A groundbreaking new study published in Environmental Toxicology and Chemistry, a prestigious journal managed by Oxford University Press, unveils alarming evidence of widespread contamination of “forever chemicals” in various populations of tree swallows across the United States. These findings shine a spotlight on the pervasive environmental presence of per- and polyfluoroalkyl substances (PFAS) and raise critical questions about their ecological impact. Despite the high levels of exposure identified, the study reports no statistically significant effect on the reproductive health of these migratory birds, adding a complex layer to our understanding of chemical pollutants and their ecological consequences.
PFAS, colloquially known as “forever chemicals,” have become emblematic of modern chemical pollution due to their extraordinary persistence in the environment. Engineered for their resistance to heat, water, and oil, these synthetic compounds are omnipresent contaminants emanating from diverse sources such as industrial discharges, firefighting foams used at military bases, and effluent from wastewater treatment plants. Given their inclusion in a myriad of consumer products—ranging from stain-resistant textiles to nonstick cookware and food packaging—PFAS have infiltrated ecosystems worldwide, accumulating in soil, water bodies, flora, fauna, and even human populations, raising urgent concerns about their long-term ecological and health impacts.
The resilience of PFAS molecules arises from the strong carbon-fluorine bonds that make them remarkably resistant to biodegradation and chemical breakdown. This durability results in persistent bioconcentration in organisms and bioaccumulation through food webs, posing potential chronic exposure risks to wildlife and humans alike. Although extensive laboratory research has linked PFAS to a variety of adverse health effects, including carcinogenicity and reproductive disorders in animals, there remains a crucial dearth of knowledge regarding their effects in natural, free-ranging populations. Field research capable of resolving these knowledge gaps is notoriously challenging due to the extensive timeframes, comprehensive sampling, and the financial resources required.
Addressing this critical void, the current investigation employed an observational study design to measure PFAS concentrations in both tissues and dietary sources of tree swallows (Tachycineta bicolor), a widely distributed North American migratory bird species. Researchers strategically selected sites with varied contamination histories across several Department of Defense installations and other environments, facilitating a thorough comparison of PFAS exposure gradients. These sites include locales such as Willow Grove, Pennsylvania; Lakehurst, New Jersey; Camp Springs and Chesapeake Beach in Maryland; Ashumet Pond in Massachusetts; and multiple locations in Minnesota and Illinois, including the urban-adjacent Cottage Grove site near Minneapolis/St. Paul.
Analysis revealed markedly elevated PFAS concentrations at sites with histories of firefighting foam application and in proximity to urban centers, corroborating the impact of anthropogenic chemical releases. Notably, the compound perfluorohexane sulfonate (PFHxS) was found in exceptional concentrations near Cottage Grove, a contamination hotspot influenced by residues from local manufacturing plants and various industrial and household sources from the broader metropolitan area. This discovery underscores the heterogenous nature of PFAS pollution, emphasizing the mixture of legacy contamination and ongoing urban-derived inputs in shaping exposure profiles.
Intriguingly, despite substantial inter-site variability in PFAS levels among tree swallow populations, the comprehensive reproductive assessments yielded an unexpected conclusion: PFAS exposure did not demonstrably impair key reproductive metrics. Parameters including hatching success and fledgling viability showed no statistically significant correlation with chemical burden, suggesting a surprising level of resilience or tolerance in these avian populations. The chicks’ physical development, including their ability to grow and develop flight competence, appeared unaffected by the contamination, a finding that contrasts with existing laboratory evidence on PFAS toxicity and warrants further mechanistic exploration.
This research challenges prevailing assumptions about the ecological ramifications of PFAS exposure, emphasizing the complexity of translating laboratory toxicity data to wildlife field scenarios. The absence of apparent reproductive detriments might result from adaptive physiological mechanisms in tree swallows, species-specific pharmacokinetics of PFAS, or other environmental variables influencing toxicity outcomes. The study also underscores the importance of field-based ecological research to fully delineate the real-world implications of persistent environmental pollutants, which are often obfuscated by laboratory-based extrapolations.
Moreover, the multidimensional approach—combining chemical assays in tissues and diet with detailed reproductive performance data—provides a comprehensive framework that other ecotoxicologists can emulate. By focusing on an ecologically relevant sentinel species, this research contributes significantly to the discourse on bioindicator selection for monitoring emerging contaminants. The migratory behavior and insectivorous diet of tree swallows make them ideal candidates for assessing PFAS dissemination across diverse ecological landscapes, highlighting the interconnectedness of urban, industrial, and natural ecosystems.
The implications of this study extend to environmental policy and management, particularly regarding the oversight of PFAS contamination originating from both legacy military sites and contemporary urban environments. The findings invite a reconsideration of ecological risk assessment paradigms, pressing for refined models that integrate species-specific responses and field conditions. Additionally, the persistence and ubiquity of PFAS continue to evoke concerns about cumulative ecosystem impacts and potential long-term effects that may not manifest within the timeframe of this study.
Publication of this landmark paper, titled “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,” was set for release on October 8th, 2025. This work represents a collaborative endeavor funded by the Strategic Environmental Research and Development Program, the U.S. Department of Defense, and the U.S. Geological Survey, highlighting the cross-agency interest in addressing PFAS contamination and its multifaceted challenges.
Correspondence regarding this research may be directed to Christine M. Custer of the U.S. Geological Survey’s Upper Midwest Environmental Sciences Center in La Crosse, Wisconsin. The study is accessible online via the DOI: 10.1093/etojnl/vgaf207. For media inquiries or to request a copy of the publication, contact Daniel Luzer at Oxford University Press.
The burgeoning evidence of PFAS contamination in critical wildlife populations exemplifies the escalating environmental dilemma posed by synthetic chemical pollutants of remarkable persistence. While this study refrains from linking detectable biological impacts on tree swell reproductive health, it importantly signals the necessity for sustained monitoring and rigorous investigation into the subtle, long-term ecological effects of these enigmatic chemicals. As research progresses, tree swallows may well serve as sentinels—illuminating the silent, pervasive presence of forever chemicals in our ecosystems and guiding informed actions toward environmental stewardship.
Subject of Research: Animals
Article Title: 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
News Publication Date: 8-Oct-2025
Web References:
https://doi.org/10.1093/etojnl/vgaf207
Keywords:
Ecosystems, Behavioral ecology, Ecological dynamics, Ecological risks, Species interaction, Reproductive biology
