biosolids go beyond the wastewater treatment plant to other worker populations, such as appliers and farmers, and to the general public, such as communities living near land-application sites and consumers of crops grown on biosolids-amended soils. Exposed populations may also include sensitive subpopulations, such as children, immunocompromised individuals, and the elderly, who are unlikely to be prevalent in the workplace.

Findings: There is a lack of exposure and health information on populations exposed to biosolids. Therefore, although the land application of biosolids has occurred for many years with little, if any, systematic documented evidence of adverse effects, there is a need to gather epidemiological data and to investigate allegations of health incidents. EPA needs to study more rigorously the exposure and health risks, or the lack thereof, in worker and community populations exposed to biosolids.

Recommendations: Although routine human health surveillance of all populations exposed to biosolids is impractical, the committee recommends that EPA promote and support response investigations, targeted exposure surveillance studies, and a few well-designed epidemiological investigations of exposed populations. This recommendation is intended to provide a means of documenting whether health effects exist that can be linked to biosolids exposure. The committee recommends the following types of studies:

  • Studies in response to unusual exposures and unusual occurrences of disease. Occasionally, the occurrence of unusual events can provide information on the agents of disease. For example, an outbreak or a symptom of disease might occur following a known exposure or an unusual exposure scenario. In both instances, exposure and health outcomes should be determined.

  • Preplanned exposure-assessment studies. Such studies should characterize the exposures of workers, such as biosolids appliers and farmers, and the general public who come into contact with constituents of biosolids either directly or indirectly. The studies would require identification of microorganisms and chemicals to be measured, selection of measurement methods for field samples, and collection of adequate samples in appropriate scenarios. A possible exposure-assessment study would be to measure endotoxin exposure of workers at biosolids production and application sites and of communities nearby.

  • Complete epidemiological studies of biosolids use. These studies should be conducted to provide evidence of a causal association, or a lack thereof, between biosolids exposure and adverse human health effects. They should include an assessment of the occurrence of disease and an assessment or measurement of potential exposures. An example of a longitudinal epidemio-

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