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In December 1990 the U.S. Environmental Protection Agency sponsored a workshop to discuss the applicability of an interim "toxicity equivalency factor" (TEF) approach to assessing risks posed by exposures to complex mixtures of polychlorinated biphenyls (PCBs). The group concluded that application of the TEF approach to PCBs would be less straightforward than it was in the case of chlorinated dibenzo-p-dioxins and dibenzofurans (CDDs/CDFs). It appears that "dioxin"-like properties of some PCB congeners are amenable to a TEF treatment that is compatible with that used for CDDs/CDFs. Such a scheme also seems to have utility in assessing risks to wildlife. Other non-"dioxin"-like toxic endpoints (e.g., neurotoxicity) appear to have a different structure-activity-related mechanism-of-action that requires a separate TEF scheme. The workshop identified data gaps in toxicology and analytical chemistry that hinder adoption of proposed TEF schemes for PCBs at this time.

The racial stratification of residues of total DDT equivalent, heptachlor epoxide, oxychlordane, dieldrin, beta-benzene hexachloride and lindane in human adipose tissue was studied. Samples of human adipose tissue were obtained from locations selected in the contiguous United States according to a stratified, proportionate-random survey design and chemically analyzed for selected organochlorine pesticides. The most marked case of racial difference in residue level was total DDT equivalent. Samples from Negros contained almost twice as much of this chemical as did samples from Caucasians. Racial stratification also was found in the frequency of lindane. Lindane was detected about twice as often in samples from Negros than in samples from Caucasians. Little racial differences were noted for residues of beta-benzene hexachloride, heptachlor epoxide, dieldrin and oxychlordane.

Agricultural uses of the insecticide DDT were cancelled by the U.S. Environmental Protection Agency December 31, 1972. However, the domestic use of DDT had begun to decline before this action. Beginning July 1969, residues of DDT and its metabolites were measured in human adipose tissue collected through an annual national survey. Levels of total DDT equivalent residues in human adipose have decreased slightly, but the frequencies of finding DDT or its metabolites have remained high. The most marked decline in residue concentration has been found in the youngest age group (0-14 years). Approximately 80 percent of the total DDT equivalent found in this survey was DDE. These data show that the reduction of the agricultural uses of DDT has decreased human exposure to and storage of this chemical.

Hexachlorobenzene (HCB) is a chemical of concern to the US Environmental Protection Agency. Although the use of HCB as a fungicide has virtually been eliminated, detectable levels of HCB are still found in nearly all people in the USA. This paper describes an examination of HCB-residue levels from the US National Human Adipose Tissue Survey, which is an annual programme to collect a nationwide sample of adipose-tissue specimens and analyse them for the presence of toxic compounds. The specimens are collected from surgical patients and autopsied cadavers according to a multistage statistical survey design that allows identification of geographic and demographic subpopulations with elevated HCB levels, and thus may help to indicate sources of human exposure to this chemical. Data on HCB body-burden levels are available for the years 1974-1983, excluding 1980 and 1982. The estimated average residue level of 6115 specimens is 0.053 ppm, the ninetieth percentile value is 0.09 ppm and the range is 'not detected' to 4.33 ppm. The analysis reveals that while the percentage of individuals with detectable levels is increasing, the annual average level is decreasing. A large percentage of specimens with elevated HCB levels comes from the Pacific census division and the oldest age group. In comparison, world-wide detectable levels are approaching 100% and average residue levels tend to increase with age. World-wide HCB levels are higher in females, which contrasts with findings from the National Human Adipose Tissue Survey.