Dr. Doug Cox is a Senior Toxicologist and Environmental Risk Assessor in GHD's Golden Colorado office. He has a Ph.D. and M.S. in Pharmacology and Toxicology and is a full member of the Society of Toxicology. Doug has extensive experience developing toxicology evaluations, human health and ecological risk assessments, as well as risk management and risk communication strategy. He is part of GHD’s PFAS Initiative, a market area of increasing public and regulatory concern due to widespread soil and groundwater contamination.
The Impacts of Compounding Uncertainties on Evaluating Risk from Perfluorinated Alkyl Substances (PFAS) Compounds
Complexity and uncertainty are part of every facet of a PFAS site investigation and risk assessment. Using PFAS case studies from Australia and the United States as examples, this presentation discusses the compounding effects of multiple uncertainties and describes how GHD has managed them. Too often the approach to managing uncertainty is to include additional safety factors, which can dramatically increase the effort and perceived risk at a site. By understanding how these uncertainties affect the site investigation process, GHD has developed approaches to limit their significance and impact. Current treatment options to address PFAS are limited in scope and scale, and understanding the uncertainties is critical for making informed mitigation and remediation decisions. Careful program management is required to avoid letting uncertainties dominate the process. For example, during data collection, samplers have to follow specific precautions to avoid cross-contamination from clothes, notebooks, and field equipment. Laboratories are faced with requirements for extremely low detection limits, yet methods for measuring PFAS in many media have not been approved. Additionally, labs lack standards for many individual chemicals, and analytical results from different methods can yield results that are hard to reconcile. For toxicologists, there are sufficient data to estimate risk for only a handful of compounds, yet labs generate analytical results for several dozen, many of which cannot currently be evaluated for risk. Humans eliminate PFAS at different rates than experimental animals, and pharmacokinetic models have been developed to normalize body burden and elimination rates between animals and humans. The toxicological mechanism of action has not been well defined, and a variety of unrelated effects have been observed in the liver, immune system, reproduction and development, and blood cholesterol. Exposure assessment is confounded by background levels of PFAS in numerous commercial and industrial products. PFAS in milk has been attributed to using biosolids as fertilizers on farm fields, and PFAS has been measured in wild fish and game. Currently the exposure scenario getting the most attention is the drinking water pathway, but risks from other exposures have not been well defined. The bioaccumulative nature of PFAS leads to long-term concerns as well. Finally, regulators are facing challenges as to how to assess and manage PFAS risks and wastes. EPA has not listed them as hazardous substances and a federal MCL has not been developed. State health agencies are adopting their own criteria, which are lower than EPA’s advisory levels. National and multi-state companies are facing challenges in managing their liabilities across multiple jurisdictions. When combined, these uncertainties can have a compounding effect Given the extensive but not always accurate media coverage, these uncertainties are not easily communicated to stakeholders, and have contributed to a high level of anxiety regarding PFAS risk This has also driven reactionary response measures that in some situations are not technically or economically feasible, and result in minimal overall benefits when implemented. Understanding, appreciating, and effectively communicating uncertainties can go a long way towards developing a suitable response based on actual risk.