First study of heavy metals analysis in hair and oxidative status of European Otters (Lutra lutra) from Southwestern Europe.

Heavy metal(loid)s are continuously released into semi-aquatic ecosystems. This poses a potential threat to wildlife, such as the European otter (Lutra lutra) whose population has been gradually declining. Non-invasive sampling (e.g., hair samples) offers a valuable approach to assess pollutant exposure in otters without harm. In this study, we quantified As, Cd, Hg, Pb, and Zn concentrations in the hair, liver, and kidney of European otters from NW Spain, with the aim of validating the effectiveness of hair as a non-invasive biomonitoring tool by comparing it with internal organ concentrations. The correlation between metal concentrations, age, sex, and habitat, as well as a battery of oxidative stress biomarkers (catalase, glutathione reductase, glutathione S-transferase and malondialdehyde production), were also assessed. Tissues from 28 otters were analyzed and metal concentrations were quantified by inductively coupled plasma mass spectrometry. Oxidative stress biomarkers, including antioxidant enzymes and lipid peroxidation, were determined in the liver and kidney by spectrophotometric methods. Significantly higher Hg concentrations were found in otter hair compared to liver and kidney, particularly in areas with local pollution sources. The rest of the heavy metal(loid)s were recorded at lower concentrations. Positive correlations were observed between Hg and As levels in hair and the liver and kidney. Statistically significant differences in Hg, Cd and Pb concentrations were found between adults and juveniles, as well as between males and females from coastal areas. Moreover, the correlations between heavy metal(loid)s and oxidative stress biomarkers reflected the physiological responses of individuals exposed to these pollutants. The present study is the first to quantify hair metal levels and oxidative status in the European otter from SW Europe. According to our findings, hair demonstrated its suitability as a non-invasive biomonitoring tool for assessing internal Hg and As concentrations, and could be considered in future long-term wildlife biomonitoring programs.