Ecological risk assessment of organochlorine pesticides and polychlorinated biphenyls in water and surface sediment samples from Akaki River catchment, central Ethiopia

Abstract

The current status of persistent organic pollutants in Ethiopian environment is not well monitored despite the existing pollution potential from a number of sources. Water and sediment samples collected from Akaki River catchment and Aba Samuel Reservoir, Central Ethiopia were analyzed to assess the concentrations, distribution, possible sources and potential ecological risk of eight organochlorine pesticides (OCPs) and seven polychlorinated biphenyls (PCBs). Water and sediment samples were extracted by liquid-liquid and Soxhlet extraction respectively, and analyzed using gas chromatography-mass spectroscopy (GC-MS). The detectable OCPs and PCBs in water samples were DDT, DDE, DDD, lindane and dieldrin and PCB-28, PCB-101 and PCB-118, respectively in the rainy season. Analyzed sediment samples showed the presence of lindane in the dry and p, p’-DDT, p, p’-DDE, p, p’-DDD, α, β-endosulfan, heptachlor epoxide (B), and dieldrin in the rainy seasons. Among the indicator PCBs analyzed, sediment samples showed the presence of PCB-52, PCB-101 and PCB-118 in the dry and all indicator PCBs in the rainy seasons. Sources analysis showed that PCBs and detected OCPs were mainly from the historical input of commercial products, but there were recent discharge of DDT and lindane into the river system. Ecological risk assessment of the analyzed OCPs and PCBs using water and sediment quality guidelines indicated that lindane in the dry and p’-DDT, p, p’-DDE, p, p’-DDD, heptachlore epoxide and dieldrin in the rainy seasons in the sediment samples from Akaki river and Aba Samuel reservoir were above the limit at most of the sites. This suggests there is greater possibility of higher ecological hazards in these residues. However, the levels of total PCB concentrations and other OCPs at all sites were below the limit and thus their potential ecotoxicological risks were rather low.