A wastewater balance reveals unexpectedly high TFA input from human water use

Trifluoroacetate (TFA) is a member of the PFAS group and shares their persistence. Its very small molecular size and anionic character makes it, in contrast to many other PFAS, highly water-soluble and mobile in the aquatic environment. Wastewater shows elevated TFA concentrations. This TFA may stem from background sources such as drinking water, infiltrating groundwater, or rainwater. It may also come from human water use itself. To quantify a potential TFA surplus, we built a mass balance at three rural sewer sites in Freiburg, Germany. End-member mixing analysis yielded TFA loads from groundwater and drinking water. Flow comparisons between dry and rain-event conditions yielded the TFA load from rainwater. Groundwater and drinking water contributed the largest background TFA load at two sanitary sewers. During a storm event rainwater dominated the TFA load in the combined sewer despite diluting its concentration. At every site, human water use exceeded the sum of the three background sources and made up the largest share of the TFA load. TFA concentrations also peaked during the morning wastewater surge at every site. We attribute this surplus mainly to human excretion of ingested TFA from food and drink. However, a comparison with an approximate dietary TFA intake estimate shows that this source alone cannot explain the observed surplus. Other sources, such as cosmetic products, may contribute to the overall TFA load in the sewer. Our study highlights the need for more data on human TFA uptake and excretion, as well as on other potential sources of TFA in human water use.