Still there: Persistent Organic Pollutants in fish from two Italian high-mountain lakes

Persistent Organic Pollutants (POPs) can accumulate in high-mountain lake fish due to long-range transport. The aim of this study was to determine the presence of 41 POPs included in the Stockholm Convention in muscle and livers of Salvelinus fontinalis collected from two high-altitude lakes in the Cottian Alps (Italy) (Upper Balma Lake and Lower Balma Lake) and to assess differences among lakes and across years (2017–2021). Thirty-nine fish muscle samples and 28 liver samples were extracted using an ultrasonic bath, and analyses were conducted using a Gas Chromatograph coupled to an Orbitrap mass spectrometer (GC–MS-Orbitrap). This procedure was first optimized and validated using spiked cod fish samples, with quality control parameters and method uncertainty provided. The collected fish from both lakes revealed the presence of p,p'-DDE, hexachlorobutadiene, hexachlorobenzene, pentachlorobenzene, and various polychlorinated biphenyls (PCBs) at concentrations ranging from 0.005 to 1.8 ng/g wet weight (w.w.). Principal component analysis (PCA) showed no significant differences over the four years of monitoring or between the two lakes, although older fish exhibited higher contamination levels. These findings confirm that, even more than 30 years after their prohibition, legacy contaminants persist in theoretically pristine remote areas, highlighting the need for continued environmental monitoring. Future research should integrate passive sampling methods and assess the bioavailability and ecological impacts of these pollutants. Additionally, further investigation is required to understand the influence of climate change on the remobilization and transport of POPs in high-mountain aquatic ecosystems.