The Health Effects Institute
"A Partnership of the U.S. Environmental Protection Agency and Industry"

ATTACHMENT A:
SUMMARY OF A WORKSHOP ON METAL-BASED FUEL ADDITIVES AND NEW ENGINE TECHNOLOGIES

Introduction
Overview of Metal Toxicity
Control of Vehicle Emissions
The Case of MMT
Application Process and Deadlines

INTRODUCTION

Metals comprise a large and diverse group of elements with a broad range of toxic effects. While certain metals are highly toxic in all forms, others, within narrow concentration ranges, are essential to living systems. However, even these essential metals can be toxic at higher concentrations. Metals are not biodegradable, but can be transformed into different chemical forms, often with different valance states. Some of the transformation processes result from activities related to industrialization, including combustion of fuels, or other temperature-driven reactions associated with motor vehicle performance. Metals are being emitted into the environment in increasing amounts, and sometimes in forms with differing toxicity. Metals may also be part of particulate matter, and are hypothesized to contribute to their toxic effects.

Metals are used in a variety of ways in motor vehicles, including:

Although the intention of metal use is beneficial, such as to reduce emissions of concern, metals have the potential of causing deleterious effects themselves or of causing other changes in emissions that may increase toxicity (such as changing the particle size distribution). Therefore it is important to be informed about the potential health effects of new metal-containing fuel additives or engine developments before their widespread adoption. Because it is difficult to predict the toxicity of one metal based on effects of another, and because the chemical form of the metal may affect its toxicity, it is critical to conduct research on new metal additives before their widespread use. Because of the cost of conducting such research, it is important to understand how likely the use of different metals will be in order to focus the research appropriately.

To become better informed about potential uses of metals and their toxicity, HEI brought together representatives from government, industry, and academia with expertise in engine technology and toxicology to share their perspectives about new developments and research needs at a workshop on February 4, 1998. The workshop began with a comprehensive presentation on metal toxicity and then focused on two general areas: vehicle emissions and their control, including metal additives that may have the effect of controlling some types of emissions (ferrocene and cerium-containing catalysts), and methylcyclopentadienyl manganese tricarbonyl (MMT), an additive that may be used in gasoline as an anti-knock agent. The following summary of the workshop proceedings is intended to provide a brief overview of the presentations and perspectives brought by participants.

Opening the discussion, Dr. Robert Sawyer (University of California, Berkeley, and HEI Research Committee) noted that a number of metals are presently found in motor vehicle emissions and several metal additives are under consideration for future use. Currently proposed metal additives are used or would be used at relatively low levels compared to lead, which was used in concentrations of parts per 1000 starting in the late 1920s. However, since the toxicity of different compounds varies greatly, it is important to understand the toxicity of emissions from metal-containing fuels before their use becomes widespread. Dr. Sawyer stated that the goal of the workshop was to help HEI define priorities for a research program on metals by understanding better what additives are most likely to be used, how much is known about their chemical form and concentration in emissions, the toxicity of these emissions, and what research is being conducted.

OVERVIEW OF METAL TOXICITY

Dr. Michael Waalkes, National Cancer Institute at NIEHS, provided an overview about properties of metals and their toxicity. Metals are a broad class of elements comprising about 80% of the periodic table. They are widely distributed in the environment and are not biodegradable. Common physical properties of metals include electrical conductivity and thermal conductivity, and they can be deformed without cleaving under stress. Metals have a tendency to donate electrons and to form basic oxides. Many exist in a number of different valence states and form a vast variety of inorganic and organic compounds. Biologically, many metals are essential to living systems and are involved in a variety of cellular, physiological, and structural functions. They often are cofactors of enzymes, and play a role in transcriptional control, muscle contraction, nerve transmission, blood clotting, and oxygen transport and delivery. Although all metals are potentially toxic at some level, some are highly toxic at relatively low levels. Moreover, in some cases the same metal can be essential at low levels and toxic at higher levels, or it may be toxic via one route of entry but not another. Toxic effects of some metals are associated with disruption of functions of essential metals. Metals may have a range of effects, including cancer, neurotoxicity, immunotoxicity, cardiotoxicity, reproductive toxicity, teratogenicity, and genotoxicity. Biological half lives of metals vary greatly, from hours to years. For example, nickel has a half life of 30 hours in the human body, methyl mercury 70 days, and cadmium 20 years. Furthermore, the half life of a given metal varies in different tissues. Lead has a half life of 14 days in soft tissues and 20 years in bone.

In considering how to evaluate the toxicity of metals of potential concern, a number of aspects of metal toxicity should be kept in mind:

CONTROL OF VEHICLE EMISSIONS

Reducing vehicle emissions is a critical and continually developing process. In this section of the workshop, presenters discussed current and future approaches that manufacturers of automobiles and engines are taking to reduce emissions. They also discussed what kinds of research on emissions and toxicity has been done on metal additives that are in use or are currently under consideration .

Diesel Engine Technologies Using Metal Fuel Additives

Dr. Robert Hammerle (Ford Motor Company) discussed some of the factors that are leading auto makers to explore new technologies and emission control techniques including those that use metals; for example the pressure to limit CO2 emissions because they are thought to contribute to global warming. He pointed out that diesel engines are desirable from that perspective because, for a given amount of work, emissions of CO2 are about 20% lower from diesel engines than from gasoline engines. However, diesel engines emit much higher levels of particles than gasoline engines, raising concerns about potential health effects of particles.

One way to control diesel particulate emissions is to use after-treatment devices. Filters (or traps) can remove up to 98% of particulate mass from exhaust gas. However, because the particles fill and plug the filter, periodic burning (regeneration) is necessary. Fuel additives used in conjunction with the traps generate fine metal oxide particles that lower the soot ignition temperature. Oxides of several kinds of metals are effective; these include lithium (at 5 ppm), sodium (at 15 ppm), iron (at 40 ppm), and cerium (at 100 ppm). About 1% of the metal consumed may be emitted in the tailpipe exhaust. This translates to emission of 1.7 mg per mile of oxides of lithium at 40 mpg, 3.9 mg for sodium, 9.1 mg for iron, and 19.6 mg for cerium.

Two alternative methods of initiating particle regeneration of filters do not require using fuel additives, but do have some drawbacks. These methods are: 1) Auxiliary heaters that raise exhaust to 550° C; these require a great deal of equipment; 2) exhaust catalysts that lower soot ignition temperature but generate NO2 and work only with fuel containing less than 50 ppm sulfur.

Several filter designs have been used effectively for more than 100,000 miles on city buses. They are more difficult to adapt to cars because automobile exhaust temperatures are lower, space for the filters is more limited, and maintenance less frequent. Filters have not yet been used on production cars, but will probably be used on future diesel cars in order to comply with particulate emission standards. One of the simplest particulate filters will use metal additives such as cerium to help regeneration; however, before they are introduced it is important to understand the health effects of the additives.

Technological Approaches to Reducing Emissions

Mr. Robert Jorgensen (Cummins Engine Company) discussed design changes to meet current standards for particulate and NOx emissions from heavy-duty diesel engines. Relative to 1970 standards, 1998 standards for diesel emissions require a 73% decrease in NOx and a 90% decrease in PM; proposed standards for 2004 are the same for PM but require an additional reduction in NOx emissions (to a total reduction of 87% relative to the 1970 standards). Because technological changes to address one of these pollutants may affect the emission level of the other, maintenance of low level emissions of both is a challenge. Cummins does not foresee a need for fuel additives to meet the proposed 2004 standards; beyond 2004 that may be necessary. Cummins prefers changes in the engine to decrease emissions to after-treatment devices because they are more reliable and cannot be tampered with.

In the past, a variety of design changes have enabled Cummins to meet standards. Design changes are different for different sizes of engines. To meet the 1998 standards, important changes in heavy-duty diesel engines involved air handling, fuel handling, and the combustion system (further retardation of injection timing). For medium heavy-duty diesel engines, important developments were full authority electronic fuel injection systems with injection rate control, centralized piston bowl and injector location, and four valve heads.

Looking toward the 2004 standards, further technical advances will be needed. These may include:

air handling system: exhaust gas recirculation, variable geometry turbo charging

fuel handling system: increased injection pressure

The use of filters involves a number of technical hurdles. These hurdles include deposit buildup and plugging of the trap as a result of such causes as cold ambient temperatures, sustained low-load operation, and potential suspension of additive use. From an environmental perspective, problems include removal of the system or tampering with the system to avoid operational costs, to obtain performance improvement, or because of suspended use of the additive.

Evaluation of Engine Exhaust Derived from Fuel Containing Ferrocene

Ferrocene is a coordination compound of iron and two molecules of cyclopentadiene. The potential uses of ferrocene are as an additive to gasoline to prevent engine knock and as an additive to diesel fuel to facilitate trap regeneration. The presentation on ferrocene focused on work done at the Fraunhofer Institute to characterize exhaust with and without ferrocene in fuel and to evaluate toxicity. More information about toxicity studies of ferrocene can be found in the following references: (1) “Investigation of Otto Engine Exhaust Resulting from the Combustion of Fuel with Added Ferrocene,” a report from the Fraunhofer Institut für Toxikologie and Aerosolforschung (July 1996); (2) “Thirteen-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F1 Mice,” Nikula, KJ et al., in Fund. Appl. Toxicol. 21, 127-139 (1993).

Dr. Hartwig Muhle (Fraunhofer Institute) presented work done at the Fraunhofer Institute to compare a commercial fuel containing 30 ppm ferrocene with a fuel not containing ferrocene. This work involved chemical and physical characterization of exhaust, studies of exhaust fractions in in vitro mutagenicity and cytotoxicity assays, and animal inhalation studies of chronic toxicity and carcinogenicity. Exhaust was produced by a VW Golf/Passat 1.8 l engine with automatic transmission and catalytic converter. The driving cycle involved urban and freeway driving with an average speed of 40 mph and a maximum speed of 80 mph.

Emissions testing was for particle mass, size distribution and concentration; for eight hydrocarbons, 16 polycyclic aromatic hydrocarbons, five aldehydes; for the sum of phenols, ammonia, iron and platinum; and for oxides of nitrogen and carbon. Results indicated that, with ferrocene, the median mass aerodynamic diameter (MMAD) was somewhat decreased and the size distribution of particles narrowed. Other characteristics of the exhaust did not appear to be changed by the addition of ferrocene.

The fractions studied for mutagenicity and cytotoxicity were exhaust condensate, particles, toluene-soluble extracts from the particles, and the gaseous phase of the exhaust. Both mammalian (hamster lung cell line) and bacterial test systems (Ames test for mutagenicity) were used. Because of the low particle concentration, a new particle collection device had to be designed. Under the testing conditions used, ferrocene did not affect the cytotoxicity or mutagenicity (in four tester strains of Salmonella) of exhaust.

Animal testing involved exposure of rats to the highest technically feasible exhaust concentrations (a 1:20 dilution of exhaust), a 1:40 dilution, and a clean air control. Exhaust was diluted in order to avoid carbon monoxide poisoning. Animals were exposed for 18 hours/day, 5 days/week for 12 months (for chronic toxicity), or for 24 months + 6 months recovery (for carcinogenicity). Pulmonary end points included particle retention, lung clearance, biochemical and cytological measurements in bronchial lavage fluid, and mechanical lung function. Histopathology, clinical chemistry, and urinanalysis were also conducted. Animals exposed to exhaust from ferrocene-containing fuel did not respond differently than those exposed to fuels not containing ferrocene. No toxic effects were observed after 24-30 months.

Cerium

Rhodia Inc. is developing a cerium-containing additive to add to diesel fuel in an on-board injection system in conjunction with a particulate trap. The additive would act as a catalyst to promote efficient combustion of trapped particles. The presentation at the workshop focused on the effectiveness of cerium in conjunction with the trap in reducing particulate emissions. There has also been some toxicologic evaluation of ceric oxide. Rhône-Poulenc has funded toxicity studies of ceric oxide, including a 13-week inhalation study in rats in which the lowest observed effect level (LOEL) was 5 mg/m3. Effects at that concentration included pigment accumulation in the respiratory tract, laryngeal metaplasia, and lymphoid hyperplasia. A reference concentration for ceric oxide (estimate of the daily exposure to humans that is likely to be without appreciable risk over a lifetime) was calculated to be 0.24 mg/m3 ceric oxide, based on the same study. Mutagenicity results were reported to be negative in the Ames test. A report by Radian Corporation, “Risk Assessment of Ceric Oxide Emissions Due to the Use of a Rhône-Poulenc Fuel Additive,” Edition II (1994), provides information on toxicity studies of cerium.

Dr. Hartwig Muhle and Mr. Jacques Lemaire, Rhodia Inc., discussed results of studies looking at the effects of cerium on the size and distribution of particles found in diesel exhaust. More than 90% of the cerium added to diesel fuel is retained in the particle trap as cerium oxide. The particle trap is cleaned after approximately 150,000 km of driving through a reverse air flow system that collects material in a bag.

Mr. Lemaire reported on recent emissions tests illustrating the effectiveness of a cerium-containing additive at 50 or 100 ppm together with a particle trap in reducing the number of particles emitted by 99% (referred to in Report W11/12/97 from Technik Thermische Maschinen, Niederrohrdorf, Switzerland, entitled “VERT—Curtailing Emissions of Diesel Engines in Tunnel sites”). Mr. Lemaire also discussed recent action by the German environmental protection agency (Umweltbundesamt or UBA) to approve the use of the additive and trap.

Platinum

Platinum, palladium, and rhodium are used in catalytic converters in cars to reduce emissions of carbon monoxide, hydrocarbons, and nitrogen oxides. In cars using catalytic converters containing platinum, ultrafine platinum is released at low levels during combustion. Tailpipe emissions contain platinum attached to carrier particles of aluminum oxide (Al2O3 ). An important issue in understanding toxicity is the bioavailability of the inhaled platinum to cells.

Dr. Muhle reported on studies of platinum bioavailability derived from the automotive exhaust of cars using catalytic converters containing platinum. He described how model particles containing platinum were prepared by chemical methods. To investigate the bioavailability of platinum, Lewis rats were exposed by intratracheal instillation to 2- 20 mg of the model particles (Al2O3 particles containing 3% platinum) or to 0.3 or 0.6 mg of pure platinum particles. Animals were sacrificed after 1, 7, 28, and 90 days and the body burden of particles determined. Results indicated that the bioavailable portion of the retained platinum (that found in urine and organs) comprised 5-15% (model particles) or 0.8% (pure platinum) of the total instilled platinum.

In an inhalation study to further investigate bioavailability, Lewis rats were exposed 5 hr/day, 5 days/week for 3 months to 4 mg/m3 or 12 mg/m3 of a test aerosol (Al2O3 particles with 2.7% metallic platinum on the surface). Animals were sacrificed 1 day after the end of the exposure. About 30% of the retained platinum in lungs was found in urine and organs. Thus, a significant fraction of the inhaled platinum may be bioavailable.

Non-Tailpipe Emissions of Metals

This presentation drew attention to emissions other than tailpipe emissions as potentially being significant sources of exposure to metals.

Dr. Steven Cadle (General Motors Corporation) noted that there are significant PM-containing emissions from automobiles in addition to tailpipe emissions, and suggested that some attention should be paid to the potential exposure to and health effects of non-tailpipe emissions. These include emissions from brake wear and tire wear, and fugitive emissions. Many metals are associated with particles in emissions. In tailpipe emissions, metals include magnesium, aluminum, calcium, iron, copper, zinc, and lead. Some of these are emitted in very small amounts. Dr. Cadle also presented data on the composition of brake pads, which may contain the following metals: aluminum, antimony, copper, iron, calcium, zirconium, and titanium. They also contain a variety of other material, such as dust from cashew nuts, phenolic resin, and powdered rubber.

THE CASE OF MMT

Methylcyclopentadienyl manganese tricarbonyl (MMT) is a manganese-containing organic compound that has previously been used in gasoline in the United States and Canada. Currently, as a result of a court decision, it is available for use in fuel in the United States, and will soon be available again in Canada. MMT acts as an octane booster and may reduce NOx emissions. Its introduction into fuel is controversial however, because individuals exposed to high levels of manganese over long periods of time exhibit neurotoxic symptoms. The impact of long-term exposure to lower levels of manganese that may be present in emissions from autos using MMT in fuel has not been fully evaluated. A further concern has been whether MMT would affect the catalytic converter and increase levels of tailpipe emissions. In addition, those opposing the use of MMT cite lessons learned in the past from the use of lead in fuel. Toxicologic and epidemiologic testing to address health concerns about MMT is now under way. However, consensus has not been reached about whether the testing will adequately address the health concerns.

The use of MMT is an important issue in its own right. In addition, it serves to illustrate the concerns that accompany the introduction of any fuel additive or technology that has the potential of adding additional metal compounds to the ambient environment. Thus, the presentations of a number of experts in this area served to illuminate not only the issues about manganese per se, but the various perspectives that must be taken into consideration before the widespread introduction of a new additive.

Introduction

At low levels manganese is an essential trace element required for many enzymes, some of which are important for CNS function, particularly in the brain of the developing infant; however, long-term exposure to higher levels is associated with manganism, a condition similar to but not identical to Parkinson's disease. Adults typically ingest 0.7 11 mg of manganese per day in their diets, often from tea and many common cereal products and may ingest an additional 10 to 50 mg by taking dietary supplement tablets. In addition, exposure to manganese can occur by ingestion of surface or tap water, and by breathing the air on paved and unpaved roads.

Understanding manganese toxicity has come primarily from occupational health studies. Manganese is used primarily in the generation of steel and to a lesser extent in the production of dry cell batteries. Long-term worker exposure to manganese dust can result in a neurological syndrome (“manganism”) similar to but distinguishable from Parkinson's disease. Manganese interacts with the dopaminergic system and in manganism, primary neuropathological changes are observed in the basal ganglia, particularly in the globus pallidus, believed to be high in dopaminergic receptors.

The Use of Manganese in Fuel and the Manganese Toronto Exposure Study

Dr. Ben Fort Jr., Ethyl Corporation, described his company's work with MMT. Used at the level of 0.031 gm/gallon, MMT not only acts as an octane enhancer, but also decreases automotive NOx emissions by 20%. It was used in leaded and unleaded gas in the United States in the early `70s, and has been used in unleaded gas in Canada since 1977. Ethyl set up a 15-month study in a non-occupationally exposed population in Toronto, a city in which MMT has been added to gasoline, conducted by Edo Pellizzari of Research Triangle Institute. The probability-based study provided an estimate of the frequency distribution of exposures to manganese. Preliminary results for exposure to manganese in PM2.5 (Mn- PM2.5) were: 50th percentile - 0.0085 g/m3, 95th percentile - 0.0163 g/m3, and 99th- 0.0215 g/m3, indicating that exposures are below the reference concentration (RfC). Dr. Fort pointed out that the study found a negative correlation between the average concentration of manganese in gasoline and the average personal exposure (measured as Mn- PM2.5 and Mn-PM10).

MMT Emissions Characterization

Dr. John Reynolds, Lawrence Livermore National Labs, characterized tailpipe emissions from seven different automobiles using MMT in their gasoline. Dr. Reynolds used Electron Spectroscopy for Chemical Analysis (ESCA), which gives information about elemental composition and concentration, Auger Electron Spectroscopy, which provides information about the chemical environment, and x-ray absorption spectroscopy (XAS, XANES, EXAFS), which provides information about valence state and local structure. Comparing spectra of test samples with those of standard manganese-containing compounds, his team found that the majority of the manganese was in the oxidation state II, and that a mixture of manganese phosphates and sulfate fit the emissions characteristics best. In the tier two testing, more extensive XAS data were obtained showing that manganese oxides appeared to constitute only a small fraction of the manganese in the emissions. Thus, under the conditions tested, Dr. Reynolds suggested that the major manganese-containing combustion product was a phosphate (and/or sulfate), rather than an oxide as had previously been reported. He thought that the phosphate was probably derived from engine oil, and the sulfur from gasoline. Dr. Reynolds also found that the bulk of the manganese was in aerosol size fractions of approximate MMAD 1.8 microns, but there were several other size fractions.

Proposed Animal Studies of Manganese Phosphate

Dr. David Dorman, Chemical Industry Institute of Toxicology, described how prominent species differences in brain anatomy, regional brain manganese delivery, and neurotoxicologic response occur between rats and primates. Dr. Dorman presented an overview of the design of a series of studies sponsored by Ethyl Corporation, which will evaluate the pharmacokinetics of inhaled manganese phosphate in male and female adult CD rats, aged male CD rats, and adult male rhesus monkeys. Although small amounts of the sulfate and oxide forms may be produced, the primary combustion product of MMT appears to be manganese phosphate. Short-term (14-day) inhalation exposures will be conducted in rats with manganese phosphate, manganese sulfate, and manganese oxide (Mn3O4) to evaluate how the chemical form influences manganese pharmacokinetics. The studies will examine the tissue pharmacokinetics following inhalation to 0.03, 0.3 and 3 mg/m3 manganese. Even the lowest of these levels is more than 1000-fold higher than those measured in air where MMT is used in fuel. Dr. Dorman described that the partitioning of manganese into blood and tissue compartments is route-specific and that this area is the subject of ongoing research. CIIT is investigating whether axonal transport of manganese by the olfactory nerve to the brain occurs following manganese inhalation. Another goal of this research project is to determine how manganese is partitioned in blood and possible target tissues of CD rats following exposure to manganese via toxicologically relevant routes (i.e., ingestion or inhalation). Dr. Dorman's research group has recently completed the 14-day manganese phosphate inhalation study in rats. An MMAD particle size of 1.8 mm was used to replicate the size of manganese-containing particles derived from tailpipe emissions. The final design of these studies is the subject of ongoing negotiations between the U.S. EPA and Ethyl Corporation.

Potential Issues Concerning MMT Use

Dr. Ellen Silbergeld, University of Maryland Medical School, presented the view that currently there are insufficient data to accept the safety of MMT as a fuel additive, particularly in light of the problems that resulted from the widespread use of tetraethyl lead. While recognizing that there are differences between lead and manganese (e.g. lead is wholly toxic whereas manganese is an essential trace element, lead is divalent under physiologic conditions whereas manganese is in multiple valence states [2, 3 or 4]), Dr. Silbergeld thought that there were multiple lessons to be learned about MMT from findings with previous lead use in gasoline. In her opinion, no untested or inadequately tested chemical should be used, produced, or intentionally released. Dr. Silbergeld pointed out that a survey of new chemicals indicated that 86% had not been tested for immunotoxicity, 33% for neurotoxicity, 90% for developmental toxicity, and 53% for chronic toxicity.

Dr. Silbergeld thought that information was needed in several areas for MMT:

Dr. Silbergeld commented that most clinical studies of manganese were less useful than they could be because they studied overt disease. She emphasized taking a mechanistic approach as the key to understanding manganese toxicity. One approach that Dr. Silbergeld recommended was to take explants of different brain regions and study them in vitro. Dr. Silbergeld stressed the use of appropriate animal models, routes of exposure, and endpoints, and tests of appropriate sensitivity and power to study the neurotoxic effects of manganese exposure. She thought that sub-primate animals were not appropriate models for this type of testing. She added that once effects were localized in human brains, relevant mechanistic studies could probably be conducted in sub-primate animal models (rodents).

EPA's Approach to Regulating Exposure to MMT

Dr. J. Michael Davis, National Center for Environmental Assessment, U.S. EPA, discussed the approaches that the U.S. EPA has taken to characterize the potential health risks of manganese. One aspect of this effort involved setting an inhalation reference concentration, which he stressed was not “a bright line” between what is safe and what is not; even at exposures above the RfC, health risk is undetermined. The current RfC, 0.05 mg/m3 manganese, was derived from an occupational study of battery plant workers conducted by Harry Roels and colleagues in Belgium. A LOAEL (lowest observed adverse effect level) of 50 mg/m3 manganese (after adjustment to reflect continuous, non-occupational exposure) was divided by a total uncertainty factor of 103, allowing 10 for each of three factors: 1) potentially greater susceptibility of special populations such as the elderly and young; 2) extrapolation from a LOAEL to a NOAEL (no observed adverse effect level); 3) several specific data base limitations. EPA also investigated alternative approaches for the exposure-response analyses and for estimating an RfC. Leading candidate RfC estimates from these alternative approaches were in the range of 0.09 to 0.2 mg/m3 manganese . Dr. Davis noted that numerous assumptions and limitations in the data became evident in conducting these analyses. In response to a question, Dr. Davis acknowledged that the RfC for inhalation was at a level below the recommended daily dietary intake of manganese, but commented that one could not assume that toxicity via the inhalation route was the same as via ingestion.

The EPA assessment included an exposure analysis based on the Particle Total Exposure Assessment Methodology (PTEAM) study that was conducted in Riverside, CA, in 1990, when MMT was used in leaded gasoline. Based on this study and other information, EPA projected possible distributions of personal exposure levels to particulate manganese assuming 100% usage of MMT in unleaded gasoline. The 90-95th percentile exposure levels in these distributions were estimated at approximately 0.1 mg/m3 manganese.

Dr. Davis noted several key research needs for MMT :

Dr. Davis noted that EPA, under authority of Section 211 of the Clean Air Act, expects to require Ethyl Corporation to conduct studies that will help address these issues.

 

Home | About HEI | What's New? | Newsletter | HEI International | Publications
Research | Funding | Meetings | Contact HEI | Links | Search | Site Map
Copyright © 2004 Health Effects Institute. Please send comments to webmaster@healtheffects.org