Toxicologic Assessment of the Army's Zinc Cadmium Sulfide Dispersion Tests (1997) / Chapter Skim
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Scientific Feasibility of Epidemiologic Study
Scientific Feasibility of Epidemiologic Study
Pages 82-93
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From page 82... ...
The second discusses key methodologic issues that need to be considered in deciding whether an epidemiologic study is feasible and likely to produce scientifically valid information about a particular exposure and health outcome. The last section discusses the types of epidemiologic studies that were considered by the subcommittee in light of available information, including that provided by members of the public at public hearings.
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From page 83... ...
An individual's risk of disease cannot be determined through epidemiologic study; rather, such study determines average risks for populations or at least for representative samples. In general, epidemiologic studies are designed to study risk factors for a specific disease or the possible health elects associated with a specific exposure.
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From page 84... ...
These issues are discussed below as they relate to a possible study of health effects of exposure to ZnCdS. ~ Is a welI-definedpopuiation comprising clearly defined exposed and unexposed indhividuals availablefor study?
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From page 85... ...
A second limitation of the exposure data involves the inability to distinguish between cadmium from the Army's tests and cadmium derived from other sources. If the exposure of interest for determining health effects is exposure to cadmium, the exposure to cadmium from ZnCdS would be very low and indistinguishable from background environmental and industr~al sources of cadmium (see Chapter 5~.
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From page 86... ...
Several characteristics will determine whether exposed people exhibit disease, such as age, genetic predisposition, immune function, and health status. In addition to dose, the duration and timing of the exposure might affect the magnitude and severity of human health effects, as discussed below.
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From page 87... ...
A review of the scientific literature suggests that only a few health outcomes Knight be linked to cadmium exposure: lung cancer, dysfunction of the proximal renal tubules, and possibly infertility and low birth weight. The spectrum of health effects reported in the subcommittee's public hearings is much wider" infertility, mental retardation, autoimmune disease, melanoma, lymphoma, leukemia, chronic lung disease, breast cancer, joint pain, skin problems, and many others.
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From page 88... ...
Statistical power is the ability to detect a true difference in health status, given the size of a population, the prevalence of exposure, and the expected size of the elect. We specifically chose those 2 health outcomes on the basis of scientific evidence and public concern.
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From page 89... ...
Those limitations, coupled with difficulties in identifying exposed and unexposed populations other than by crude estimates based on residence, argue against an epidemiologic study. TYPES O F EPI D EM IO LOG IC STU D I ES The subcommittee considered several epidemiologic approaches in determining the feasibility of conducting an epidemiologic study of the health effects from ZnCdS exposure.
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From page 90... ...
and lack of information on other exposures that could cause the diseases being studied. For other nonfatal health outcomes, there are no standardized reporting mechanisms in place that would parrot a scientific analysis.
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From page 91... ...
Although current health status could be determined for some, an epidemiologic study would not be able to determine scientifically whether ZnCdS exposure caused a disease, given the absence of reliable information on exposure, individual dose, or other potential confounders. Small increases in cadmium exposure or cancer risk attributable to cadmium Dom ZnCdS exposure would be indistinguishable from those related to background sources of cadmium and other risk factors for cancer.
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From page 92... ...
Although lung cancer and kidney disease have been linked to occupational cadmium exposure, no known health effects have been associated with ZnCdS. Exposures (to cadmium from ZnCdS in a worse-case scenario)
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From page 93... ...
Information on potential confounders also would be lacking. The subcommittee concludes that an epidemiologic study of the affected populations is not feasible.
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