Exposure to Methacrylates

General Overview

There are no known major natural sources of methacrylate esters. Exposure to the monomers in the concentrated state occurs primarily in the workplace. Because these are reactive materials they are handled under strictly controlled conditions when they are manufactured and processed. Workers are trained and provided with the equipment needed to control exposure. In manufacturing/processing, chemical industry operators are responsible for the production of the esters or polymers, while downstream processors make the dispersions or other compounded or fabricated items.

Regarding exposure, the end products produced from these monomers fall into two categories, those used by professional applicators and those that are meant for the consumer market.

The materials intended for the professional applicators can include uncured resins that are used as adhesives or finish coatings, glues or fillers to repair plastic articles, some health care products such as dental appliances or fillings. Professionals who use these materials are provided with the information on how to use them safely. The amounts of monomer in medical products are regulated. The final products produced or repaired with these materials contain very low levels of unreacted monomer.

Consumer exposure to monomers from finished products made with the polymers is very low and both oral and dermal exposures are considered to be negligible. The vast majority of products available to consumers are made from cured resins. Examples include: coatings or surface finishes, glass substitutes, molded fixtures or appliance parts, toys, packaging, sporting equipment, etc. In some products like glues or cements, varnishes or other finishes, consumers may be exposed to residual monomers until the adhesive or coating dries. For these materials, the package labels give instructions on safe use. These instructions include use in a well ventilated area and preventing contact with the skin. Use in artificial nail products and other non-medical/dental applications involving direct skin/nail contact with the liquid monomer is not recommended or supported by the MPA member manufacturers. In summary, consumer exposure to liquid monomer is unlikely unless they intentionally use professional/DIY or hobbyist products that contain significant levels of liquid monomer. Consumer exposure is primarily only to the extremely low levels of residual monomer in fabricated consumer products.

Technical Overview

There are no known major natural sources of methacrylate esters. To understand the possibilities for exposure it is important to understand the scope of the associated applications and products. In manufacturing/processing, chemical industry operators are responsible for the production of the esters or polymers, while downstream processors make the dispersions or other compounded or fabricated items. In professional/ commercial settings, applicators or technicians who may come into contact with the ester monomers or polymers include dental technicians, trained manicurists, paint and coating applicators, mechanics and auto repair technicians. Consumers could be the recipients of articles applied by professionals, like the dental appliances, artificial nails, etc, or could be the users of the products like latex paints, adhesives, or fabricated items.

Occupational exposure to short chain alkyl methacrylates is most likely to occur through inhalation and dermal contact during the production, transportation, or use of these compounds. The occupational exposures limits (OEL) that have been defined for methyl methacrylate, are generally in the range of 50 - 100 ppm as a time weighted average for an 8 hour workshift; OELs for ethyl methacrylate are generally in the range of 25 - 100 ppm; for the butyl methacrylate isomers they are generally in the range of 25 - 50 ppm. No OELs have been set for 2-ethylhexyl methacrylate. All of these materials are considered skin sensitizers.

Among the professional trades, trained manicurists use small quantities of EMA in the application of artificial acrylic fingernails. Artificial fingernail and nail-repair kits are also sold to the general public. In this application there is potential for inhalation exposure and for direct contact between liquid monomer and the nail, and sometimes the skin.

Small quantities of methacrylate esters are also used in the manufacture and repair of dental prosthetics by trained technicians. Polymeric dental products (dentures and denture prosthetic devices) will contain low levels (typically below 1%; ISO Standard 1567 specifies less than 2.2% for dentures) of total methacrylate monomers; hence consumer exposure to low levels of migrant monomers, via the oral mucosa, may occur.

Consumer exposure to methacrylate monomers, by skin contact with PMMA, or oral intake from use of PMMA articles, is regarded to be negligible. End-use consumer products contain low levels of methacrylic acid esters (as a result of polymerization) and their rate of migration from acrylic polymers is low.

As an example, exposure to BMA (isomer not specified) during use of methacrylate polymer based toners in facsimile machines has been reported as 0.045 ppm (0.21 mg/m3) (Fannick (NIOSH), 1981) and between 0.02 and 0.1ppm (0.14 and 0.6 mg/m3) (Raymond, 1996).

The Methacrylate Producers Association in the US and the Methacrylates Sector Group of the European Chemical Industry Council published a "Methacrylate Esters Safe Handling Manual" in 2002 for use by their customers. The manual provides information on characteristics, potential health effects, industrial hygiene, reactivity, shipping, storage handling and disposal, applicable to typical use scenarios.