Per- and Polyfluoroalkyl Substance (PFAS) Levels in Drinking Water and Their Association with Cancer in Canines: Implications of Canines as Human Sentinels

Per- and polyfluoroalkyl substances (PFAS), known as “forever chemicals” are a range of widely used, human-synthesized chemical compounds applied in numerous capacities across the globe including food packaging, firefighting, and manufacturing products with non-stick or water-resistant properties. PFAS exposure from point-source occupational and industrial contamination has been linked to several types of human cancers including kidney, thyroid, hematopoietic, and reproductive system organs. Because companion canines typically share the same environmental exposure as their human owners or companions and are prone to similar diseases, often with a shorter latency period, they are considered an ideal sentinel for observing environmental health risks to humans. In this cross-sectional study, we examined whether elevated levels of two types of PFAS present in U.S. public water systems–Perfluorooctanoic acid (PFOA) and/or Perfluorooctane sulfonate (PFOS) levels–were associated with lifetime cancer prevalence in companion canines assessed from June 2022 to June 2023. We linked geocoded canine residence information from the 2022 Dog Aging Project (DAP) Curated Data Release with geocoded PFOA and PFOS levels recorded in the U.S. Environmental Protection Agency (EPA) Unregulated Contaminant Monitoring Rule 5 (UCMR 5) dataset. to investigate whether PFOA and/or PFOS exposure exceeding the EPA proposed action level of 4.0 parts per trillion (ppt) was associated with select cancer outcomes in companion canines that have been linked to human PFAS exposure: kidney, thyroid, and hematopoietic cancer. Due to small case counts for kidney and thyroid cancers in the DAP data, we also analyzed two other prevalent cancer types in the combined dataset: mast cell and muscle and soft tissue cancers (MSTC). Our secondary aim investigated whether canine cancer prevalence was lower in states that elected to implement PFAS maximum contaminant level (MCL) policies prior to the April 2024 EPA federal mandate. Prevalence ratios (PR) and 95% confidence intervals (CI) estimated from Poisson regression models adjusted for age, canine size, and neighborhood-level socioeconomic disadvantage status did not indicate evidence of positive associations between elevated PFOA and/or PFOS exposure and any of the cancer types investigated: hematopoietic cancer (PR = 0.44, 95% CI: 0.10, 1.86), mast cell cancer (PR = 1.23, 95% CI: 0.70, 2.17), and MSTC (PR = 0.84, 95% CI: 0.45, 1.56). For the secondary aim, PRs and Cis estimated from Poisson regression models adjusted for neighborhood-level particulate matter 2.5 similarly did not find evidence of positive associations between state PFAS MCL policy and the cancer outcomes we investigated: kidney cancer (PR = 0.61, 95% CI: 0.13, 2.94), hematopoietic cancer (PR = 0.54, 95% CI: 0.20, 1.44), mast cell cancer (PR = 1.19, 95% CI: 0.75, 1.90), MSTC (PR = 0.78, 95% CI: 0.47, 1.29). Together, these findings cannot be taken as evidence of clear protective or harmful effects of PFOA and/or PFOS exposure but rather the need for future research into the impacts of these chemicals and PFAS MCL policies on cancer in canine and human populations.