Human Health Risk Assessment

Human Health Risk Assessment Guidance Summary

The Oregon Department of Environmental Quality published its Guidance for Conduct of Deterministic Human Health Risk Assessments in December 1998, with minor updates in May 2000. The general risk assessment concepts, based on standard U.S. Environmental Protection Agency risk assessment guidance, have not changed. However, in the past 10 years, many refinements to the risk assessment process have occurred. DEQ listed most of these changes on its environmental cleanup web page, but official updating of these changes in the actual guidance document has lagged. The October 2010 Human Health Risk Assessment Guidance updates and replaces the prior 1998 document.

Three major revisions to DEQ guidance are a result of updates to EPA guidance:

• Early-life exposure to carcinogens. Following EPA guidance, DEQ discussed evaluating early-life exposure to vinyl chloride in its 2003 Risk-Based Decision Making guidance. In the 2007 revisions to the risk-based concentration (RBC) table, DEQ expanded the table to include early-life exposure for carcinogenic polycyclic aromatic hydrocarbons (PAHs). Appendix B of DEQ’s revised Human Health Risk Assessment Guidance addresses early-life exposure for relevant chemicals.
• Inhalation risk calculations based on concentration instead of dose. EPA’s decision to evaluate inhalation exposure using concentration-based toxicity factors did not substantially alter risk assessment outcomes, although it did change the risk equations. DEQ revised the risk-based concentration spreadsheets in 2009 to reflect the new risk assessment method. Revised equations are provided in Appendix C of DEQ’s revised guidance.
• Breastfeeding as an important exposure scenario. EPA has included this exposure example in its guidance for a few years, although it is still not commonly considered. Working with EPA Region 10, DEQ found that breastfeeding is an important pathway for some bioaccumulating chemicals, particularly polychlorinated biphenyls (PCBs). The PCB non-cancer risk to an infant is generally 25 times the risk calculated for the mother. This result makes the acceptable PCB concentrations nearly equivalent for non-cancer and cancer endpoints. As a consequence, including this risk pathway on all sites will not substantially affect cleanup decisions. However, new PCB hotspot levels will be considerably lower than current levels.

  Appendix D addresses the breastfeeding exposure pathway. Including this pathway in risk assessments is important to ensure that the environment is protective of infants. However, it is critical to understand that these calculated risks are not intended to advise women about whether or not to breastfeed their infants. Rather, these listed risks are provided to inform site cleanup managers so they can make decisions that will lead to decreased exposure to women and ultimately lower concentrations of contaminants in the milk women produce for their infants. Calculated risks to infants support public health actions that encourage women to limit their own exposure to environmental contaminants so that their infants can receive the optimal health benefits from breastfeeding. Information on the important benefits of breastfeeding is available from the Oregon Office of Environmental Public Health (www.oregon.gov/DHS/ph/oeph/).

Additional revisions to the DEQ’s Human Health Risk Assessment Guidance include:

• Stating a preference for using a modified risk-based decision making process for risk assessments.
• Providing an example conceptual site model.
• Providing a revised risk assessment process flowchart and narrative starting with risk screening, and explaining when a site-specific risk assessment is warranted.
• Screening
  • Specifying use of DEQ risk-based concentrations and EPA regional screening values
  • Simplifying handling of multiple chemicals.
• Providing background levels for inorganic compounds s. (We plan to update this shortly based on a DEQ-sponsored study of background inorganic levels in Oregon.)
• Modifying exposure factors and documenting other changes.
• Adding exposure scenarios from risk-based decision making guidance for construction workers and urban residents.
• Explaining how to apply acceptable risk levels to dioxin congeners and dioxin-like PCB congeners.
• Presenting residual risk assessment process.

Implementation Schedule

DEQ will implement its revised human health risk assessment guidance according the following caveats:

1. For all newly started risk assessment at a site, the revised guidance will be used from this point on;
2. For risk assessment currently being performed, the revised guidance will be used on a case-by-case basis;
3. For completed human health risk assessments submitted before the effective date of the revised guidance, reassessments may be performed on a case-by-case basis when a new decision is required that needs to be supported by a screening evaluation or updated risk assessment. Until that time, the current completed and approved risk assessment will continue to be considered valid based on guidance used when the assessment was completed.

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