Per- and polyfluoroalkyl substances (PFAS) in ski products: Environmental contamination, bioaccumulation and effects in rodents

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of anthropogenic contaminants that are widespread in the environment. Due to the strong persistency and water and lipid repellency, PFAS have been used in a wide range of industrial processes and consumer products. The widespread use of PFAS leads to a continuous diffuse environmental and human exposure. PFAS have been used in fluorocarbon-based ski waxes since the 1980s and the chemical composition is continuously evolving. When the skis are being used, the wax will abrade from the ski sole, and be distributed in the environment. This can potentially lead to PFAS hot spots near ski resorts and ski tracks.

The aim of the current thesis was to investigate the environmental and biota occurrence, distribution, and toxicological effects of PFAS from ski products, studying a local environment and rodents near a ski arena. Soil-, earthworm- (Eisenia fetida) and bank vole (Myodes glareolus) samples were collected from a Norwegian skiing area (Granåsen, Trondheim, Norway) and from a reference area with no skiing activities (Jonsvatnet, Trondheim, Norway). PFAS concentrations and composition (referred to as PFAS profile) were analyzed and compared with previous studies on commercial fluorinated ski waxes. Possible PFAS-related effects on the dopaminergic and steroid hormone systems and relative liver weight (hepatosomatic index; HSI) in the wild bank voles were also investigated. These results were further reproduced in a controlled laboratory exposure study using A/J mice (Mus musculus).

The summarized PFAS concentrations (∑PFAS) were significantly higher in bank voles from the skiing area compared to the reference area, and 35% higher in earthworms from the skiing area, compared to the reference area. The PFAS profile in samples from the skiing area resembled that of the previously analyzed commercial ski waxes, dominated by long-chained PFAS, while the samples from the reference area were dominated by short-chained PFAS. This indicates that animals inhabiting skiing areas are exposed to higher PFAS concentrations than animals inhabiting areas with no skiing activities, and that these PFAS most likely are derived from fluorinated ski wax.

Significant effects on the dopaminergic system were detected in both the bank voles from the field and the A/J mice exposed in the laboratory. However, the observed effects on dopamine (DA) concentrations were contradictory in the two studies, suggesting that potentially different molecular mechanisms could be affected. The bank voles from the skiing area had significantly higher brain DA concentrations, compared to the reference area. There was a negative association between PFAS and transcription level of monoamine oxidase (mao), encoding the Mao enzyme which is important for DA-metabolism. Thus, PFAS may have reduced the levels of Mao enzymes, leading to lower DA metabolism and thus a build-up of DA in the brain. The PFAS exposed male A/J mice, however, had significantly lower DA concentrations in their brain, compared to control mice, with parallel lower transcription levels of tyrosine hydroxylase (th), which encodes an enzyme that is important for DA synthesis. Thus, PFAS may have reduced the levels of Th enzymes, resulting in lower synthesis of DA and thus decreased DA concentrations in the brain.

Alterations of the dopaminergic system in small mammals can lead to cognitive disturbances and may affect the modulation of fear and anxiety, thermoregulation processes, defense responses and reproductive pathways. Excessive or deficient levels of DA have been hypothesized to contribute to a broad spectrum of mood, motor, and thought abnormalities. Thus, the possible PFAS-related alterations of the dopaminergic system and associated signaling pathways might potentially produce neurological disfunctions that may affect individual fitness of the exposed rodents.

Reduced testosterone (T) concentrations were detected in the muscle tissue of male bank voles from the skiing area, compared to the reference area. In the A/J mice, however, there were no effects of PFAS exposure on T, 17b-estradiol (E2) or 11-Ketostestosterone (11-KT) concentrations in either muscle- or plasma samples. The fact that there was no effect on the steroid-hormone system of A/J mice suggests that the observed associations between T and PFAS in the field study could potentially be due to other, non-measured variables in the nature, rather than PFAS alone. However, this discrepancy could also be caused by a range of other differences between the field and laboratory conditions, including different species, age or interactions with other pollutants and/or stressors.

In the A/J mice, the HSI was significantly higher in exposed males, compared to control males. In the bank voles, however, there was no difference in HSI between the skiing area and reference area. This indicates that the PFAS mixture that is based on the composition of fluorinated ski waxes could potentially produce toxicological and/or physiological responses in the liver, but it does not appear to increase the liver weight at the concentrations, or conditions that the wild bank voles were exposed to in the current study.

The liver PFAS concentrations reported in the bank voles from the skiing area and PFAS-exposed A/J mice, were within the range of concentrations reported in the plasma of professional waxing technicians. This indicates that the effects observed on the dopaminergic and endocrine systems in rodents could possibly be of concern for humans that are exposed to PFAS from ski wax products, although species-specific differences in toxicokinetics and toxicodynamics should be considered. The results presented in this thesis should be used to inspire future research on mixture effects of PFAS, preferably at environmentally- or human relevant concentrations, on the liver weight and the complex dopaminergic and steroid hormone systems.