Investigating the Spatial Trends in the Level of Organic Contaminants in the Ethiopian Rift Valley Lakes Using Semipermeable Membrane Devices.

Organic pollutants in the Ethiopian Rift Valley Lakes are the major factors that contribute to severe environmental problem. SPMDs were deployed for the analysis of selected organic pollutants for 1 month at 2 sites in Lakes Hawassa, Ziway and Koka, Ethiopia. From SPMDs placed in the three lakes, the predominant OCPs were DDT which comprise 67% and followed by endosulfan 23% of the total organochlorine pesticides (OCPs) retrieved. The highest level of OCPs, in general, was found in the SPMDs deployed in Lake Ziway with the mean concentration of 308.5 ng/SPMD. However, the concentrations of polychlorinated biphenyls (PCBs) were the highest in the SPMDs deployed in Lake Hawassa with mean concentration of 50.2 ng/SPMD. Spatial variation on the accumulation of OCPs and PCBs among the lakes depends on the shoreline activities, distance of the lakes from point and non-point sources, and the biofouling factors.

Organochlorine pesticides and polychlorinated biphenyls in fish from Lake Awassa in the Ethiopian Rift Valley: human health risks.

Dietary intake of fish containing organic contaminants poses a potential threat to human health. In the present work, an assessment has been carried out to look at the human health risk associated with consumption of fish contaminated with organochlorine pesticides (OCPs) and polychlorinated biphenyles (PCBs) in certain fish species collected from Lake Hawassa, Ethiopia. The health risk assessment was made by comparing the concentrations of OCPs and PCBs in fish muscle tissues with reference doses given in the USEPA guidelines. Dichlorodiphenyltrichloroethanes (DDTs), endosulfans, PCBs and chloridanes were identified in fish species collected from Lake Hawassa. The most predominant pesticides were DDTs, with mean concentrations of ΣDDT ranging from 19 to 56 ng g(-1) wet weights. The highest concentrations of DDTs were found in Barbus intermedius, representing the highest trophic level. PCBs, DDT and endosulfan concentrations found in B. intermedius exceeded the reference dose for children between the ages of 0-1 year (with hazard index of above 1.0). Therefore, consumption of fish from a high trophic level (e.g. B. intermedius) from Lake Hawassa may pose a special health risk to children.

Biomagnification of DDT and its metabolites in four fish species of a tropical lake.

The concentrations and biomagnifications of dichlorodiphenyltrichloroethane (DDT) and its metabolites were examined in four fish species (Clarias gariepinus, Oreochromis niloticus, Tilapia zillii, and Carassius auratus) from Lake Ziway, Rift Valley, Ethiopia. Paired stomach content analysis, and stable isotope ratio of nitrogen (δ(15)N, ‰) and carbon (δ(13)C, ‰) were used to study the trophic position of the fish species in the lake. 4,4'-DDE, 4,4'-DDT and 4,4'-DDD were the main DDTs identified in the fish samples, with 4,4'-DDE as the most predominant metabolite, with mean concentration ranging from 1.4 to 17.8 ng g(-1) wet weight (ww). The concentrations of DDTs found in fish from Lake Ziway were, in general lower than those found in most studies carried out in other African Lakes. However, the presence of DDT in all tissue samples collected from all fish species in the lake indicates the magnitude of the incidence. Moreover, the observed mean 4,4'-DDE to 4,4'-DDT ratio below 1 in C. auratus from Lake Ziway may suggest a recent exposure of these species to DDT, indicating that a contamination source is still present. 4,4'-DDE was found to biomagnify in the fish species of the lake, and increases with trophic level, however, the biomagnification rate was generally lower than what has been reported from other areas. Significantly higher concentrations of 4,4'-DDE were found in the top consumer fish in Lake Ziway, C. gariepinus than in O. niloticus (t=2.6, P<0.01), T. zillii (t=2.5, P<0.02) and C. auratus (t=2.2, P<0.03).

Application of QuEChERS method for extraction of selected persistent organic pollutants in fish tissue and analysis by gas chromatography mass spectrometry.

The QuEChERS method developed for 22 organochlorine pesticides (OCPs) and 7-polychlorinated biphenyls (PCBs) in fish tissue involves a simple and efficient freezing technique for removal of lipids. The equipment developed consists of disposable syringes and a freezing block constructed from simple materials found in most laboratories. The freezing block keeps the temperature in the extract at -20.5°C up to 10 min after being exposed to room temperature. After the freezing step 69% of the lipids in tilapia and 61% in salmon are removed. Further reduction of co-extractives up to 96% in tilapia and 87% in salmon can be made by treatment with CaCl(2) and primary secondary amino sorbent (PSA) which removes the fatty acids. Spiking experiments in tilapia at 5 and 50 ng/g and extracted with acetonitrile show recovery range from 70 to 115% for all compounds. In salmon the recoveries are in the range 43-118% for the OCPs and 26-65% for the PCBs. Analysis of a standard reference material shows acceptable results for most of the pesticides but low results for the PCBs. The estimated LOQs were in the range 1-5 ng/g for tilapia and 2-10 ng/g for salmon. The method has been applied to analyse fish samples from Lake Koka in Ethiopia. It was investigated if addition of a less polar water miscible solvent than acetonitrile could increase the recovery of OCPs and PCBs. The results show that a mixture of 75% acetonitrile and 25% tetrahydrofurane (ACN/THF 75/25) clearly enhances the recoveries for most OCPs (47-101%) and PCBs (42-79%) from salmon. The recovery of aldrin increases significantly from 55% to over 80%. The method using ACN/THF 75/25 is applicable to the extraction of OCPs and PCBs from fish tissue having a lipid content of up to about 11% (salmon) with recoveries ≥70% for most of the OCPs and ≥42% for the PCBs.

Bioaccumulation of persistent organic pollutants (POPs) in fish species from Lake Koka, Ethiopia: The influence of lipid content and trophic position.

The concentrations and bioaccumulation of persistent organic pollutants (POPs) were determined in four fish species from Lake Koka, Ethiopia, representing 2-3 levels in the food chain of the lake. Dichlorodiphenyltrichloroethanes (DDTs), endosulfans, polychlorinated biphenyls (PCBs) and chlorpyrifos were identified, with DDTs as the most predominant pesticide, with concentration ranging from 0.05 to 72.53ngg(-1) wet weight (ww). All fish tissue samples collected from different species of the lake contained residues of DDTs. The maximum level of DDTs was found in the fattiest, African sharptooth catfish (Clarias gariepinus) sampled from the lake, with a mean concentration of 15.15ngg(-1)ww. The significant (P<0.05) relationship between concentrations of DDTs and δ(15)N indicates that DDTs biomagnified in the food web of the lake. The 4,4'-DDE to 4,4'-DDT ratio in Oreochromis niloticus (0.6) and Cyprinus carpio (0.5) were below 1, indicating ongoing use of DDTs in the study area and recent exposure of these fish species.