Regulatory guidance is available for evaluating site-specific bioavailability in HHRAs; Table 2-1 summarizes several key guidance documents. These documents establish a broad precedent for incorporating bioavailability values into the risk assessment process, beginning with foundational documents such as USEPA’s 1989 (USEPA 1989b) Risk Assessment Guidance for Superfund (RAGS).

Table 2‑1. Regulatory guidance

Regulatory constraints are also discussed in this guidance in the context of a site-specific decision to conduct a bioavailability assessment. The chemical-specific sections also include information about existing guidance.

In October 2015, ITRC informally surveyed risk assessors in state regulatory agencies throughout the country to understand how bioavailability is used in human health risk assessments within their jurisdiction. The following questions were asked:

• Does the state use bioavailability or relative bioavailability of contaminants in soil in risk assessments?
• If so, does the state have any guidance or policy regarding the development and application of bioavailability or RBA of contaminants in soil?

Responses were received from 14 individuals from 12 states. Additional information has been provided by state members of the BCS team for states that did not respond to the initial survey. Table 2-2 summarizes the information provided by respondents. The responses indicate that lead is the chemical for which site-specific RBA values are most often incorporated. The responses summarized in Table 2-2 should be interpreted as anecdotal experience of the individuals who responded rather than as the official position of the respective states. There also may be multiple programs within a state which have different experiences. These responses also often indicated emerging policy or precedents. The responses are included in Detailed Survey Responses.

Table 2‑2. Summary of current practices