Animals as Sentinels of Environmental Health Hazards (1991) / Chapter Skim
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6. Animal Sentinels in Risk Assessment
6. Animal Sentinels in Risk Assessment
Pages 103-120
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From page 103... ...
Those characteristics of animal sentinel studies offer important advantages over laboratory animal studies, in which animals are usually exposed to high, constant doses of a single chemical substance that is under investigation. Thus, the use of animal sentinels constitutes an approach to identifying hazards and estimating 103
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From page 104... ...
Risk assessment and risk management were distinguished and defined as follows by a previous NRC committee (NRC, 1983~: · Risk assessment: "The characterization of the potential adverse health effects of human exposures to environmental hazards." · Risk management: "The process of evaluating alternative regulatory actions and selecting among them." The same committee divided risk assessment into four components and defined them as follows: · Hazard identification: "The process of determining whether exposure to an agent can cause an increase in the incidence of a health condition.. · Dose-response assessment: "The process of characterizing the relation between the dose of an agent administered or received and the incidence of an adverse health effect in exposed populations and estimating the incidence of the effect as a function of human exposure to the agent." · Exposure assessment: "The process of measuring or estimating the intensi~, frequency, and duration of human exposures to an agent currently present in the environment or of estimating hypothetical exposures that might arise from the release of new chemicals into the environment." · Risk characterization: "The process of estimating the incidence of a
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From page 105... ...
Nevertheless, the N~C definitions are useful in clarifying the steps involved in risk assessment. This chapter discusses the role of animal sentinels and animal sentinel data in the process of risk assessment related to human health.
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From page 106... ...
In situ systems used for those purposes suffer the same drawbacks as do the systems based on wild animalsthe precision and reliability with which they track spatial and temporal variations in ambient concentrations are unknown. If such limitations could be overcome by better calibration, the systems would be very promising, at least for smald-scale applications.
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From page 107... ...
In other cases, however, blood or tissue concentrations cannot be used directly as measures of exposure- it might be necessary to derive a conversion factor, either empirically or by pharmacokinetic modeling, to obtain estimates of exposure or dose from measurements of tissue concentration. Aninais as Maims of Exposure of Their (I Animals can be used to monitor exposure most directly when the animal species sampled is used as food by the species whose exposure is to be determ~ned.
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From page 108... ...
Such studies have shown marked differences in bioavailability of TCDD in soil collected from different sites and thus illustrate a role for animal sentinels in assessing differential bioavailability. In less-controlled conditions, wild animals have been used as indicators of the bioavailability of TODD in contaminated terrestrial environments (Fanelli et al., 1980; Young and Shepard, 1982; Bonaccorsi et al., 1984; Heida et al., 1986; Lower et al., 1989~.
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From page 109... ...
Wild animals have been used widely to assess the bioavailability of metals, such as lead from soil, and hence to determine patterns of contamination and potential exposure (Williamson and Evans, 1972; Gish and Christensen, 1973; Goldsmith and Scanlon, 1977; Clark, 1979; Ash and Lee, 1980; Hutton and Goodman, 1980; Ohi et al., 1981~. Again, the results have not been used to develop quantitative estimates of human exposure, and it is not clear how they could be so used without extensive calibration exercises.
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From page 110... ...
. In only a few cases were the early warnings provided by sentinel animals distinctive and decisive enough to trigger control measures before human exposure was recognized.
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From page 111... ...
Extensive dose-response data are available on the effects of PCB-contaminated fish on reproduction in mink (Aulerich and Ringer, 1977; Hornshaw et al., 1983; Ringer, 1983~; but risk characterization for humans exposed to the same fish has been conducted by considering data on more conventional laboratory species (Swain, 1988; National Wildlife Federation, 1989; Tilson et al., 1990~. USE OF ANIMAL SENTINEL SYSTEMS IN RISK CHARAC1~;RIZAT7ON Many of the studies referred to in preceding sections of this chapter as examples of the use of animal sentinel systems in exposure assessment, hazard identification, or dose-response assessment also included applications to risk characterization.
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From page 112... ...
However, one of the principal mechanisms of toxicity inhibition by DDE of ATPase, which is responsible for membrane transport of calcium in the shell gland is known only in birds, so the information cannot be used in risk assessment for other groups of animal species. Other risk characterizations for wild animals exposed to environmental contaminants have generally been based on less-detailed information, especially on dose-response relationships.
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From page 113... ...
Thus, risks to aquatic animals exposed to concentrations at or near the AWQC are relatively poorly characterized by this procedure. Risk to Corm of Anir7tal Species trader S - y When animal sentinel systems are used to assess exposure of direct consumers of the animals that are monitored, the exposure assessments can be used directly in risk characterizations.
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From page 114... ...
. Although the studies have suggested that companion or other sentinel animals could be useful in screening for hazardous human exposures, the committee is unaware of any cases in which such systems have been used in formal risk characterizations.
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From page 115... ...
A specific advantage of animal sentinels for that purpose is that animals usually develop cancer in response to carcinogens more rapidly than do humans. Hence, in principle, identification of an excess cancer rate in sentinel animals could be used to identify risks to humans that have the same environments and to trigger remedial measures, even though the magnitude of the risks to humans could not be estimated quantitatively from the animal data.
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From page 116... ...
They include the designation of AWQCs to protect aquatic life, the prospective designation of sediment quality criteria for the same purpose (EPA, 1972) , the consideration of risks to wildlife in decisions to register or cancel pesticides, and the characterization of ecological risks as part of the process of evaluating remedial actions at uncontrolled hazardous-waste sites.
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From page 117... ...
The action levels themselves were selected to limit human risks, but in most cases involved consideration of other factors as well. Another class of regulatory actions based on consideration of risks to consumers of sentinel animals is the regulation of uses of pesticides based on residues in domestic food animals.
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From page 118... ...
Those systems use the animal sentinels both to monitor levels of environmental contamination and to detect potential effects. Although the effects are on the sentinel animals themselves, they are used as surrogate markers of potential effects on other species, including humans.
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From page 119... ...
Because of those differences, animal sentinels cannot be used quantitatively as surrogate monitors of human exposures and human responses, unless they can be calibrated against measures of human exposure or response. Calibration would require the measurement of human exposure and response in at least one case.
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