Sizing up the Chemical Soup
Some of the methods proposed for assessing the risks of chemical mixtures are described in this month's Focus article (p. 142). These methods include using additive or synergistic models of toxicity, using toxic equivalency factors for selected chemicals, and using models for pharmacokinetic or pharmacodynamic interactions. The need to address the real-world scenario of multiple contaminant exposure to tobacco smoke, internal engine combustion products, multiple chlorinated agents, dioxin by-products, etc., presents a new and important challenge for toxicologists and regulators.
Science in the Court
The search for truth in science and in law can become a philosophical battlefield and a practical nightmare when the two disciplines collide in the courtroom. The Spheres of Influence (p. 146) examines some of the efforts being taken by members of both professions to address the issues surrounding the use of scientific evidence and experts in legal trials. Efforts underway include a reference manual for judges on scientific methods and the peer review process to help them assess scientific evidence, establishment of guidelines for using court-appointed scientific experts and special masters, and identification of the characteristics of potential sources of toxic tort litigation to aid judges in case management.
Surfing the Net
The wave of the future is known as the Internet, a computer-linked gateway to a sea of information. Seasoned users refer to "surfing the net," i.e., searching through the Internet to connect with a world of sources for information on almost any desired topic. The Innovations article (p. 148) presents the latest developments in using the Internet to conduct scientific research: BIOMOOs and collaboratories link scientists across the country and around the world. Science is now on-line. Incidentally, "EHPnet" will become a regular feature of the Environews section of EHP, highlighting where and how to find items of interest about environmental health on the Internet. EHP will be available on-line on the Internet in 1995.
Sand in Your Craw?
Since crystalline silica was labeled a probable carcinogen, warning labels on sand and related products have been required, and time, money, and effort have been expended to quantitate risks from low exposure. Hardy and Weill (p. 152) contend that it is unlikely that uncertainties in risk estimates for silica will diminish and that there is little value in calculating such estimates because unavoidable exposure to the ubiquitous mineral will continue whatever the experimental outcome. They argue that limited regulatory resources should be targeted at occupational exposures that pose higher risk.
Smoking Causes Cancer, Period
Vineis and Caporaso (p. 156) examine a body of evidence that collectively supports a causal nature for an association between smoking and cancer. They cite as examples tumor induction in animals by tobacco smoke and extracts, suggestive molecular epidemiology data for oncogene and tumor-suppressor gene mutations in smokers, and the occurrence of adducts between DNA and tobacco extract chemicals in the lungs and bladder of smokers. They also acknowledge that differences in metabolic capability among people play a role in modulating an individual's susceptibility to tobacco carcinogens.
PCBs Render Harbor Seals Vulnerable to Infections
Mass mortality among marine mammals has become an alarming occurrence in recent years. Ross et al. (p. 162) conducted a two-year feeding study and reported that captive harbor seals fed herring laced with sea water from the polluted Baltic Sea exhibited contaminant-induced immunosuppression, as measured by in vivo delayed-type hypersensitivity reactions. PCBs were mainly implicated in the immunotoxic responses: arylhydrocarbon receptor-dependent toxic equivalent profiles were demonstrated in seal blubber biopsies. The authors hypothesize that certain ocean pollutants may reduce the immunocompetence of marine mammals so that they cannot ward off viral or bacterial infections.
Catfish Tumors Reflect PAH Levels
High levels of polycyclic aromatic hydrocarbons were discharged from a steel coking plant into the Black River in Ohio. A sharp decline in steel production and subsequent plant closure in 1983 resulted in the rapid decline of PAHs in sediment and in brown bullhead catfish sampled from the river. Baumann and Harshbarger (p. 168) report a coincidental reduction in the prevalence of liver cancer and proliferative lesions in catfish between 1982 and 1987. The data were age-dependent and suggest a strong association between PAH exposure and induction of liver cancer in catfish. The study also demonstrates the efficacy of natural remediation after elimination of the source of contaminant.
The Fine Art of Particle Generation
Sioutas et al. previously developed and evaluated different kinds of particle generators to use in animal inhalation studies of risk assessment and environmental toxicology. The generator they describe here (p. 172) was designed to adequately control exposures to mixtures of ambient particles of typical air contaminants (polycyclic aromatic hydrocarbons, heavy metals, quartz, sulfate, etc.) and to obtain accurate dose-response assessments. The system provides a 25 to 30-fold increase in aerosol concentration while maintaining physicochemical characteristics and equilibria with the gas-phase pollutants.
COMPACT Carcinogenicity
Lewis et al. (p. 178) evaluate a computer- based program called COMPACT to identify potential carcinogens based on metabolic information about chemicals. The procedure is based on an estimation of the ability of a chemical to act as an inducer or substrate for certain cytochrome P450 metabolic enzymes (CYP1 and CYP2E). The authors measured the accuracy of COMPACT predictions by comparing them with National Toxicology Program rodent carcinogenicity test data. When COMPACT was based solely on CYP1 specificity, it was 58% correct, while including CYP2E specificity increased concordance with rodent carcinogenicity data to 72%. A combination of the COMPACT program with another structural alert program, Hazardexpert, further increased concordance with NTP test results to 86%.
