Air Toxics

A Special Report of the Institute's Air Toxics Review Panel. Special Report 16 summarizes the health effects of exposure to the 21 mobile-source air toxics (MSATs) defined by the 2001 EPA mobile-source rulemaking and critically analyzes the literature for a subset of seven MSATs (acetaldehyde, acrolein, benzene, 1,3-butadiene, formaldehyde, naphthalene, and polycyclic organic matter). The report also assesses and summarizes research gaps and unresolved questions, as understood in the context of the current regulatory agenda. The report focuses on MSATs for which mobile sources are a sizable source of human exposure and for which existing data suggest that health effects might be observed at concentrations approaching those found in ambient air. For each MSAT, the following questions are addressed: (1) To what extent are mobile sources a significant source of exposure to this MSAT? (2) Does this MSAT affect human health? (3) Does this MSAT affect human health at environmental conditions?

This study by Dr. Elizabeth Delzell and colleagues is the first major update of the most extensive human study to date of potential carcinogenic effects of 1,3-butadiene (BD). The earlier study investigated mortality among the largest occupational group exposed to BD: 18,000 men employed in the styrene-butadiene rubber (SBR) industry between 1944 and 1991. In the current study, these workers were followed for an additional 7 years and the effects of exposure to other compounds were evaluated.

Drs. Yokel and Crossgrove at the University of Kentucky Medical Center studied the mechanisms by which manganese enters and leaves the brain across the blood–brain barrier and, in particular, whether transporter molecules are involved. The investigators used in vivo brain perfusion in rats as well as in vitro tests in several cell lines to assess specific characteristics of manganese transport, such as pH and energy dependence. Manganese transport rates were compared with those of sucrose and dextran, which do not easily cross the blood–brain barrier.

Dr. Albertini and colleges organized a group of researchers from the United States, Czech Republic, The Netherlands, and the United Kingdom to determine whether biomarkers in the blood and urine of workers exposed to butadiene in occupational settings correlated with their personal exposure. Samples were collected from male workers employed either in a plant that used butadiene and styrene to produce rubber polymer in Prague. They also collected blood and urine from male administrative workers at the plant who had no direct occupational exposure to butadiene and served as control subjects.

Drs Turteltaub and Mani at Lawrence Livermore National Laboratory investigated benzene metabolism in rodents over a large dose range that encompassed concentrations close to those of human ambient exposure. Understanding benzene metabolism at low exposure levels is critical to benzene assessment to determine the shape of the dose-response curve at low concentrations.The investigators administered radioactive benzene to mice and rats and subsequently analyzed bone marrow, liver, urine, and plasma from these animals.

This report describes two studies that measured emissions in roadway tunnels. Dr. Alan Gertler and colleagues at the Desert Research Institute studied particulate matter emissions in the Tuscarora Mountain Tunnel located on the Pennsylvania Turnpike. Dr Daniel Grosjean and colleague at DGA, Inc studied carbonyl emissions in the Tuscarora Mountain Tunnel and in the Caldecott Tunnel in California. The unique environment in tunnel studies allows the investigators to measure emission rates averaged over many vehicles, to determine the physical and chemical character of emissions under ambient conditions, and in some instances to compare current emissions with past emissions at the same location. Both groups of investigators also measured emissions at times when the proportions of gasoline engine vehicles and diesel engine vehicles differed, allowing them to estimate the differences between emissions from the two sources.

Dr. Eastmond and colleagures at the University of California, Riverside investigated whether chromosomal changes could be used as biomarkers of benzene exposure in mice and humans. The first part of the study involved detecting chromosomal alterations in cells using a modification of a molecular cytogenetic technique known as fluorescence in situ hybridization (FISH). Eastmond and colleagues evaluated the frequency of such chromosomal aberrations in the erythrocytes (red blood cells) from the bone marrow of mice exposed to various doses of benzene and for different exposure durations.