Researchers To Examine Effects of MMT: Manganese: Essential Element, Yet Harmful in Gasoline?

The potential health effects of manganese particles released into ambient air from vehicles burning gasoline with the controversial octane-boosting additive MMT (manganese methylcyclopentadienyl) will be examined by a series of experiments to be conducted at the Chemical Industry Institute of Toxicology (CIIT) in Research Triangle Park, N.C. The testing is slated to begin next year and to run for at least four years. Photo courtesy of Ford Motor Co. WEAR AND TEAR: The two spark plugs show coloration differences between spark plugs from one car using MMT-containing gasoline (left) in Canada and another car not using MMT-containing gasoline in the United States, according to the Ford Motor Co. Inhalation experiments using monkeys and rats will examine the absorption, distribution, and elimination of what goes out the tailpipe when gasoline containing MMT is used in motor vehicles. The U.S. Environmental Protection Agency (EPA) and Ethyl Corp. of Richmond, Va., have been negotiating what specific tests are to be done and what will be investigated. Though there have been studies examining how much manganese is released into the air from cars burning MMT-containing fuel, the agency says more study is needed to determine the health impact of potential increases in the level of manganese in ambient air that result when MMT is burned on a large scale. A trace element, manganese is an essential part of the diet. It can easily be obtained from grains and nuts. Manganese deficiency can lead to bone problems and stunted growth. Excess dietary manganese is simply excreted. Manganese is also important industrially and is used to strengthen steel and aluminum. Manganese levels in the air vary widely; they are higher near foundries and metal plants and lower away from such facilities. A number of studies have shown occupational exposure to manganese can lead to Parkinson's disease-like symptoms, such as muscle tremors. But it's chronic exposure to manganese compounds coming from exhausts of vehicles fueled by gas with MMT that concerns some scientists. The CIIT tests occur against a contentious legal situation, which has pitted Ethyl Corp. at times against the EPA and the Canadian government over MMT. The MMT story in the United States began 20 years ago when Ethyl asked EPA for permission to add it to unleaded gasoline. EPA denied the request at first because of concerns that the additive would damage emission-control systems. Those concerns were allayed as a result of extensive and detailed tests of automobiles and trucks by Ethyl. Though EPA agreed MMT did not harm emissions systems, it sought to ban the additive due to concern about the potential health damage that might occur from widespread use of MMT; it lost in court. The court concluded EPA could not keep MMT out of gasoline on health grounds. Consequently MMT has been legal in the United States since 1995. Though Ethyl will not divulge numbers, the company says it is being used in gasoline today. Automakers remain concerned, however. Representatives of associations of U.S. and foreign vehicle manufacturer organizations assert that even at MMT levels used in American gasoline (1/32 gram per gallon), manganese may damage catalytic converters, which reduce hydrocarbon emissions; foul spark plugs; and interfere with the on-board diagnostic (OBD) system in today's cars. The manufacturers are conducting trials with MMT-containing gasoline to assess the specific impact on these systems. The results may be ready in 1999. MMT had been used for 20 years in gasoline in Canada. But in 1997 Parliament banned its import (none is made in Canada) due to environmental and health concerns, though Canada's health agency concluded in a 1994 report, "the combustion products of MMT in gasoline do not represent an added health risk to the Canadian population." That triggered a challenge by Ethyl under the North American Free Trade Agreement. In July the Canadian government backed off its ban, apparently concerned that it might lose and be forced to pay Ethyl a large sum of money in compensation for lost sales. Meanwhile, the EPA is requiring the CIIT testing under provisions of the Clean Air Act governing the health impact of fuel additives. While there have been studies of exposure to airborne particles of manganese, more study is needed to assess exposure and impact, according to Michael Davis, senior scientist in the Office of Research and Development of the National Center for Environmental Assessment of the EPA. Existing data, he says, is not sufficient. Based on one EPA-funded study in Riverside, Calif., in 1989 (E.G. Clayton et al., Journal of Exposure Analysis and Environmental Epidemiology, 3:227-50, 1993), EPA estimated that between 5 percent and 10 percent of the population might be exposed to manganese concentrations of 100 ng (nanograms) per cubic meter of air, says Davis. (When the testing was done, MMT was legal in leaded gasoline in California. It was banned from that fuel shortly thereafter.) The reference concentration is an estimate "of a continuous inhalation exposure level that is likely to be without appreciable risk of deleterious effects during a lifetime"(J.M. Davis, Environmental Health Perspectives Supplements, 106:191-201, 1998). An as-yet-unpublished study by Donna Mergler , professor of neurophysiology at the University of Quebec at Montreal, also funded by EPA, found that ambient exposure to manganese was tied to a range of problems. In people older than 50, greater exposure was linked to neuromotor problems as well as difficulties with learning and memory. In 1996, Mergler studied residents who lived near a smelter in southwest Quebec that used manganese and had closed five years previously. The ambient air concentrations of manganese were between 9 ng/cubic meter and 35 ng/cubic meter. These data are strictly preliminary, cautions Mergler. But Ethyl has sponsored research in metropolitan Toronto to examine manganese exposure that might be attributable to MMT use in gasoline. The 15-month study was conducted for Ethyl by Research Triangle Institute (RTI) between 1995 and 1996 (before the Canadian ban went into effect). RTI also conducted the Riverside study for EPA. The Toronto study (E.D. Pellizzari, accepted by Atmospheric Environment) found mean manganese exposures of 13.1 ng/cubic meter of air, far below the reference concentration. The study points out that manganese levels in subway stations were far higher--on the order of 150 ng/cubic meter. While that suggests manganese in air at subway stations may pose a greater health threat than manganese in ambient outside air, Mergler says the finding raises questions. "Where does the manganese come from? We simply do not know," she says. It could come from air intakes, making the subways a kind of manganese sink. Although the Toronto study finds low levels of manganese particles in the ambient air, Davis says it still leaves questions unanswered. "We have their report, and there are a lot of things we'll have to examine in it," says Davis in assessing its relevance to the United States. "There may be differences in meteorology, in traffic patterns, various things that make a difference in personal exposure levels," he says. "While Toronto might be comparable to a northeast city, I don't know if it will be comparable to a southwest city." Environmental Protection Agency3400 Highway 54Research Triangle Park, N.C. 27709Phone: (919) 541-4162 * Fax: (919) 541-0245E-mail:davis.jmichael@epamail.epa.gov www.access.gpo.gov/su_docs/aces/aaces002.html Davis also notes, "What they have done in Canada [the RTI Toronto study] is an exposure study, not a health-effects study. We don't really have a basis in terms of health effects information from Canada to judge this yet." Health effects might take 10 or 20 years to appear and might be very difficult to detect in an epidemiological study, he adds. A recent study using rats is also of concern to EPA. The research by Jorgen Henriksson and Hans Tjalve of the Swedish University of Agricultural Sciences finds that manganese particles can reach the brain via the olfactory nerve. "This way, manganese can circumvent the blood-brain barrier and gain direct access to the central nervous system," says Henriksson. The finding represents a new pathway for manganese to reach the brain, says Kenneth Hudnell, a neurotoxicologist at the National Health and Environmental Effects Research Laboratory of EPA. The study, which has been submitted to Toxicology and Applied Pharmacology, was presented at the 15th International Neurotoxicology Conference in Little Rock, Ark., in 1997. The conference focused on manganese. But Kenny Crump, a biostatistician and vice president of K.S. Crump Group Inc. in Ruston, La., sees no basis for worry about the health effects of manganese exposure as a result of MMT being burned in gasoline. "A reasonable look at the data is convincing to me there should not be concern," argues Crump, who was formerly on the EPA Science Advisory Board. Crump, who has consulted with Ethyl, has evaluated data on occupational exposure of factory workers to manganese. While he finds "subclinical effects" such as reaction time slowed by a few milliseconds, he finds no progression after more than a decade. And Donald Lynam, vice president for air conservation at Ethyl, dismisses EPA's concerns about manganese for MMT as misplaced: "We have long-term exposure to manganese regardless of whether there is MMT or not," he argues, saying manganese gets into the air anywhere there is a steel mill. "EPA says it's concerned about even lower exposures, which doesn't make sense." Though MMT is being used in gasoline in the United States, Canada, and other countries, it's clear that controversy around its possible health effects will remain lively for at least several years to come. Harvey Black, a freelance science writer in Madison, Wis., can be reached online at 73773.2227@compuserve.com.

Researchers To Examine Effects of MMT: Manganese: Essential Element, Yet Harmful in Gasoline?

Interested in reading more?

Become a Member of