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MPA Other Developments

Lower alkyl methacrylate esters are shown not to be of concern for cancer

Lower alkyl methacrylate esters1 are chemically-reactive molecules that are used to produce methacrylate-based plastics and resins. Their chemical reactivity (Michael reactivity) results in them combining with proteins such that they can be skin sensitizers in humans. This chemical reactivity also means that they can potentially react with other macromolecules such as DNA; raising the question of whether they might cause genetic damage; and therefore, be of concern for cancer. 

To investigate this question, MPA sponsored Dr. Richard Albertini, an independent and eminent genotoxicity expert at the University of Vermont, to review the extensive studies on the lower alkyl methacrylates and publish his findings in a peer-reviewed journal. Dr. Albertini found that in studies in bacteria, which are often used to identify chemicals that might cause cancer in humans, the lower alkyl methacrylates did not cause permanent alterations in DNA. In tests using animal cells in glassware (in vitro) with very high concentrations of the methacrylates, there was disruption or breakages of chromosomes, but Dr. Albertini concluded there was no convincing evidence that the lower alkyl methacrylates cause this type of damage in live animals. This is consistent with the lack of carcinogenicity of methyl methacrylate observed in studies of both animals and humans. Dr. Albertini explained the observation in glassware as likely being due to the high concentrations and to generation of metabolites under these artificial conditions – metabolites that do not occur in animals and humans when exposed to these chemicals. Overall, Dr. Albertini concluded that lower alkyl methacrylate esters are not of concern for cancer.

1The lower alkyl methacrylates are methyl methacrylate (MMA), the largest volume monomer, as well as ethyl methacrylate (EMA), hydroxyethyl methacrylate (HEMA), n-, i- and t-butyl methacrylate (BMA) and 2 ethyl hexyl methacrylate (2-EHMA), as well as methacrylic acid (MAA).

Statement Regarding AOEC Classification of Methyl Methacrylate

In its online Exposure Code database, the Association of Occupational and Environmental Clinics (AOEC) codes methyl methacrylate (MMA) as an asthmagen and respiratory sensitizer.  A number of thorough and careful evaluations of MMA have concluded it cannot be classified as an asthmagen or respiratory sensitizer.

The AOEC exposure codes, which were assigned by a single reviewer, do not comport with the findings of other scientific bodies. The Methacrylate Producers Association believes that the science does not support a finding that MMA is an asthmagen or a respiratory sensitizer.  For more information, see MPA's position paper.

Department of Transportation and Congress Set New Rail Transportation Rules Applicable to Methyl Methacrylate

With a final rulemaking by the Department of Transportation (DOT) in May 2015, which was modified by a subsequent Act of Congress in December 2015, the Department and Congress set new safety rules for rail transportation of flammable liquids. Although primarily targeting crude oil and ethanol shipments, the rule applies to shipment of all Class 3 flammable liquids and thus to methyl methacrylate (MMA). MPA had commented on the Department’s proposed rules, expressing concern about the need for such rules given the methacrylate industry’s voluntary adoption of higher-safety tank cars, as well as the foreshortened and likely unrealistic timeline proposed for implementing required retrofits (or obtaining new tank cars built to the new DOT-117 specifications). DOT’s final rule was not adequately responsive to such concerns. Congress stepped in with provisions in the” Fixing America’s Surface Transportation Act” (FAST Act) which modified the DOT rule. For Packing Group II substances such as MMA, improved tank cars must be used for transport after May 1, 2029, consistent with MPA’s comments requesting an extended period for implementation of the new rules. DOT can extend this deadline by two years if it determines there is insufficient shop capacity to meet the 2029 deadline. Further, in lieu of meeting the full DOT-117 standards, retrofitted tanks cars may comply with DOT-117R standards, which many tanks cars in MMA service already meet. The voluntary adoption of tank car enhancements by MMA members has contributed to an outstanding safety record for rail transportation of MMA.

ACGIH® Recommended TLVs for Methyl Methacrylate

In response to recent announcements by American Conference of Governmental Industrial Hygienists (ACGIH), MPA comments to ACGIH supporting the recommended Threshold Limit Values (TLVs) for Methyl Methacrylate (MMA).  These limits are consistent with occupational exposure limits set by the European Union SCOEL (Scientific Committee on Occupational Exposure Limits).  However, two statements concerning potential respiratory and skin sensitization have been included that are not supported by a wider evaluation of the literature, and could lead to misunderstanding by ACGIH’s intended audiences.

Health Review on Asthma

The health effects of MMA are well understood. MMA liquid is recognized as being irritating to the eyes and is a weak skin-sensitizer that may cause skin allergy (allergic contact dermatitis) following skin contact. High concentrations of the vapor are also irritating to the respiratory system. As irritant vapors (cold air, smoke etc.) may worsen the symptoms in individuals that have sensitive airways, such as asthmatics it is not surprising that there has been much debate and confusion about whether or not MMA exposure can also cause respiratory sensitization (occupational asthma).  Dr. Jonathan Borak, MD, DABT (Departments of Epidemiology and Public Health and Medicine, Yale University) conducted a critical review all the available information and the results are included in a publication in Critical Reviews in Toxicology in which he concludes that the "weight of evidence" supports the conclusion that "MMA is not a respiratory sensitizer". For for information, see Methacrylates and Asthma.

REACH

REACH is the European Union (EU) regulation for Registration, Evaluation, Authorisation and Restriction of Chemicals. It entered into force on 1st June 2007 with the objective to protect human health and the environment from the risks that can be posed by chemicals.

The Methacrylates REACH Task Force, comprised of MPA’s member companies along with other manufacturers in the EU and Japan, successfully completed the registration of the lower methacrylates (MAA, MMA, EMA, nBMA, iBMA and 2-EHMA) as a group of related esters (or category) in October 2010, before the December 1st deadline for high production volume chemicals (>1000 tpa). The registrations included the conduct of several studies to meet data requirements for compounds in the highest tonnage band, a comprehensive hazard assessment for each compound, as well as an assessment of safe handling conditions for identified uses of each compound.

Assessment of the Skin Sensitizing Potency of the Lower Alkyl Methacrylate Esters

A 2014 publication in Regulatory Toxicology and Pharmacology, "Assessment of the skin sensitising potency of the lower alkyl methacrylate esters" reports that Methyl Methacrylate and other lower alkyl methacrylates had weak skin sensitizing potency.

Methacrylate Polymers Do Not Cause Skin Sensitization When Handled

A 2014 publication in Regulatory Toxicology and Pharmacology, "Risk Assessment of residual monomer migrating from acrylic polymers and causing allergic contact dermatitis during normal handling and use" reports that methacrylate polymers do not cause skin sensitization when handled.

For more information, see MPA Archived Developments.