From biomass to fossil fuels: A contemporaneous transition to anthropogenic driven environmental changes recorded in a Central Himalayan Lake

The timings and extent of anthropogenic impacts in the Indian Himalayas are poorly characterized, ambiguous and difficult to determine. In present study, we investigated the compositional variation, concentration, and temporal trend in the polycyclic aromatic hydrocarbons (PAHs) and fecal biomarker (coprostanol and epi-coprostanol) from the lake sediment core in the central Himalayas to determine the fate of anthropogenic activities in Himalayan ecosystems. The total concentration of PAHs (1422–32077 ng/g) and stanols (0.1–5.53 µg/g) showed an increasing trend, with the greatest values recorded after 2000 CE. In addition, the composition of PAHs changed after the 1970s, reflecting the increase in socio-economic activities in the region and the concurrent environmental change. The PAH diagnostic ratios revealed that pyrogenic sources accounted for the majority of the sedimentary PAHs. Moreover, the high correlation between PAHs and fecal stanols indicated the active role of humans in the catchment. Also, our results indicated that the total organic content (TOC%) of sediments and temperature conditions in the region play a significant role in regulating the deposition/burial of PAHs in lake sediments. In addition, based on the toxic equivalency factor (TEF) of PAHs relative to benzo(a)pyrene (BaP) (BaP_eq) and sediment quality guidelines (SQGs), our findings showed an increase in toxicity with values that exceeded the recommendations for the protection of aquatic life, posing a potential toxicological threat to the lake ecosystem and the health of its human residents. As the first such study from the Indian subcontinent, this research is important/key for deciphering the molecular signals of lacustrine records from the region.