U.S. wastewater treatment fails to address rising organofluorine contamination

New research reveals that wastewater-derived organofluorine, dominated by fluorinated pharmaceuticals, threatens the safety of drinking water for millions, highlighting urgent regulatory and treatment challenges.

Study: High organofluorine concentrations in municipal wastewater affect downstream drinking water supplies for millions of Americans. Image Credit: SpiritArt / Shutterstock

In a recent article in the journal PNAS, researchers investigated the impact and presence of per- and polyfluoroalkyl substances (PFAS) in wastewater treatment facilities across the United States. Their findings indicate that treatment facilities’ highest removal efficiency of total extractable organofluorine (EOF) concentrations was lower than 25%, affecting millions of Americans’ drinking water quality.

Background

Fluorine, though abundant in the Earth’s crust, is rarely found in natural organofluorine compounds and is not vital for life. Due to fluorine’s unique properties, humans have created thousands of synthetic organofluorine chemicals since the 1940s, using them in products like refrigerants, pharmaceuticals, and nonstick coatings.

PFAS, in particular, are persistent pollutants that have been linked to adverse health and ecological effects. Pharmaceuticals that re-enter drinking water sources could affect sensitive groups such as children and pregnant people. Effects on health populations include decreased odds of pregnancy, increased risk for thyroid disease, and increased cholesterol levels. At the same time, pregnant individuals may suffer from high blood pressure or increased risks of pre-eclampsia.

Municipal wastewater treatment plants (POTWs) collect PFAS from various sources, affecting U.S. drinking water. Water scarcity has led to increased wastewater reuse, raising concerns about residual chemicals entering drinking water supplies. Researchers emphasize that risks are heightened during low-flow conditions, such as those caused by droughts, which reduce dilution of contaminants in natural waters. A national model shows that 6% of U.S. public water systems receive wastewater with minimal dilution, highlighting contamination risks.

About the Study

Existing PFAS discharge estimates often rely on manufacturing data, not direct measurements. In this study, researchers focused on quantifying organofluorine levels in wastewater, finding significant unknown compounds.

In 2021, researchers collected 24-hour composite samples from the influent and effluent of eight POTWs in the U.S., which serve over 10,000 people each. The samples were analyzed for total fluorine, fluoride, and various organofluorine compounds, including PFAS, using advanced methods like combustion ion chromatography (CIC) and mass spectrometry (LC-MS/MS and HRMS). However, the study highlights the challenges of analyzing unknown precursor compounds, which lack commercially available standards.

The samples underwent solid-phase extraction to separate organofluorine from fluoride. They analyzed 34 PFAS compounds and screened 766 small-molecule organofluorine pharmaceuticals. Total PFAS precursors were estimated using a TOP assay with Bayesian inference. The DRINCS model was employed to simulate the impact of wastewater discharges on downstream drinking water quality, linking these discharges to the number of affected people.

Findings

The analysis found that perfluoroalkyl acids (PFAA) and their precursors contribute small portions of wastewater EOF, accounting for 21% of effluents and 11% of influents. However, fluorinated pharmaceuticals dominated EOF, accounting for 62% in effluent and 75% in influent and including monofluorinated compounds such as citalopram and atorvastatin as well as polyfluorinated substances like maraviroc and celecoxib. These compounds exhibit varying degrees of environmental persistence, raising concerns about their long-term effects.

Overall, wastewater treatment proved ineffective in removing EOF, with a maximum reduction of approximately 24%. This limited efficiency is partly due to the transformation of precursors into more persistent compounds, such as PFAAs, during treatment. Researchers estimate that large wastewater treatment plants in the U.S. discharge approximately 1.7 million mol of fluorine annually. PFAS derived from wastewater may exceed limits for safe drinking water, particularly under conditions of low water flow. The study suggests that up to 23 million people could be exposed to PFAS concentrations exceeding regulatory thresholds during such conditions.

Conclusions

Regulating chemicals in the U.S. typically focuses on individual toxicants, not the complex mixtures found in wastewater, which makes managing PFAS and organofluorine compounds difficult. These chemicals, known for their persistence, lack proper analytical standards for environmental monitoring. Experts suggest a class-based regulation approach, especially for PFAS, using EOF as a preliminary screening tool. However, EOF measurements cannot distinguish among different chemical forms, requiring complementary methods to identify specific compounds.

In wastewater from large treatment plants, PFAS, especially polyfluorinated pharmaceuticals, dominate most of the EOF. Current regulations do not fully address these compounds’ environmental persistence and health risks, which are increasingly used in pharmaceuticals. Comparatively, European Union regulations cover a broader range of PFAS but have higher allowable thresholds, highlighting differing regulatory approaches. Persistent chemicals in wastewater can affect ecosystems and human health, especially sensitive populations.

Future research should focus on the environmental fate of these compounds, improve monitoring at diverse treatment facilities, and better understand their impact on ecosystems and human health. Random sampling across a wider range of facilities could offer critical insights into the variability of organofluorine contamination nationwide.

These concerning findings suggest that current wastewater treatment methods are insufficient for effectively removing EOF. Improved treatment, as well as mitigation methods at the source, are critical for managing PFAS levels in drinking water. Enhanced water treatment methods are needed to reduce people’s exposure to toxic substances in drinking water and associated health harms. Such interventions will become even more critical as climate change exacerbates water scarcity and increases reliance on wastewater reuse.