of biosolids by workers, in addition to assessments of health effects in community residents. The rationale for inclusion of information on worker exposure is that occupational exposure, which for many toxicants is usually higher in exposed workers than in residents exposed from the general environment, often provides a substantial basis for extrapolating risk assessment from higher occupational concentrations to lower environmental concentrations.
The committee also considered potential risks from odors and disease vectors, but did not find any epidemiological studies of these types of risks related to biosolids. Odors and disease vectors have often been categorized as nuisance or aesthetic issues, but odors can have adverse physiological and psychological effects (see Chapter 5) and vectors can transmit disease (see Chapter 6). These are issues that need careful consideration, as there appears to be a fine line between when odors or disease vectors are merely nuisance issues and when they are health issues.
The committee evaluated 23 studies relevant to the assessment of human health effects associated with biosolids exposure and divided them into six major focus populations: (1) biosolids users (e.g., farmers and home gardeners), (2) populations near agricultural application sites, (3) workers involved in biosolids production and application, (4) populations near sewage treatment plants, (5) workers in sewage treatment plants, and (6) compost workers. Few epidemiological studies were conducted specifically for biosolids exposure. There are substantially more studies of workers in sewage treatment plants and populations living near them. Although those studies do not involve exposure to biosolids per se, they were included because they provide valuable information about hazards to sewer workers and others exposed to raw sewage that could be used to identify potential hazards from biosolids. However, an exhaustive review of the literature on exposures from sewage treatment plants was not conducted.
Table 3–1 provides the details of the studies that the committee evaluated. A summary of the populations studied, the observed outcomes, and the committee’s assessment is provided below.
Biosolids users. One study documents chemical exposure from avocational gardening use of biosolids (Baker et al. 1980). This single investi-