National Academy of Sciences. Biosolids Applied to Land:
Advancing Standards and Practices

Chapter 3: Epidemiological Evidence of Health Effects Associated with Biosolids Production and Application [abridged]

This chapter reviews the epidemiological literature concerning workers and community residents potentially exposed to biosolids during production and application. This literature is valuable for four reasons: (1) it may provide documentation of human-health consequences of exposure to biosolids under the circumstances of their production, application, and use; (2) it may provide information on routes of exposure, such as airborne transmission or ingestion; (3) it may provide information on a dose-response relationship; and (4) it may identify gaps in the literature. Recognition of gaps is essential to distinguish between no evidence of effect and evidence of no effect. Finally, even though all prediction is based on logical extension from available information, an epidemiological review can provide an assessment of the strength of the knowledge foundation from which predictions are made.

The committee was apprised of various human-health allegations associated with biosolids exposure from news articles, written submissions from the public, and citizens who attended its public meetings. It was beyond the committee's charge to investigate or verify these allegations. Thus, the committee limited review to studies published in the peer-reviewed literature and reports from government agencies. The review included studies that investigated health effects or provided biomonitoring data (evidence of biological absorption [i.e., chemical absorption into the body]) and excluded studies limited to human exposure without evidence of biological absorption or human health effects. Although the committee was asked to focus on public health, the review includes epidemiological studies involving production and application 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.

NOTE: THE BULK OF CHAPTER 3's MATERIAL IS NOT INCLUDED, JUST THE FOLLOWING FINDINGS AND RECOMMENDATIONS

FINDINGS AND RECOMMENDATIONS

Finding: The committee concludes that because of the lack of epidemiological study and the need to address the public's concerns about potential adverse health effects, EPA should conduct studies that examine exposure and potential health risks to worker and community populations. Studies of wastewater treatment workers should not be used as substitutes for studies of actual biosolids exposure. While routine human health surveillance of all populations exposed to biosolids is impractical, the committee recommends that EPA promote and support a research effort to reduce uncertainty about the possible health consequences of exposure to biosolids. Stakeholders should be involved in review of the design, conduct, and interpretation of studies

The committee recommends the following types of study.

Response Studies

Studies in response to unusual exposure and unusual occurrence of disease. On occasion, unplanned events occur that can provide information on the agents of disease. An example might be an outbreak or a symptom of disease following a known exposure or an unusual exposure scenario. In both instances, exposure and health outcomes should be determined.

Preplanned Studies

Biosolids 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 routine 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 epidemiological study would be an evaluation of health effects in a cohort of biosolids appliers; these workers should be characterized by duration and level of exposure, with appropriate follow-up.