Spatial Trends and Profiling of Persistent Organic Pollutants (POPs) in Lakes of Lesser Himalayan Region (LHR), Pakistan

Abstract

Persistent organic Pollutants (POPs) are group of synthetic organic chemicals. Due to unique properties of POPs such as non-degradability, lipid affinity and volatility, this group of chemicals find its wide application in agricultural and industrial sectors. However, these properties also make POPs a cause of concern because, due to volatility, these pollutants have undergone long range atmospheric transport and deposited in the remote regions where they have never been used or produced. Lower temperature, snow cover, high altitude and vegetation cover of remote regions have made them to act as condenser for volatile and semivolatile POPs. The mountainous lakes act as final sink for atmospherically transported POPs and an eye for environmental changes in the region and respond directly to the environmental changes in the catchment area. Due to lipophilicity, the deposited POPs in lakes start to accumulate in aquatic environment and biomagnified along food chain and exhibited detrimental ecotoxicological impacts on aquatic biota as well as in human beings. The Himalaya is the largest mountain range located in north of Tibetan Plateau and present as an arc of 2400 km in sub-continent and influenced by summer monsoons and westerlies. The Himalayas are wedged between India, China and Pakistan, which are densely populated, rapidly developing industrial and agricultural zone of the world and are major emitter of POPs. Due to proximity of Himalayas to the major consumer of POPs in the world, the remote mountains are greatly impacted by POPs. The lakes in eastern and central part of Himalaya are widely studied to determine the role of limnic systems in fate and cycling of POPs in remote environment. Current study was designed to assess the role of different lakes i.e., urban remote and glacial lakes in accumulation and fate of POPs in lesser part of western Himalaya. Since lesser Himalayas are relatively close to the sources of POPs and are expected to be greatly impacted by proximal sources of POPs in the region. For this purpose, air via PUF-PAS and soils were sampled near to the selected lakes, whereas fish and sediments were collected form lakes. Whole sampling procedure was conducted according to defined protocols. All the collected samples were analyzed for OCPs, PCBs and PBDEs by GC–MS. Whereas total organic carbon (TOC) and BC were analyzed in soils and sediments by Chemo-Thermal Oxidation (CTO-375) method. Abstract x Concentrations of OCPs PCBs and PBDEs in soil, 0.21- 2.8 ng g-1; 0.81-4.8 ng g 1 ; 0.089-0.75 ng g-1, air 0.10 - 147 pg m-3; 0.013-182 pg m-3; 0.011-8.2 pg m-3, sediments 0.01-1.48 ng g-1; 0.23-2.05 ng g-1; 0.01-0.19 ng g-1and fish 0.18-447 ng g-1lw; 6.4-138 ng g -1lw; 1.1-14 ng g-1lw, respectively. Overall, all matrices of urban lakes (soil, air, sediment and fish) showed higher level of contamination indicated the influential role of sources present in proximity of the region. The Clausius–Clapeyron relation (ln P vs inverse of temperature 1000/T; K) showed statistically significant association (p ≤ 0.05) for OCPs and PCBs at urban lakes indicated that these regions are greatly influenced by local sources of POPs. Insignificant CC relation (p > 0.05) coupled with backward air mass trajectories suggested that LRAT is major source of PCBs OCPs and PBDEs in remote and glacial environment. Similarly, regression analysis between SOM and POPs in soils indicates that BC at glacial lakes, TOC at remote and both BC and TOC in urban lakes explain the soil air portioning of POPs. Fugacities of POPs processes indicate that re-volatilization at glacial lakes whereas deposition at remote lakes are the dominating processes in soil-air exchange of POPs. Similarly, trophic position and dietary pattern of fish explains the significant variation in level of POPs among species. The pots of self-organizing map (SOM) suggested that type of lake (urban, rural and glacial) and source distribution are important descriptor of variability in distribution of POPs between different fish species among lakes of LHR. Moreover, although lower levels of organic contamination were observed in fish form glacial lakes and remote mountainous lakes, however, LRAT, continuously increasing anthropogenic activities and glacial melting present potential threat to the remote environment of LHR. The sediment cores from lakes of LHR showed variable level of OCPs, PCBs and PBDEs in different lakes. However, depth dependent distribution of POPs in sediment core samples was observed and reflected a general increasing trend form bottom to top sediment layers. These results suggested that region of LHR is influenced by but continuous input of POPs. The findings of this study reported the level, trends and profile of POPs in matrices of different lakes of lower stretch of Himalaya. This study will help in better understanding the role of Himalayan lakes in biogeochemical cycling of POPs along Indus basin. Further studies are required to understand the role of lakes in transport, fate and distribution of POPs in high altitudinal remote Himalayan environment.