Interspecies Variation in Risk Assessment
Traditionally, all animal model data extrapolated to humans used a 10-fold uncertainty factor in risk estimates to account for the greater sensitivity of humans to toxicants. Calabrese and Baldwin (p. 14) present a novel risk assessment model based on acute toxicity in fish that suggests variation in toxic response between all vertebrates can be quantified, yielding a value that depends on the phylogenetic relationship of the species being compared. Their model indicates that most mammalian toxicity studies provide a binary interspecies comparison of orders-within-class categories for human risk assessment, yielding a 65-fold rather than a 10-fold uncertainty factor for risk estimation.
Toxicity of Nerve Gases
Munro et al. (p. 18) review the acute, chronic, and delayed toxicity of three organophosphorous nerve agents, GA, GB, and VX, developed as chemical warfare agents. The disposal of these agents by incineration is underway by the U.S. Army Chemical Stockpile Disposal Program. These nerve agents can cause immediate death by respiratory failure. There is no evidence from animal tests that nonlethal doses of these chemicals causes delayed neuropathy, teratogenesis, or other developmental and reproductive effects. However, because acute exposure to nonlethal doses results in diminished mental acuity, it is paramount that the public is warned early in the unlikely event of inadvertent release of these agents.
Desert to Arctic Conditions in 4800-ft
3
Research Biosphere
A novel environmental simulation laboratory referred to as the "sand box" or "box of rocks" was built to enable environmental scientists to study the effects of weathering in areas ranging from permeability of oil shale waste to microbial degradation of toxicants (p. 60). In the computer-controlled laboratory, scientists can determine the effects of environmental conditions on different physical or biological processes by varying the temperature from -15°C to 120°C, raising the relative humidity to 100%, duplicating sunshine with metal halide lamps, and simulating 5 inches of rainfall per hour. The megalab may be used to research issues of national importance such as protection and cleanup of groundwater, remediation of contaminated landscapes, and improved solid and hazardous waste disposal.
Cocarcinogenicity of Radon and Pollutants
Radon and radon daughters cause cancer in uranium miners. Monchaux et al. (p. 64) showed that when rats are exposed to a combination of radon and tobacco smoke, a two- to fourfold increase in lung cancer occurred, while intrapleural injection of mineral fibers plus radon resulted in an additive increase in lung tumors. Inhalation of diesel exhausts or minerals present in metallic ores did not enhance tumorigenesis in combination with radon. Monchaux et al. suggest that this rodent model of cocarcinogenicity could be used for studies of potential carcinogens that might be present in occupational settings.
Nursing Mothers Transfer Methylmercury to Infants
Grandjean et al. (p. 74) selected a cohort of infants from the Faroe Islands to measure the burden of methylmercury transferred in human milk. The diet of the Faroese population, located between Scotland and Iceland, consists largely of seafood and contains high levels of methylmercury. The concentration of mercury in hair was proportional to the length of breast-feeding and was highest in babies that had been breast fed 12 months. The data suggest that elimination of mercury is slow or nonexistent during the first year after birth. The authors suggest that because there might be an increased risk of methylmercury neurotoxicity associated with prolonged breast-feeding, mothers in the Faroe Islands should discontinue breast-feeding when their children are 6 months old.
Modeling Cadmium Toxicokinetics
Slob and Krajnc (p. 78) suggest that interindividual variation be included in models to improve risk estimates from exposure to cadmium. Usually, toxicokinetic models that calculate risk from exposure use average values to estimate internal doses based on external doses (e.g., these models use average body weight, average food intake, and so forth). Because individuals vary widely, use of a "standard human" to calculate risk may not provide adequate protection. A case study for cadmium exposure is used to quantify various sources of normal interindividual human variation, so that these data can be incorporated into a model for risk analysis that includes broader segments of the population.
Chronic Skin Bioassays of Petroleum Refinery Streams
A six-month initiation-promotion bioassay of petroleum refinery streams in CD-1 mice was qualitatively predictive for mouse skin tumors resulting from two-year skin paint studies in C3H/HeJ mice. Skisak et al. (p. 82) investigated nine different petroleum refinery streams of varying volatility and composition. Middle distillates were weakly carcinogenic after two years and acted as promoters. Untreated mineral oil streams were initiators and were carcinogenic after two years, presumably because they contain polycylic aromatic hydrocarbons of requisite size and structure. The most and least volatile of the streams, and sweetened naphtha, were noncarcinogenic in both assays.
Discriminate Mutagenesis by Near-UV Radiation
Tester strains of
E. coli
with single or double mutations for loss of superoxide dismutase exhibited distinctive mutagenic spectra. Knowles and Eisenstark (p. 88) report increased G:C to A:T transitions and G:C to T:A and A:T to T:A transversions in the DNA of wild-type
E. coli
exposed to near- UV radiation. Double mutants of
E. coli
exposed to near-UV radiation exhibited greater mutation frequency and other unusual spontaneous mutation spectra compared to single mutants, suggesting that near-UV mutagenesis and superoxide anion-dependent mutagenesis involve different lesions and/or mechanisms.
Arylamine-Hydroxyanisole Product Mutagenicity
Kalus et al. (p. 96) identified and characterized products of model reactions between the food preservatives butylated hyroxyanisole (BHA),
tert
-butylquinone, or
tert
-butylhydroquinone and the arylamines aniline and
N
-methylaniline. BHA and the quinoid metabolites protected against the formation of carcinogenic compounds like
N
-nitroso-
N
-methylamine, since none of the reaction products were mutagenic in
S. typhimurium
strains TA98 or TA100, with or without metabolic activation.
Last Update: August 18, 1997
[
EHIS Home
] [
Search EHP
] [
Comment on article
] [
Tech Assistance
]
[
Subscription Options
] [
Single Copy Order Form
]