Formatted Title
Contribution of Home-Produced Food Pathways to Potential Exposure Pathways for Perfluoroalkyl Substances (PFAS) in Residential Soils
Background/Objectives
Regulatory cleanup standards, such as the USEPA Regional Screening Levels (RSLs), are derived under the assumption that direct contact pathways to soils, such as incidental ingestion, dermal contact and inhalation of particulates, comprise the pathways with the highest potential contribution to exposure and risks. Exposure from ingestion of home-produced foods can also present a complete exposure pathway and for bioaccumulative compounds, may contribute more to the overall dose than the direct soil contact pathways. Some jurisdictions include a generic adjustment factor (i.e., relative source contribution term) that is based on the assumption that non-contact pathways, such as the growing and consuming home-produced foods, may contribute a percentage as high as 80% to 99% of the total exposure.
Approach/Activities
In this presentation, two noncontact exposure pathways to soil, the consumption of the home-produced garden produce and backyard chickens (both meat and eggs), are evaluated in concert with the direct contact pathways from soil to estimate exposure pathways that have the highest contribution to the total average daily dose (ADD) and/or drive down risk-based criteria. This research evaluated two PFAS, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), using available literature data to determine the potential contribution of these pathways for an example resident receptor from whom both direct and indirect contact are complete. This evaluation utilized standard USEPA risk assessment guidance and toxicity values as well as literature-based estimates for uptake into the edible portions of both produce and backyard chickens (both meat and eggs).
Results/Lessons Learned
Based on these metrics, PFOA in residential soils is estimated to contribute more than 90% of the ADD from the consumption of home-produced chicken eggs. Conversely, for PFOS, the consumption of garden produce (both fruit and vegetables) would have a similar contribution to the ADD for a resident. Also provided are analyses and probability distributions of the data and limitations for these pathways and a discussion of the need for additional studies (e.g., impacts to these pathways from groundwater) to address key sources of uncertainty in human health risk assessments and deriving protective risk-based cleanup criteria.