Biosolids in Washington State: Putting per- and poly-fluorinated alkyl substances concerns into a real-world context

Washington State has a history of beneficial use of municipal biosolids. The Department of Ecology recently conducted a voluntary survey of per- and poly-fluorinated alkyl substances (PFAS) in biosolids. Results of that survey are presented and compared with the results from mandatory sampling in Michigan. For the majority of the utilities that participated, residential flow was found to be the primary source of PFAS for biosolids suggesting that industrial source control will not limit their presence in biosolids. Distribution of PFAS was similar to that identified in the Michigan sampling. The results of the sampling were put into the context of current biosolids end use to evaluate the potential for increased human exposure to PFAS as a consequence of beneficial use of biosolids. This was done in the context of identifying the potential for a highly exposed individual (HEI) as is traditionally done in risk assessment and was recently done in a draft Environmental Protection Agency risk assessment. The majority of end use sites; dryland wheat and commercial tree plantations, show no realistic potential for a HEI. Others, such as garden vegetables and animal feed crops, have identified exposure pathways and may merit additional sampling.