Drinking Water and Health, Volume 6 (1986) / Chapter Skim
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1. Executive Summary
1. Executive Summary
Pages 1-10
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From page 1... ...
Wherever data were adequate, however, the committee also developed risk assessments for noncancer end points. In 1977, the first volume of this series contained the advice that both carcinogenicity and other health effects should be evaluated when studying exposures to contaminants in drinking water and elsewhere.
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From page 2... ...
Major factors that influence developmental toxicity include timing of exposure and different patterns of dose response for growth retardation, embryo death, and teratogenicity in laboratory animals. These must all be considered when examining data from mammalian, nonmammalian, and in vitro studies to estimate human risks from developmental toxicants.
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From page 3... ...
Mutagenic activity in the germ cells of test animals must be regarded as evidence of potential germ cell toxicity in people. Demonstrated ability to cause somatic cell mutation, combined with evidence that a substance can reach and interact with the germ cells, is evidence of potential mutagenicity in humans.
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From page 4... ...
As with developmental and reproductive toxicity, major considerations affecting risk assessment for neurotoxicants include the permanence of effects, the amount and timing of exposure, the mechanisms underlying the toxicity, and heightened sensitivity of various subpopulations. Also, as for other chronic noncancer diseases, neurological impairment has rarely been studied in humans (with the important exception of lead-poisoning studies and the adverse effects of a few clinical agents)
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From page 5... ...
Suppression of the immune response typically produces decreased resistance to viruses, parasites, bacteria, and tumor cell grafts, whereas enhancement results in the development of autoimmune diseases and hypersensitivity reactions. The most widely used tests for carcinogen evaluation and regulation are long-term animal bioassays, which are considered to be qualitative predictors of response in humans.
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From page 6... ...
The committee found that inhalation studies, in which chemicals are absorbed at fairly uniform rates over a specified exposure period, are not very different from ideally designed drinking water studies, in which chemicals are absorbed at a variable but moderate rate over the course of a day. In fact, well-designed inhalation toxicity studies may serve as excellent experimental models for deriving drinking water standards for a variety of volatile chemicals.
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From page 7... ...
Epidemiological studies are of value principally for conducting qualitative risk assessments of specific chemicals or industrial processes. Quantitative risk assessments are possible only when the data have been generated in well-conducted studies of well-defined cohorts whose exposures to a specific substance have been carefully measured or estimated and when sufficient time has elapsed from first exposure to the expression of disease.
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From page 8... ...
The committee relied on conversion factors based on body surface area rather than on body weight for extrapolating animal data to humans, since effects have been more directly correlated to that factor in cancer chemotherapy studies. For the noncancer end points considered by the committee, much additional work must be done, both in the identification of suitable animal models for estimating human risk and in the development of theoretical models for using animal data, once obtained.
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From page 9... ...
Most experts agree that current techniques for assessing cancer risk cannot generate a single precise estimate of human risk and that risks may best be expressed in terms of ranges or confidence intervals. One way of ensuring that such estimates are not overinterpreted is to state the assumptions underlying specific assessments and to discuss the uncertainties surrounding the numerical estimates, including both point estimates and upper confidence limits for all extrapolation models.
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From page 10... ...
For each compound, the committee reviewed all available data on metabolism, health effects in humans and laboratory animals, mutagenicity, carcinogenicity, and teratogenicity. Cancer risk was estimated for several substances, and when data were adequate, the committee also developed risk assessments for noncancer health effects.
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