Organochlorine Residues in the Riverine Ecosystem of Pakistan

Abstract

Present study aimed to provide the detailed data on Organochlorine Pesticides (OCPs) and Polychlorinated Biphenyls (PCBs) concentrations, possible sources, their seasonal variation, bioaccumulation and risk assessment. For this purpose; water, sediment and fish samples were collected from 25 site locations at River Chenab, during May 2007 to November 2009. Water samples were extracted by liquid-liquid extraction while sediment and fish samples were Soxhlet extracted, cleaned by column chromatography and finally analyzed by Gas Chromatography/Mass Selective Detector (GC-MSD). Concentration (ng/L) in surface waters (including particulate phase) of River Chenab ranged from 27-1100 and 25-1200 for OCPs and 7.7-110 and 13-99 for PCBs during summer and winter, respectively. Dichlorodiphenyltrichloroethane (DDTs) exhibited the highest concentration in all water samples following by Hexachlorocyclohexane (HCHs), Chlordanes, PCBs and other OCPs in descending order, respectively. DDT and PCB levels in surface water exceeded existing criteria concentration guidelines of USEPA. The concentrations (ng/g, dry weight) in sediment ranged from 29-831 and 11.4-811 for OCPs and 9.3- 129 and 12.5-144 for PCBs during summer and winter seasons. The risk evaluation highlighted the burden of γ-HCH, heptachlor, dieldrin and DDTs levels in 70% sediments, while PCBs concentration in 35% of sediment exceeded Effect Range Low (ERL) and Threshold Effect Level (TEL) values. Different indicative ratios for organochlorine residues in both water, and sediment suggested current use, long range transport along with past application of these chemicals. Statistical analysis highlighted agricultural and industrial activities and municipal waste disposal as main source of OCPs and PCBs in the riverine ecosystem of River Chenab. The level of OCPs and PCBs from feeding tributaries (i.e. S20) was relatively greater as compared to those collected from the River Chenab mainstream. The detection frequencies and concentrations of all OCPs and PCBs in water and sediment were higher in winter than those collected in summer season. OCPs and PCBs concentration (ng/g WW) ranged from 13-106 (mean; 38) and 3.1-93.7 (mean; 20) for five herbivorous fish species and 21.5-365 (mean; 148) and 2.4-108 (mean; 30) for six carnivorous species. DDTs, β-HCH, Page XVIII Chlordanes and PCBs detected in fish from distinct trophic levels highlighted biomagnifications. Risk assessments of OCPs and PCBs indicated that fish intake would pose a health risk to human. The findings of present study highlighted the contamination of OCPs and PCBs in River Chenab and there is an urgent need to mitigate the situation. The results can also be helpful for future management of other fresh water resources in the same region.