Because the regulations for pathogen control are technologically based rather than risk based, it is important to verify that the technology is achieving the intended results. Such verification includes a review of the management practices required for Class B land application, because they are predicated on the assumption that further pathogen reduction is achieved through the implementation of such practices.
The right side of the figure shows the points in the process where human exposures can occur and, by implication, the different populations and circumstances that might be involved. Although routine human health surveillance is unnecessary and impractical because of the wide variety of possible outcomes, the committee believes that specific circumstances might afford opportunities for health effects studies, such as epidemiological studies of occupational groups or investigations arising from reports of disease outbreaks plausibly connected to biosolids exposure.
Ideally, risk assessment of biosolids should be based on complex-mixture data to include risks from chemicals and pathogens. However, that type of data is not available in either sufficient quantity or quality (see Chapter 3), and methods have not been developed for integrating and characterizing the range of risks that might occur from exposure to mixtures of chemicals and pathogens. Thus, it remains necessary to use a component-based approach to assess risks from pathogens and chemicals in biosolids. The committee found that although the chemical-specific risk assessments conducted to establish the Part 503 regulations can be improved by using new risk-assessment methodology, the remaining uncertainty for complex mixtures of chemical and biological agents is sufficient to preclude the development of risk-management procedures that can reliably result in acceptable levels of risk. Some form of treatment-process quality assurance and ongoing surveillance must be done to ensure that effects not anticipated by the agent-specific risk assessments do not occur.
Figure 7–1 should be used by EPA as a framework for managing the risks from exposure to biosolids. The framework includes audits of treatment-process performance and management practices, periodic hazard surveillance, and studies of health outcomes, including preplanned studies and studies in response to episodic events. For example, as recommended in Chapters 2 and 6, surveys should be conducted to verify that Class A and Class B treatment processes perform as assumed by engineering principles, and determinations of