PFAS in the Wild: A Field Study on Exposure and Effects of PFAS on Tree Swallows
Tamar Schlekat, SETAC Global Science Affairs Director
It is widely recognized that per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals,” have become a global environmental contaminant. Like many pollutants, PFAS enter ecosystems through identifiable sources (point sources), such as manufacturing plant discharges or areas where PFAS-containing fire suppressants have been used. They can also originate from diffuse, harder-to-trace sources (non-point sources), including wastewater treatment plants that aggregate residual from consumer products, such as stain-resistant fabrics, nonstick cookware and utensils, and food packaging.
PFAS have been detected in soil, water, plants, animals and humans across all continents. Despite their widespread presence, many of their ecological effects remain poorly understood. While numerous laboratory studies have investigated PFAS exposure in various species, data on impacts in wild populations are much more limited. Field studies, which could fill this gap, are relatively rare due to the significant time and financial resources they require.
In a recent study, “Tree swallows as Indicators of Per- and Polyfluoroalkyl Substance (PFAS) Exposure and Effects at Selected Department of Defense Sites along the East Coast and at Sites with Other PFAS Sources in the Upper Midwest, USA” published in Environmental Toxicology and Chemistry, Christine M. Custer from the U.S. Geological Survey and her co-authors examined PFAS levels in the tissues and diet of tree swallows at sites with differing PFAS contamination histories. They also assessed how exposure affected the birds’ reproductive success.
Tree swallows, cavity-nesting migratory birds native to the Americas, were selected as the study species due to their established role in ecotoxicological research. These birds are easily attracted to specific habitats via nest boxes, and their diet, which includes aquatic insects that emerge from sediment, makes them good indicators of contaminant exposure. Furthermore, a well-developed suite of physiological biomarkers exists for this species, enabling assessment of potential health impacts.
The study revealed elevated PFAS concentrations at sites where firefighting foams had been used, compared to reference sites without such contamination. Higher PFAS levels were also found near known historical sources, such as waste disposal areas linked to manufacturing or industrial facilities.
Despite these elevated exposure levels, Custer et al. did not find statistically significant associations between PFAS exposure and reproductive outcomes such as hatching or fledging success. Similarly, no significant effects were observed across a range of biomarker responses, including two immunological endpoints.
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