Environmental Health Perspectives (EHP) is a monthly journal of peer-reviewed research and news on the impact of the environment on human health. EHP is published by the National Institute of Environmental Health Sciences and its content is free online. Print issues are available by paid subscription.DISCLAIMER
A hot, steamy day combined with nitrogen oxides and volatile organic compounds can result in excess ozone levels and respiratory distress for millions of people, not only in major cities like Houston and Los Angeles, but anywhere sunshine and pollution meet. The most vulnerable people are sensitive individuals such as asthmatics, children, and the elderly, although chronic exposure to ozone may lead to impaired health for anyone. The first Focus article reviews the data from epidemiological and animal studies and addresses the potential need for the EPA to reevaluate the current National Ambient Air Quality Standards for ozone.
Methyl tertiary butyl ether (MTBE) is added to gasoline in some U.S. cities to reduce carbon monoxide emissions in the winter months. There is disagreement about both the efficacy and the toxicity of MTBE. The second Focus article examines epidemiological studies in Alaska, Connecticut, and New Jersey with respect to MTBE-related symptomology, as well as human laboratory studies to determine potential relationships between relevant concentrations of MTBE exposure and toxicity. Questions about anecdotal evidence of health effects, potentially sensitive populations, and mixtures of toxicants and MTBE in gasoline are prompting researchers to study whether MTBE is a health benefit or burden.
The Innovations article on p. 676 describes the Atmospheric Studies in Complex Terrain (ASCOT) program of the Department of Energy. Researchers in this program are modeling the windborne distribution of pollutants, and of radioactive waste in the event of a nuclear disaster in the Tennessee Valley near Oak Ridge, or in the Rocky Flats area near Denver, Colorado. Both of these locations are geographically unique and display complex circulation patterns due to the proximity of mountains to valleys, slopes, and plains. Researchers and emergency response planners hope that complex terrain modeling will help determine suitable evacuation routes and limit health risks in the event of a toxic release.
Up until now, chemicals selected for chronic rodent bioassays have been chosen because they were suspect carcinogens, although only 92 of the 400 chemicals selected (23%) were positive in two species. Many other chemicals have been selected for testing based on production volumes or widespread exposure to the human population, and nearly 80% of these 133 chemicals were noncarcinogenic, even when tested at the maximum tolerated dose; only 9 of these chemicals were positive for carcinogenicity in both species of rats and mice. Based on these retrospective data, Fung et al. predict that less than 10% of the 75,000 chemicals in commercial use would be positive in two species and thus be considered likely to pose a carcinogenic hazard to humans.
EHP has been the forum for an ongoing debate concerning the legitimacy of using Taiwanese data for estimating arsenic cancer risks outside of Taiwan. Mushak and Crocetti outline the arguments for and against current cancer risk estimates for ingested inorganic arsenic. Arsenic in food crops like rice and sweet potatoes may be subject to overestimation due to the chemical extraction techniques, and estimates of arsenic ingestion from well water may also be incorrect due to overestimation of water consumption. Recent findings that arsenic was associated with internal cancers in the Taiwanese suggest the need to reevaluate permissible ingestion levels for inorganic arsenic.
Chlordane is a persistent, dangerous pesticide that was applied to an estimated 30 million homes in the United States. In 1987, 250 adults and children were exposed to chlordane after an apartment complex was sprayed. In 1994, Kilburn and Thorton measured neurobehavioral function in 216 of the exposed adults and collected questionnaires on symptom frequency, mood status, and rheumatic and respiratory disorders. Exposure was associated with protracted impairment of neurophysiological and psychological functions that had persisted for 7 years.
Standeven et al. tested unleaded gasoline vapor as a liver tumor promoter. Male B6C3F1 mice were initiated with N-nitrosodiethylamine (DEN) at 12 days of age and exposed by inhalation to 2046 ppm unleaded gasoline starting at 5-7 weeks of age for 6 hours per day, 5 days per week, for 16 weeks. There was a 2.3-fold increase in liver tumors in DEN-initiated mice and no liver tumors in noninitiated mice. Promotion of DEN-initiated altered liver foci in male mice was associated with a selective increase in the proliferation of focal liver cells, an effect that was not detected in a chronic bioassay of mice exposed to unleaded gasoline alone.
A three-dimensional quantitative structure-activity model was used to examine a number of chlorinated hydroxybiphenyl analogs known to bind to the estrogen receptor. Waller et al. showed that specific characteristics of the chemicals, including the phenolic ring system, conformational restriction of the overall structure, and its hydrophobic character, were necessary for establishing optimum binding affinity to the estrogen receptor. Molecular computer models are becoming increasingly useful for determining potential estrogenic activity of a wide range of phenyl-substituted chemicals.
Female rats treated for one week with diethylstilbestrol, genistein, or DDT exhibited enhanced epithelial cell proliferation and differentiation of the mammary glands, acting to promote the maturation of undifferentiated terminal end buds to more differentiated lobular terminal ductal structures. Brown and Lamartiniere showed that similar treatment with dioxin inhibited these cellular processes, probably because of toxicity or antiestrogenic action or a combination of both.
Respiratory function and symptoms and particulate air pollutants were evaluated in three different communities located near a biomedical incinerator, a municipal waste incinerator, or a liquid hazardous waste-burning furnace. Shy et al. found that daily concentrations of fine air particulates varied as much as 8-fold within the same community and were not different between communities. A large, one-time, baseline descriptive survey revealed no consistent community differences in the prevalence of chronic or acute respiratory symptoms when compared to reference communities. There was no indication that the proximity of neighborhoods to waste incinerators was associated with respiratory irritation or depressed lung function.
Perkins et al. used a pharmacokinetic model to compare disposition of inhaled methanol in humans to that in mice and rats. The model reported values for methanol concentrations in blood or urine of humans, non-human primates, and rodents after inhalation and predicted that blood methanol would be 13- to 18-fold higher in mice, and 5-fold higher in rats than in humans after 8 hours of exposure to 5000 ppm methanol vapor. The authors emphasize that for risk assessments that use data extrapolated from rodents to humans, it is important to consider blood concentrations rather than vapor exposure concentrations of methanol.
The drug succimer is currently proposed as an oral chelation agent for treatment of heavy metal poisoning. Asiedu et al. evaluated the pharmacokinetics of this drug in lead-exposed children and adults and showed that it undergoes enterohepatic circulation. Microflora in the gut were necessary to metabolize the drug to an active form, implying that simultaneous use of antibiotics with succimer may reduce the efficacy of the drug. The data showed that the 1:2 meso-2,3-dimercaptosuccinic acid:cysteine metabolite of succimer was responsible for lead chelation and that moderate lead exposure impaired drug elimination by the kidney.
Inuit men, women, and children living in Qikiqtarjuaq on Baffin Island in the Eastern Arctic subsist on food items that include ringed seal, bearded seal, narwhal, beluga, walrus, polar bear, caribou, Artic char, mussels, kelp, blackberries, and greens. Chan et al. reports elevated concentrations of mercury, cadmium, and lead in these foods. Based on normal daily food consumption, these values were in excess of tolerable daily intake levels established by the World Health Organization. Ringed seal meat, caribou meat, and kelp were the items primarily contributing to the elevated intake of heavy metals.
Tarter et al. presents a new form of regression for application to environmental studies. The goal of conditional switching regression is the estimation of a proportion of responses between, for instance, unsensitized and sensitized individuals. For example, this approach could be valuable in determining whether an asthma attack occurs in response to a given chemical concentration by measuring a continuous spectrum of binary values, rather than measuring the severity of the attack.