Formaldehyde, oligomeric reaction products with aniline

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DMEL (Derived Minimum Effect Level)

Value:

0.014 mg/m³

Most sensitive endpoint:

carcinogenicity

DNEL related information

Overall assessment factor (AF):

3 125

Modified dose descriptor starting point:

T25

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DMEL (Derived Minimum Effect Level)

Value:

0.004 mg/kg bw/day

Most sensitive endpoint:

carcinogenicity

DNEL related information

Overall assessment factor (AF):

12 500

Modified dose descriptor starting point:

T25

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

high hazard (no threshold derived)

Additional information - workers

 

Justification on read-across of data for the 4,4´-isomer of MDA for oligomeric MDA in the scope of REACH.

Oligomeric MDA (oMDA) is produced by a condensation reaction between aniline and formaldehyde. The main component of the crude product is 4,4’-MDA, which makes up 46 to 65%. Further, the crude product contains minor amounts of methylene-2,4’-dianiline and traces of methylene-2,2’-dianiline. The other main component is a mixture of higher oligomers.

The general molecular formula is:

 H₂N-C₆H₄-[H₂N-C₆H₄]_m-C₆H₄-NH₂

The higher oligomers include mainly 3-ring (m=1; product of 3 aniline + 2 formaldehyde) together with other higher number ring types (m=4-7; 4 to 7 aniline with 3-6 formaldehyde) as shown in the table below.

Following nomenclature for the isoformes are defined:

 

1) CAS name: Benzenamine, 4,4'-methylenebis- (mono constituent substance), CAS number: 101-77-9. EC name: 4,4'-methylenedianiline, EC number:202-974-4

2) CAS name: Formaldehyde, polymer with benzenamine (UVCB), CAS number 25214-70-4. EC name: Formaldehyde, oligomeric reaction products with aniline, EC number: 500-036-1.

Concentration ranges of MDA-isoforms [%]:

CONTENT	4,4’-MDA	Oligomeric MDA
4,4’-MDA	75-100	46-65
2,4’-MDA	0-20	0.8-1.4
2,2’-MDA	0-5	<0.1
Formaldehyde, oligomeric reaction products with aniline	0-15	3- to 7-ring isomers concentrations shown below
3-ring isomers	No data	22-28
4-ring isomers	No data	12-14
5-ring isomers	No data	6-8
6-ring isomers	No data	3-5
7-ring isomers	No data	1-3

2,4'-methylenedianiline: CAS number 1208-52-2, EC number 214-900-8

2,2'-methylenedianiline: CAS number 6582-52-1, EC number 229-512-4

 

Comparison of physico-chemical properties of MDA-isoforms:

Property	4,4’-MDA	oligomeric MDA
Melting range	83 - 92°C	30 - 70°C
MW [g/mol]	198.26	233 (average)
water solubility [g/l]	1.01 (at 25°C)	0.36-1.22 (at 20°C)
logPow(at 25°C)	1.55	1.3 - 2.5
Vapor pressure [hPa]	0.00025 Pa at 25°C	<0.000001hPa at 20°C

 

Since 4,4’-MDA is the main constituent of both isoforms, toxicological properties of the incompletely tested oMDA can be extrapolated from this isomer by means of a worst case consideration. All isomers and homologues have primary aromatic amino groups as a common property.

The leading health effects of 4,4’-MDA are liver toxicity, carcinogenicity and sensitization. These effects may, at least partly, be driven by the bifunctional diamine-structure of the 2-ring molecule in 4,4´-position. In higher-ring compounds it may be predicted that this functionality, at least partly and to an alleviated extent, still exists.

Taking into account the higher degree of saturation of functional groups and the altered physico-chemical properties (higher molecular weight, decreased vapour pressure, decreased water solubility, unchanged / decreased logP_owat physiological pH) a lower reactivity and bioavailability of oMDA can be anticipated.

As a proof of concept data from dated industrial hygiene studies and a chronic study in rats can be used:

·   acute i. p. toxicity in mice demonstrated lower toxicity for oMDA (LD₅₀0,5 g/kg bw, BASF AG 1973) than for 4,4’-MDA (LD₅₀0.147 g/kg bw, BASF AG 1965).

·   acute oral toxicity in rats demonstrated lower toxicity for oMDA (LD₅₀0,7 g/kg bw, BASF AG 1973) than for 4,4’-MDA (LD₅₀0.444 g/kg bw, BASF AG 1975).

·   both isoforms are non irritating on skin and mucosa.

·   subcutaneous injections of 3- and 4- ring fractions of MDA into rats resulted in a significantly lower acute toxicity (LD₅₀2.5 g/kg bw) than 4,4’-MDA (LD₅₀0.2 g/kg bw, Bayer AG 1969). In the same study chronic subcutaneous injections of 3- and 4-ring fractions of MDA were better tolerated than 4,4’-MDA. Life expectancy and tumour incidence of animals injected with a high total dose of 11.2 g/kg of 3- and 4-ring fractions of MDA was approximately identical to the animals injected with a lower total dose of 1.41 g/kg 4,4’-MDA. This trend of decreasing systemic toxicity with increasing number of aromatic rings in the amine molecule was supported by chronic subcutaneous injections of a 8-ring fraction of MDA.

Even though the quality of the cited studies does not comply with current guideline requirements, these considerations support the proposal that 4,4’-MDA can be taken as a reference molecule for oMDA. The data available on 4,4’-MDA can therefore be considered representative for the category for the purpose of hazard evaluation and risk assessment.

 

Accordingly, the classification of oMDA can be adapted from 4,4’-MDA by means of a worst case consideration:

                       

GHS:  

carc. cat. 1B

muta. cat. 2

STOT single exp. cat 1

STOT rep. exp. cat 2

skin sens. cat.1

In order to support the legal classification key studies of 4,4’-MDA for all relevant end point were included into the oMDA IUCLID.

 

 

Rational for choice of toxicological key values:

The main target organs of MDA’s carcinogenic and non-carcinogenic effects in rodents are the liver and the thyroid gland. Also in humans liver effects following MDA exposure were documented. Moreover MDA is a skin sensitizer in humans.

 

Dermal Absorption:

Following dermal application (2 mg/kg bw onto 2cm² application area) MDA was well absorbed in rats (50% in 96h), though to a minor extent in guinea pigs (29% in 96h) and monkeys (21% in 168h) (El-Hawari et al., 1986). The transport process exhibited saturable transport kinetics and significant amounts of MDA were recovered in the skin of the application area at the end of the observation periods. In an occlusive in vitro dermal penetration assay resorption rates of 33% were determined with isolated human skin and 13% with isolated rat skin during an observation period of 72h (Hotchkiss et al., 1993). These resorption rates decreased significantly when the application area was not occluded. Similar to the in vivo assay major amounts of radioactivity were recovered in the skin surface.

 

Acute toxicity:

Following single oral ingestion MDA exhibits severe irreversible liver toxicity with adistinct interspecies differencein severity.

In rats gross pathological liver and eye effects were noticeable from dose levels of 400 mg/kg bw (BASF AG, 1961, 1965). Microscopically, hepatocellular necrosis was observed in male rats treated with 100 mg/kg bw MDA and markers of liver injury (e.g. serum bilirubin, liver weight) were already altered at dose level as low as 25-75 mg/kg bw. These observations were supported by Dugas et al. (2001) demonstrating that a single oral dose of 25 mg/kg (female rat) or 50 mg/kg bw (male rat) resulted in bile duct injury and an increase in AP, GGT, ALT and bilirubin in serum.

As expected for an aromatic diamine cats were shown to be the most susceptible species for systemic MDA liver toxicity, followed by dogs, rats and rabbits (Oettel and Hofmann, 1961).In an acute gavage study performed with cats (Oettel & Hoffmann, 1961), animals at the lowest dose of 10 mg/kg were without clinical signs, though hematological, renal and hepatic disturbances were observed.Significant macroscopic liver effects (icterus) were observed with 25 mg/kg bw and higher dose levels additionally affected the kidneys and the eyes. Severe, irreversible mydriasis, followed by blindness was observed in almost all cats from dose levels of 25 mg/kg bw. Similar effects on the eyes were observed in dogs (from 100 mg/kg bw) and rabbits (at 300 mg/kg bw).

 

Repeated dose toxicity:

Subchronic uptake of MDA by rats via the drinking water resulted in irreversible hemotoxic effects, irreversible hyperplasia of small biliary ducts and stimulation of the follicular epithelium in the thyroids (Ciba-Geigy, 1982).The LOEL was identified as 7.5 mg/kg bw. With respect to organ toxicity female animals were more susceptible than males and rats were more susceptible than mice.

 

Carcinogenicity.

The point of departure for the DMEL derivation were liver tumors in rats observed in a chronic drinking water study with MDA hydrochloride (NTP, 1983). This tumor type was identified as the most critical regarding incidence and dose levels. Oral uptake of 9 mg/kg bw resulted in a significant increase in neoplastic liver nodules (LOAEL 9 mg/kg bw) withmale rats being more susceptible than female rats and rats generally being more susceptible than mice.Additionally one carcinoma was observed in each male dose group. The thyroid tumors in rats and the liver tumors in mice cannot be conclusively evaluated with respect to their human relevance.

No data is available to evaluate carcinogenicity on the inhalation route of exposure and only a chronic study of very low reliabilitiy is available for the dermal route of exposure. However this study confirmed the liver as primary target of liver neoplasms.

The mechanism of carcinogenicity is not yet fully understood. Genotoxic and/or secondary mechanisms (e.g. thyroid stimulation following glucuronidation in the liver) can be postulated. Based on this uncertainty, a DMEL needs to be derived for the safety assessment based on the conservative assumption of a genotoxic mechanism of liver carcinogenesis.

 

Toxicity to reproduction:

The reliability of the little data available for reproductive toxicology of MDA is low and does not allow the derivation of a reliable dose descriptor. However, the hazard and safety assessment of MDA with respect to reproductive toxicology is superimposed by its classification as a Cat 2 carcinogen.

 

Details:

The following DNELs / DMELs were not derived:

• oral exposure:In principle ingestion is not an anticipated route of exposure in an industrial setting,since general workplace hygiene prevents any oral ingestion. Particularly for MDA as Cat 2 carcinogen the low occupational exposure limits applied also prevents any oral ingestion at the workplace.

• acute effects: occupational exposure limits for carcinogens (DMEL for MDA, Cat 2 carcinogen) are established as 8 h time weighed averages, a ceiling factor for acute peak exposures is not envisioned. Acute occupational exposure limits are designed to prevent local irritation for example (not relevant for MDA, see above) or adverse systemic effects. In the case of MDA the derivation of a DNEL for acute-systemic-effects would result in a significantly higher value and would therefore be misleading with respect to the derived DMEL.

Acute/short-term exposure – systemic effects – dermal DNEL

Not quantifiable; see above

 

Acute/short-term exposure – systemic effects – inhalation DNEL

Not quantifiable; see above

 

Acute/short-term exposure – local effects – dermal DNEL

Not quantifiable; see above

 

Acute/short-term exposure – local effects – inhalation DNEL

Not quantifiable; see above

 

Long-term exposure – systemic effects – dermal DNEL

Neoplastic liver nodules in a chronic drinking water study in male rats were identified as the most critical systemic effect (see explanation above).A linear increase in the dose range tested was observed, resulting in aLOAEL of 9 mg/kg bw at which 13 out of 50 male rats were affected (12 nodules, 1 carcinoma), compared to 1 out of 50 in the control group.

 

Adaptation of starting point:

Net incidence at 9 mg/kg/d = (13-1)/50 = 0.24 = 24 %

T25_{oral, rat}= 9 mg/kg bw * 25%/24% = 9.375 mg/kg bw

 

Route to route extrapolation:   

Basic assumptions:     100% bioavailability oral

50% bioavailability dermally in rats (El-Hawari et al, 1986).

T25_{dermal, rat}= 9.375 mg/kg bw / 0.5 = 18.75 mg/kg bw

 

“Large assessment factor approach” for the derivation of a DMEL (see ECHA guidance chapter R8, appendix R.8-7):

following factors were:

• Allometric scaling rat → man: 4


• remaining differences: 2.5 (covering e.g. differences in toxicodynamics)


• intra-species differences: 5 (for workers)


• point of comparison: 10 (not having a NOEL)


• nature of carcinogenic process: 10 (genotoxic carcinogen)


• T25 instead of BMDL10: 2.5

Adaptation for differences in worker and experimental exposure conditions:

Workers exposure is 5 days a week, 48 weeks a year and 40 years in an average lifetime of 75.

This results in a correction factor of 2.8(7/5 days/week * 52/48 weeks/year * 75/40 years/life). 

 

DMELdermal, worker = 18.75 mg/kg bw / 12500 *2.8 = 4.2 µg/kg bw

 

Due to the conservative nature of the DMEL derivation, systemic organ toxicity is sufficiently covered by the DMEL (DNEL derivation not presented).

 

Long-term exposure – systemic effects – inhalation DNEL

T25_{oral, rat}= 9.375 mg/kg bw (seelong-term exposure – systemic effects – dermal DNEL for explanation).

 

Route to route extrapolation:   

The bioavailability of MDA after oral application is at least 90 % (see explanation) and therefore as a conservative approach similar bioavailabilities for the oral and inhalation route of exposure need to be anticipated.

 

T25_{inhal., human}=   T25_{oral, rat}* (1/sRV_rat) * (ABS_{oral rat}/ABS_{human inhal.}) * (sRV_human/RV_worker)

T25_{inhal., human}=   9.375 mg/kg bw* (1/0.38 m³/d) 100%/100% * (6.7/10) = 16.5 mg/m³.

 (sRV:                       standard respiratory volume (for rat 0.38 m³/kg/8h or 1.15 m³/kg/24h))

 

“Large assessment factor approach” for the derivation of a DMEL (see ECHA guidance chapter R8, appendix R.8-7):

following factors were applied:

•  Allometric scaling rat → man: 1 (allometric scaling does not need to be applied in cases where doses in experimental animal studies are expressed as concentrations (mg/m3)).


• remaining differences: 2.5 (covering e.g. differences in toxicodynamics)


• intra-species differences: 5 (for workers)


• point of comparison:  10 (not having a NOEL)


• nature of carcinogenic process:  10 (genotoxic carcinogen)


• T25 instead of BMDL10:  2.5

Adaptation for differences in worker and experimental exposure conditions:

Workers exposure is 5 days a week, 48 weeks a year and 40 years in an average lifetime of 75. This results in a correction factor of 2.8(7/5 days/week * 52/48 weeks/year * 75/40 years/life).

 

DMELinhal., worker = 16.5 mg/m3 / 3125 *2.8 = 14.8 µg/m3

 

Due to the conservative nature of the DMEL derivation, systemic organ toxicity is sufficiently covered by the DMEL (DNEL derivation not presented).

 

Taking into account an acceptable risk of 4:100000the Committee for Hazardous Substances of the German Authority for Occupational Safety and Occupational Medicine (BAuA) derived an exposure risk value for4,4’-Methylendianiline equivalent to 7.3 µg/m3. This value is in the same order of magnitude as the value derived above, though the derivation parameter was not as refined.

 

Long-term exposure – local effects – dermal DNEL

Not quantifiable; see above

 

Long-term exposure – local effects – inhalation DNEL

Not quantifiable; see above

 

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

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:

no hazard identified

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

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Most sensitive endpoint:

repeated dose toxicity

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

no hazard identified

Additional information - General Population

Consumer DN(M)EL

It is possible to calculate consumer DN(M)EL long term, (dermal and inhalation route-systemic), by increasing the assessment factor for intra-species differences from 5 to 10. Though, since no exposure of the general population is likely because the product is only used in fixing radioactive material and is bound in a matrix. Consumers are not intended to use the substance.  Radioactive waste is stored in the way which prevents exposure of consumers to the substance or any environmental contamination.