Methyl Tertiary-butyl Ether

This report evaluates the risks to human health and to the environment posed by exposure to methyl tertiary-butyl ether (MTBE), which is used almost exclusively as a fuel additive.

A summary of sources of human and environmental exposure is followed by an assessment of the chemical's environmental behaviour and fate.

Studies demonstrate that, after discharge into air, MTBE largely remains in the air, with smaller amounts entering soil and water.

Although atmospheric MTBE can partition into rain, data indicates that atmospheric transformation by hydroxyl radicals is a more important pathway of removal.

Concerning environmental levels and human exposure, evaporative emissions from oxygenated gasoline are identified as the main source of exposure for the general population.

Widespread exposure via inhalation is noted to occur during time spent at service stations, while driving cars, in public parking garages, and in homes with attached garages. The report also cites data on exposure levels obtained in numerous studies of urban air, in facilities where MTBE is manufactured or blended, and in such occupational settings as service stations and garages, and in the transportation of neat MTBE and fuel mixtures through pipelines, barges, railroad cars and trucks.

There follws a review of the kinetics and metabolism of MTBE, drawing on toxicokinetic data derived from controlled studies of healthy adult volunteers and in occupationally-exposed workers.

Data indicates that MTBE is rapidly absorbed into the circulation following inhalation.

From studies in laboratory animlas, the report identifies the principal signs of intoxication as depression of the central nervous system, ataxia and laboured respiration.

It found no evidence of adverse effects on reproduction, genotoxicity and mutagenicity.

Inconclusive findings on carcinogenic studies were noted.

An evaluation of health effects in humans reveals that, shortly after the introduction of MTBE-blended gasoline in the USA. there were health complaints involving headache, eye and nose irritation, cough, nausea, dizziness and disorientation. The report also draws on findings from epidemiological studies of occupationally-exposed workers and experimental studies of volunteers exposed in inhalation chambers.

It concludes that MTBE alone, under common conditions of inhalation exposure, is not likely to induce adverse health effects in the general population.