Determination Of Persistent Organic Pollutants And Trace Metals In Sediment And Fish Samples From Akaki River Catchment And Aba Samuel Reservoir Central Ethiopia

This Ph.D. thesis describes the occurrence and distribution of selected persistent organic pollutants (organochlorine pesticides (OCPs) and polychlorinated byphenyls (PCBs)) and trace metals (Hg, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in sediment and fish samples from Akaki River catchment and Aba Samuel Reservoir, Central Ethiopia between 2016-2017. The implications of the levels of OCPs, PCBs and trace metals were also evaluated based on national and/or international guidelines. rnEight representative OCPs namely DDT and its metabolites (p, p‘-DDE and p, p‘-DDD), α,-endosulfan, endosulfan sulfate, heptachlor epoxide (B), lindane and dieldrin and indicator PCBs (PCB-28, PCB-52, PCB-101, PCB-118, PCB-138, PCB-153, and PCB- 180) in sediment and fish were determined using gas chromatography-mass spectroscopy (GC-MS), while trace metals were determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and cold vapor-atomic absorption spectroscopy (CV-AAS). rnAnalyzed sediment samples showed the presence of lindane in the dry and p, p‘-DDT, p, p‘-DDE, p, p‘-DDD, , -endosulfan, heptachlor epoxide (B), and dieldrin in the rainy seasons. Lindane and DDTs were the predominant OCPs in the studied regions. Among the indicator PCBs, the analyzed sediment samples showed the presence of PCB-52, PCB-101 and PCB-118 in the dry and all indicator PCBs (PCB-28, PCB-52, PCB-101, PCB-118, PCB-138, PCB-153 and PCB-180) in the rainy seasons. The distribution of PCB congeners in the sediment from Akaki river catchment and Aba Samuel Reservoir showed a predominance of lower chlorinated PCB congeners in the dry and highly chlorinated PCB congeners in the rainy season. A low level of higher chlorinated PCB congeners accumulation suggests a point source contamination. Ecological risk rnassessment of the analyzed OCPs and PCBs using sediment quality guidelines indicated that total DDTs, p, p‘-DDT, p, p‘-DDE and p, p‘-DDD were higher than the maximum residue limit in most of the sampling sites in the rainy season. Then it is possible to conclude that a greater possibility of higher ecological hazards in DDT residues. However, the levels of total PCB concentrations at all sites were below the limit except one site in the dry season. rnAnalyzed fish muscle and liver showed the presence of metabolites of DDT (p, p‘-DDE and p, p‘-DDD), lindane and dieldrin. Among PCBs, only PCB-118 in muscle and PCB-153 in the liver were detected in the dry season. Comparing the concentrations of the present study with international existing limits indicated that 83% of fish muscle samples in both dry and rainy seasons from Aba Samuel Reservoir exceeded the permissible limits with respect to DDTs (14.4 g/kg ww, USEPA (2000)). Similarly, 100% of our fish samples in the dry and 17% of fish samples in the rainy seasons were found to be overloaded with lindane (10 g/kg ww, European Union). However, indicators PCBs were within the permissible limits. rnThe concentration of THg found in all the sediment samples were below the US EPA guideline value of 200 g/kg dry wt. The THg concentrations found in Clarias gariepinus were within the acceptable guidelines of the FAO/WHO. Therefore, the muscle of Clarias gariepinus from the study area is not hazardous to human health with respect to mercury. However, the average value of THg seems to be slightly higher than results reported from other Ethiopian freshwater bodies. Thus, monitoring of mercury species in sediment and different organs of fish are strongly recommended. rnThe trace metals analyzed in surface sediments occurred in varying concentrations along the course of the sampling stations. Ecological risk assessment using USEPA sediment guidelines, geo-accumulation index, contamination factor and pollution load index revealed the widespread pollution by Cd and Pb. These were followed by Mn, Ni and Zn. On the other hand, the levels of trace metals in the muscle of Clarias gariepinus were above the permissible limits for Cr, Fe, Mn, Ni and Pb.

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