Biomonitoring of mercury in water, sediments, and fish (brown and rainbow trout) from remote alpine lakes located in the Himalayas, Pakistan

Mercury (Hg) contamination of aquatic ecological units and subsequent bioaccumulation are major environmental problems of international scope. Moreover, the biogeochemistry of Hg in the remote alpine lakes aquatic ecosystem in the Himalayas remains largely unexplored. The current study investigated Hg concentrations in different environmental compartments such as water, fish, and sediments in the remote alpine lakes (RALs) including Glacial-fed Lake, Ice melting-fed Lake, and Rain-fed Lake in northern areas of Pakistan. The mean concentration of Hg in Rain-fed Lake water was (1.07 µg L⁻¹), Ice melting-fed Lake (1.16 µg L⁻¹), and Glacial-fed Lake (1.95 µg L⁻¹). For fish muscle tissues, mean concentration of Hg was 1.02 mg kg⁻¹ in the Rain-fed Lake, and 1.2 mg kg⁻¹ for the Ice melting-fed Lake, and 1.51 mg kg⁻¹ in the Glacial-fed Lake. Meanwhile, 0.27 mg kg⁻¹ was observed for sediments in the Rain-fed Lake, 0.33 mg kg⁻¹ for the Ice melting-fed Lake, and 0.38 mg kg⁻¹ for the Glacial-fed Lake, respectively. Chronic daily intake (CDI) and potential health quotient (PHQ) for water showed high health risk in Glacial-fed Lake and low in Rain-fed Lake (PHQ < 1). The target hazard quotient (THQ) values for both the Brown and Rainbow trout in all the studied lakes water were less than 1, indicating no health risk. Furthermore, the Hg level showed high level of contamination in the sediments of all the studied lakes (190 ≤ RI < 380). Overall, Glacial-fed Lake water was more polluted with Hg, as compared to Rain-fed Lake and Ice melting-fed Lake. In the light of the abovementioned results, further research work is urgently needed to shed light on the biological and geochemical monitoring of Hg in arid high-altitude ecosystems along with source identification, mercury speciation, and other potential pollutants.