12 hours light-dark photocycle
Acclimatization of test animals: 2 weeks

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

 Exposures were whole  body and conducted in a 200 L chamber. Chamber temperature was 23°C +/- 2 °C, and the relative humidity was 50% +/- 5%. Air was passed through a heated  bubbler containing test material. The vaporized material was then  introduced into the exposure chambers.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Concentrations were determined 3 times at regular intervals during each 6 hr exposure by collecting
the material and analyzing against a standard using GC.
Target concentrations [ppm] Analytical concentrations [ppm]
mean +/- SD
--------------------------------------------------------------------------------
50 55.3 +/- 8.1
100 101.5 +/-16.9
200 207.3 +/- 24.7
300 316.0 +/- 36.7
--------------------------------------------------------------------------------

Details on mating procedure:

2-3 females were caged with one male rat for mating. The  onset of gestation was based upon the presence of sperm in the vaginal  smear and this was designated gestation day 0. After confirmation of  mating, females werere turned to an individual cage. 

Duration of treatment / exposure:

6 hours per day

Frequency of treatment:

day 6 to 20 of gestation

Duration of test:

Mated females were exposed 6 hr/day on days 6 through  20 of gestation.

Dose / conc.:

50 ppm

Remarks:

corresponds to 179 mg/m3

Dose / conc.:

100 ppm

Remarks:

corresponds to 358 mg/m3

Dose / conc.:

200 ppm

Remarks:

corresponds to 716 mg/m3

Dose / conc.:

300 ppm

Remarks:

corresponds to 1076 mg/m3

No. of animals per sex per dose:

23 to 27 female rats were bred resulting in 22 to 23 pregnant rats used for experiment.

Control animals:

other: yes, concurrently exposed to filtered room air

Maternal examinations:

BODY WEIGHT: Yes
- Time schedule for examinations: GDs 0, 6, 13 and 21
FOOD CONSUMPTION: Yes
- Time schedule for examinations: GDs 6-13 and 13-21

Ovaries and uterine content:

Uterine content was examined after termination: Yes
Examinations included:
- uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: No data
- Number of viable and dead fetuses: Yes
At necropsy, the uterine horns and ovaries were exposed to count the C.L., implantation sites, re
sorption sites, and viable and dead fetuses. FERTILITY AND REPRODUCTIVE PERFOR
MANCE: The following data were recorded for each group of numbers of CL, and implantation
sites o number of resorptions and viable and dead fetuses. O mean fetal body weights o fe
tuses examined for gross malformations and skeletal abnormalities of sex and of fetuses.

Fetal examinations:

- External examinations: Yes
- Soft tissue examinations: Yes
- Skeletal examinations: Yes
- Head examinations: No data
Live fetuses were weighed, sexed, and examined for external anomalies. 50% of the live fetuses from
each litter were preserved in Bouin's solution and examined for internal soft-tissue changes. The remaining fetuses (50%) were fixed in ethanol (70%), eviscerated and then processed for skeletal stai
ning with alizarin red S.

Statistics:

The number of corpora lutea, implantation sites, and live fetuses, maternal food consumption and various body weights were analyzed by ANOVA, followed by Dunnett's
test. The percentage of non-live implant, resorptions, and males and the proportion of fetuseswith alterations in each litter were evaluated by Kruskal-Walles test followed by Dixon-Massey test
. Rates of pregnancy and percentage of litters with any malformations or external, visceral, or skeletal variations were analyzed using Fisher's test. Where appropriate, least squares analysis was per
formed. The level of significance was p < 0.05. The litter was used as the basis of analysis of fetal variables.

Indices:

Pre- and postimplantation loss; live birth index

Clinical signs:

not specified

Dermal irritation (if dermal study):

not specified

Mortality:

no mortality observed

Description (incidence):

All animals survied the exposure.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Absolute weight gain was significantly reduced at 300 ppm.

Change in weight during gestation in Sprague-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation and euthanized on day 21:
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Concentrations No of dams Mean Body weight [g] +/- SD Mean body weight gain on GD [g] Mean absolute weight gain [g]
[ppm], 6 h/day on GD 6 6 - 13 13 - 21 6 - 21
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0 23 276 +/- 19 32 +/- 9 109 +/- 32 141 +/- 36 36 +/- 13
50 22 278 +/- 18 32 +/- 8 115 +/- 13 147 +/- 15 35 +/- 11
100 22 283 +/- 19 34 +/- 7 110 +/- 19 144 +/- 23 36 +/- 14
200 22 284 +/- 22 29 +/- 8 107 +/- 20 136 +/- 24 32 +/- 13
300 23 276 +/- 16 20 +/- 7** 91 +/- 26* 111 +/- 29** 12 +/- 14**
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*, ** Denote significant differences from the control (0 ppm), p < 0.05 and p < 0.01, respectively.

Mean absolute weight gain: Mean body weight gain corrected by gravid uterine weight

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Fopod consumption was reduced at 300 ppm.
Food consumption of Sprague-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation and euthanized on day 21:
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Concentrations No of dams Mean food consumption [g/dam/day] on GD
[ppm], 6 h/day 6 - 13 13 - 21 6 - 21
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0 23 23 +/- 2 27 +/- 3 25 +/- 2
50 22 24 +/- 1 28 +/- 2 26 +/- 2
100 22 24 +/- 3 28 +/- 3 26 +/- 3
200 22 22 +/- 2 27 +/- 2 25 +/- 2
300 23 20 +/- 2** 24 +/- 2** 22 +/- 26*
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*, ** Denote significant differences from the control (0 ppm), p < 0.05 and p < 0.01, respectively

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Other effects:

not specified

Number of abortions:

no effects observed

Description (incidence and severity):

There were no abortions reported.

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

There were no significant changes in number of implantations across control and exposed groups.

Total litter losses by resorption:

no effects observed

Description (incidence and severity):

Total litter loss by resoprtion was not reported.

Early or late resorptions:

no effects observed

Description (incidence and severity):

The number of early and late resorptions was unaffected by treatment.

Dead fetuses:

no effects observed

Description (incidence and severity):

No number of dead fetuses was not reported.

Changes in pregnancy duration:

not specified

Description (incidence and severity):

In the OECD 414, a Caesarian section on GD 21 is performed.

Changes in number of pregnant:

no effects observed

Description (incidence and severity):

The number of pregnant females is comparable to the control.

Other effects:

not specified

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
All animals survived the exposure. Exposure to 300 ppm led to significant decreases in maternal weight gain and food consumption throughout exposure. Absolute weight gain was significantly reduced at 300 ppm.

Dose descriptor:

NOAEL

Effect level:

200 ppm

Based on:

test mat.

Basis for effect level:

body weight and weight gain

Remarks on result:

other: corresponds to 716 mg/m³

Abnormalities:

no effects observed

Fetal body weight changes:

no effects observed

Description (incidence and severity):

The fetal body weight was unaffected by treatment.

Reduction in number of live offspring:

no effects observed

Description (incidence and severity):

Reproductive parameters in Sprague-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation and euthanized on day 21:
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Concentrations No of litters No. of live fetuses per litter
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0 22 14.73 +/- 3.92
50 22 14.86 +/- 1.93
100 22 14.05 +/- 3.17
200 22 13.77 +/- 3.99
300 22 14.05 +/- 3.76

Changes in sex ratio:

no effects observed

Description (incidence and severity):

Reproductive parameters in Sprague-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation and euthanized on day 21:
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Concentrations No of litters Average fetal body weight [g/per litter]
[ppm], 6 h/day All Males Females
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0 22 5.71 +/- 0.56 5.86 +/- 0.57 5.42 +/- 0.37
50 22 5.66 +/- 0.27 5.82 +/- 0.32 5.49 +/- 0.27
100 22 5.79 +/- 0.30 5.92 +/- 0.32 5.62 +/- 0.32
200 22 5.76 +/- 0.47 5.92 +/- 0.47 5.54 +/- 0.45
300 22 5.67 +/- 0.49 5.71 +/- 0.34 5.54 +/- 0.52
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Changes in litter size and weights:

not specified

Description (incidence and severity):

Litter size and weights were not reported.

Changes in postnatal survival:

not specified

Description (incidence and severity):

The pups were euthanised before birth.

External malformations:

no effects observed

Description (incidence and severity):

No significant increase of external fetal malformations was observed after exposure to methacrylic acid. There was no difference between the control and exposed groups.
Description please see attached document (Incidence of malformations and variations in fetuses of Spraque-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation).

Skeletal malformations:

no effects observed

Description (incidence and severity):

No significant increase of skeletal fetal malformations was observed after exposure to methacrylic a cid. There was no difference between the control and exposed groups.
Description please see attached document (Incidence of malformations and variations in fetuses of Spraque-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation).

Visceral malformations:

no effects observed

Description (incidence and severity):

No significant increase of visceral fetal malformations was observed after exposure to methacrylic a cid. There was no difference between the control and exposed groups.
Description please see attached document (Incidence of malformations and variations in fetuses of Spraque-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation).

Other effects:

not specified

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
There were no significant changes in number of implantations and live fetuses, in the incidence of non-live implants and sorptions, or in fetal weights across groups. One fetus of 200 ppm and two of the 300 ppm group showed different types of malfomations. There was no consistent pattern of changes to suggest any treatment-related effects. The difference of fetuses with external, visceral, and skeletal variations did not differ between the control and the treated groups. No significant increase in embryo/fetal lethality or fetal malformations were observed after exposure to methacrylic acid. While maternal toxicity was observed, methacrylic acid caused no  evidence of developmental toxicity up to 300 ppm.

Dose descriptor:

NOAEL

Effect level:

>= 300 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no effects observed

Remarks on result:

other: corresponds to 1076 mg/m³

Abnormalities:

no effects observed

Developmental effects observed:

no

	Methacylic acid (Saillenfait 1999, OECD 414 rat inhalativ 6 h/day)
	control	50 ppm (corresponding 179 mg/m³)	100 ppm(corresponding 358 mg/m³)	200 ppm (corresponding 716 mg/m³)	300 ppm (corresponding 1076 mg/m³)
number of pregnant/ non pregnant dams	25 (total) / 23 (= 92%) pregnant / 2non pregnant	25 (total) / 22 (=88%) pregnant / 3 non pregnant	26 (total) / 23 (=84.6%) pregnant / 3 non pregnant	25 (total) / 22 (= 88%) pregnant / 3 non pregnant	26 (total) / 23 (= 88.5%) pregnant / 3 non pregnant
number of dams with abortions/ early deliveries/ stillbirths/ resorptions and/or dead fetuses	number of abortions not explicitly specified early deliveries were not reported (assumed to be 0) number of stillbirth were not reported (assumed to be 0) number of resorptions: 8.96 +/- 20.73	number of abortions not explicitly specified early deliveries were not reported (assumed to be 0) number of stillbirth were not reported (assumed to be 0) number of resorptions: 3.22 +/- 3.34	number of abortions not explicitly specified early deliveries were not reported (assumed to be 0) number of stillbirth were not reported (assumed to be 0) number of resorptions: 6.76 +/- 8.14	number of abortions not explicitly specified early deliveries were not reported (assumed to be 0) number of stillbirth were not reported (assumed to be 0) number of resorptions: 5.67+/- 12.77	number of abortions not explicitly specified early deliveries were not reported (assumed to be 0) number of stillbirth were not reported (assumed to be 0) number of resorptions: 10.61 +/- 21.45
Preimplantation loss (as no individual data is given in the publication, the preimplantation loss is calculated based on the means of number of corpora lutea and number of implantation sites)	12.55 mean	4.6 mean	7.58 mean	12.01 mean	9.81 mean
Postimplantation loss (as no individual data is given in the publication, the postimplantation loss is calculated based on the means of number of implantation sites and number of live offspring)	1.21 mean	3.26 mean	6.33 mean	4.11 mean	2.63 mean
Mean Body weight [g] on GD6	276 +/- 19 SD	278 +/- 18 SD	283 +/- 19 SD	284 +/- 22 SD	276 +/- 16 SD
Mean Body weight change [g]	141 +/- 36 on GD 6-21	147 +/- 15 on GD 6-21	144 +/- 23 on GD 6-21	136 +/- 24 on GD 6-21	111 +/- 29** on GD 6-21 significant different from the control (0 ppm)
mean gravid uterine weight including optionally body weight change corrected for gravid uterine weight (differenece between body weight gain from GD 6-21 and absolute body weight gain)	105 g mean	112 g mean	108 g mean	104 g mean	99 g mean
mean number and percent of live offspring	14.73 live pups/litter percentage not specified	14.86 live pups/litter percentage not specified	14.05 live pups/litter percentage not specified	13.77 live pups/litter percentage not specified	14.05 live pups/litter percentage not specified
mean foetal/ pup weight by sex and sexes combined	5.71 mean (g/litter) 5.86 males (g/litter) 5.42 females (g/litter)	5.66 mean (g/ litter) 5.82 males (g/litter) 5.49 females (g/litter)	5.79 mean (g/litter) 5.92 males (g/litter) 5.62 females (g/litter)	5.76 mean (g/litter) 5.92 males (g/litter) 5.54 females (g/litter)	5.67 mean (g/litter) 5.71 males (g/litter) 5.54 females (g/litter)
number and percent of foetuses and litters with malformations (including runts) and/ or variations	number of malformations:- litter affected: - number of variations: 37/324 or 11.4% litter affected: 21/22 (95.4%)	number of malformations:- litter affected: - number of variations: 35/327 or 10.7% litter affected: 20/22 (90.9%)	number of malformations:- litter affected: - number of variations: 41/309 or 13.3% litter affected:15/22 (68.2%)	number of malformations: 1/303 or litter affected: 1/22 or 4.5% number of variations: 29/303 or 9.6% litter affected: 16/22 (72.7%)	number of malformations: 2/309 or 0.6% litter affected: 2/22 or 9.0% number of variations: 39/309 or 12.6% litter affected: 16/22 (72.7%)
description and incidences of malformations and main variations (and/ or retardation	(detailed information see attached document to the IUCLID entry of this study (Incidence of Malformations and variations in fetuses of Spraque- Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation))	(detailed information see attached document to the IUCLID entry of this study (Incidence of Malformations and variations in fetuses of Spraque-Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation))	(detailed information see attached document to the IUCLID entry of this study (Incidence of Malformations and variations in fetuses of Spraque- Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation))	(detailed information see attached document to the IUCLID entry of this study (Incidence of malformations and variations in fetuses of Spraque- Dawley rats Inhaling Methacrylic acid on days 6 to 20 of gestation))	(detailed information see attached document to the IUCLID entry of this study (Incidence of malformationsand variations in fetuses of Spraque- Dawley rats inhaling Methacrylic acid on days 6 to 20 of gestation))

Conclusions:

Using a valid scientific method, no significant increase in embryo/fetal lethality or fetal malformations were observed after exposure to methacrylic acid. While maternal toxicity was observed, methacrylic acid caused no  evidence of developmental toxicity up to 300 ppm.

Executive summary:

In an OECD 414 prenatal developmental toxicity study using whole body inhalation methacrylic acid at test concentrations of 50, 100, 200 and 300 ppm, corresponding to 179, 358, 716 and 1076 mg/m³ methacylic acid did not produce any embryo - or foetal lethality, nor fetal malformations, despite overt maternal toxicity (decreased body weight and feed consumption). The NOEC (teratogenicity) was considerd to be 300 ppm (1076 mg/m³).

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

345 mg/kg bw/day

Species:

rabbit

Quality of whole database:

GLP guideline study & read across with high confidence -> high quality of the database

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

300 ppm

Species:

rat

Quality of whole database:

Reliable study comparable to guideline -> high quality of the database

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Data availability

There is a reliable study on developmental toxicity in rodents available for MAA using the inhalative route. Relevant information for the hazard assessment of non-rodents is coming from the methyl ester of MAA, Methyl Methacrylate (MMA), namely from an oral gavage study on MMA in rabbits.

MMA has been shown by Jones (2002, see chapter “Toxicokinetics”) to hydrolyse within <5 min by ubiquitous carboxylesterases to MAA and Methanol, so that MMA can be understood as metabolic precursor of MAA. Based on the available toxicokinetic data, studies with MMA can be used for read across to assess systemic effects of MAA including developmental toxicity with a high level of confidence. This is especially true when adverse effect levels of the second primary metabolite, Methanol, are higher than the parent ester MMA (i.e., a potential impact from Methanol can be excluded) so that adverse effects can be exclusively related to MAA.

 

Non-human data

MAA was tested in a study comparable to OECD 414 in groups of 19-25 pregnant female rats (whole-body inhalation exposure for 6 hr/day, during days 6 to 20 of gestation), at 0, 50, 100, 200, and 300 ppm (corresponding to 0, 179, 358, 716 and 1076 mg/m3 according to the OECD SIAR for short-chain alkyl-methacrylate esters, 2009; Saillenfait 1999). In dams, decreased body weight and feed consumption was observed at 300 ppm (1076 mg/m3), indicating a NOAEC for maternal toxicity of 200 ppm (716 mg/m3). No embryo- or foetal lethality, nor foetal bw effects or malformations after exposure with MAA was observed at any concentration. The NOAECs for fetetoxicity and developmental toxicity were considered 300 ppm (1076 mg/m3) MAA, respectively. This concentration corresponds to a body burden of 312 mg/kg bw/d considering physiological default parameters of ECHA guidance R.8 (2012; bw rat 250 g, respiratory turnover 0.29 m3/kg bw for 6 h of exposure) or, on molar level, 3.6 mM/kg bw/d.

The read-across substance MMA methacrylate was tested for its prenatal developmental toxicity in Himalayan rabbits according to OECD TG 414 (BASF 2010). MMA was administered as an aqueous preparation to 25 inseminated female Himalayan rabbits by stomach tube at doses of nominal 50, 150 and 450 mg/kg bw/d on gestation days (GD) 6 through GD 28. Slightly lower analytical values were reached (41, 132 and 406 mg/kg bw/d), likely to be a consequence of the high volatility of MMA and evaporation when handling the preparations.

At terminal sacrifice on GD 29, 24-25 females per group had implantation sites. In the mid and high dosed females, reduced food consumption (-13% and -18%, resp.) and body weight gain (-27% and -31%, resp.) was observed, while no test substance-related adverse effects were observed. In analogy to the aforementioned oral 2-gen study in rats, it is considered that these effects on food consumptions and bw gain were caused by  the pungent odour of MMA (odour threshold 0.5 – 1.5 ppm), rather than any substance-related systemic toxicity (cf. Borzelleca et al., 1964). In conclusion, the reduced food consumption and body weight gain are considered as treatment-related effects, which limited the applicable dose of the test compound. They are however not regarded as any true systemic toxicity because no accompanying clinical, clinical pathological and pathological signs were noted in previous and the present studies.

Thus the NOEL for maternal toxicity was considered to be nominal 50 mg/kg bw/d or actual 41 mg/kg bw/d, while the NOAEL for maternal toxicity was considered to be nominal 450 mg/kg bw/d or actual 406 mg/kg bw/d. Comparable to the MAA study in rats, no embryo- or foetal lethality, nor foetal malformations after exposure with MAA was observed at any concentration, leading to a NOAEL for foetotoxic and developmental effects of nominal 450 mg/kg bw/d or actual 406 mg/kg bw/d.

This actual dose is equivalent to a molar body burden of 4.1 mM substance/kg bw/d, which corresponds to 349 mg MAA/kg bw/d.

The impact of Methanol, as further primary metabolite, on the developmental toxicity hazard profile of MMA can be assessed with the help of an older teratogenicity study in rats (Nelson et al. 1985, as mentioned in the WHO EHC report #196, 1997). Here, Sprague-Dawley rats were exposed to either 6500 or 13 000 mg/m3 (5000, or 10 000 ppm) Methanol on GD 1-19 or 26 000 mg/m3 (20 000 ppm) methanol on GD 7-15 under a rather standard exposure regime (7h/d). A concentration of 6500 mg/m3 (5000 ppm) was found to be the NOAEC based on congenital malformations (predominantly extra or rudimentary cervical ribs and urinary or cardiovascular defects) at the next higher dose and in absence of maternal effects. This developmental NOAEC of Methanol corresponds to approx. 68 mMol/kg/d which indicates that Methanol does not contribute to potential effects of MMA when MMA is tested up to approx. 4 mMol/kg/d (as highest tested dose in the BASF study).

Justification for classification or non-classification

In the absence of signs of reproductive or developmental toxicity in a study and and by highly reliable read-across to its metabolic precursor MMA, MAA is not regarded as toxic to reproduction or as developmental toxicant.