Per- and polyfluoroalkyl substances in dog blood serum levels and semen quality

Growing evidence links chemical exposure to declining reproductive function in both humans and dogs. Our aim was to investigate the exposure of a wide range of per- and polyfluoroalkyl substances (PFAS) in dog serum and to investigate the association between PFAS exposure and endocrine parameters as well as semen quality.

Semen samples (n=65) were collected from Bernese mountain dogs during 2020. Sperm motility was evaluated under a phase-contrast microscope (100×, 200×). Total sperm count was calculated using a Bürker chamber. Sperm morphology was evaluated using standard protocols in wet preparations of semen fixed in buffered formalin and stained with carbolfuchsin-eosin. Serum was analyzed using a combined targeted and suspect screening approach for quantitative analysis of 50 PFAS. Following extraction, instrumental analysis was performed using an ultra-high-performance liquid chromatograph coupled to a Q ExactiveOrbitrap mass spectrometer. PFAS concentrations were associated with semen quality and endocrine biomarkers using Least Absolute Shrinkage and Selection Operator (LASSO) regression.

In all samples, PFOA, PFNA, PDFA, PFPeS, PFHxS and PFOS could be detected, although PFPeS levels were not above the quantification limit. The levels of the dominant congeners were on average (5^th-95^th percentile) PFOA 0.44 (0.05-1.3) ng/g serum, PFHxS 0.39 (0.05-0.96) ng/g serum, and PFOS 2.1 (0.35-6.4) ng/g serum. Fifteen suspect PFAS congeners were identified, where perflouro-4-ethylcyclohexanesulfonate (PFECHS), H-PFOA, H-PFNA, and H-PFDA were found in > 60% of the samples. Significant associations were found between PFBS motility (β = 136.56, p = 0.03) and free androgen index (β = 0,931, p=0.02).

For the first time, levels of a wide range of target and suspect PFAS are described in dog serum. PFAS levels in dog serum were similar to those in cats and humans, confirming that humans and pets, to a considerable extent, may share exposure to PFAS through the home environment. The study contributes to bridging the existing knowledge gap of exposure to endocrine disruptors and health effects in dogs, and thus to the research infrastructure bridging between species with the benefit of both humans and pets in a true One Health approach.