Top: Graphic courtesy Department of Ecology, Washington State

The Washington state Department of Ecology partnered with 44 wastewater treatment plants (WWTPs) statewide to conduct voluntary, one-time testing for PFAS in biosolids. The sample group included facilities of varying sizes, upstream dischargers, and regions. Ecology staff worked with plant personnel to collect and analyze biosolids samples for PFAS using EPA Method 1633, focusing on PFOS and PFOA — the PFAS compounds currently prioritized by EPA and other states. Key findings include:

• PFAS are widespread: Nearly all samples contained PFAS, regardless of facility size or location.
• Method limitations: EPA Method 1633 showed limitations when measuring PFAS in liquid biosolids, consistent with reports from other states.
• Consistent results in dewatered biosolids: Low PFAS levels were similar to findings in states without PFAS manufacturing.
• Multiple sources: Detection in both large and small facilities suggests household wastewater may contribute as much as industrial discharges.