Assessment of Selected Persistent Organic Pollutants in River Ravi and Its Northern Tributaries, Pakistan

Abstract

The persistent organic pollutants (POPs), particularly organochlorines are of key global concern due to their persistence and toxicity in the environment. The present study investigated the occurrence levels, spatio-temporal distribution, risks to both, ecological integrity and human health through dermal and oral exposure to the organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) across River Ravi and its three northern tributaries (Nullah Bein, Nullah Basantar and Nullah Deg) that provides the baseline data for the occurrence of POPs from the study area. The present study is a pioneer investigation from Pakistan to assess the bioavailable level of POPs using mussels as bioindicator species. The water (n=54) and sediments (n=54) samples from twenty-seven sampling sites and freshwater mussels (n=30) samples from fifteen sampling stations were collected across the four aforementioned streams in two alternate seasons (pre-monsoon and post-monsoon). The ∑23OCPs concentrations were ranged from 13.61 to 1992.18 ng/g dry weight (dw), 189.66 to 2049.40 ng/g, and 12.89 to 128.16 ng/L in sediment, freshwater mussels and water matrices, respectively. The ∑35PCBs concentrations were ranged from 1.06 to 95.76 ng/g (dw) in sediments, 1.94 to 11.66 ng/L in water, and 25.81 to 135.38 ng/g in freshwater mussel samples. Among the OCPs, the dominance of ΣDDTs, ΣHCHs and Σendosulfan were observed in all three studied environmental matrices. The PCBs homologs analysis indicated that penta-CBs and hexaCBs in sediments and mussels, and tetra-CBs and tri-CBs in water were predominant homologs. Based on the POPs contamination levels, the tributaries of River Ravi followed the contamination order as; Nullah Deg> Nullah Basantar > Nullah Bein and fresh addition of lindane, technical DDTs and chlordane were identified in the study area. The OCs levels in the environment were found to be higher than previous studies from Pakistan and other parts of the world. The ecological risk assessment indicates considerable potential ecological risk ( = 95.17) associated with PCBs contaminations. The ecological risk assessment of OCPs elucidates high risks for endosulfan (αendosulfan) and endrin. The human health risk assessment indicated absence of hazardous (non-carcinogenic) risk through dermal exposure in studied streams; while, the considerable carcinogenic risks associated to aldrin, dieldrin, p,p’-DDT, β-endosulfan and PCBs was found at certain studied sites. The oral exposure to OCs through mussels consumption revealed existence of substantial carcinogenic risk (Hazard Ratio > 1) for OCPs and PCB at both, 50th and 95th percentile concentration in mussel tissues. Therefore, the high levels of ecological risk and carcinogenic human health risk had emphasized an immediate elimination of ongoing OCPs usage and PCBs release in the studied area. Moreover, in Pakistan, comprehensive ecological and human health risk studies, and firm statutory initiatives are needed to be taken in debt to the Stockholm Convention, 2001 to cope up with the OCs contamination in various environmental matrices of the country.