The Densu River Basin constitutes one of the largest agricultural areas in Ghana. The practice of using pesticides such as organochlorines, organophosphates, carbamates, pyrethroids and several others in agriculture and public health programs has raised concerns about potentially adverse effects on human health and the environment. In this study, a field survey was conducted to assess farmers' knowledge of safe handling and use of pesticides. Residues of pesticides in fish samples as well as the potential health risk associated with exposure to these pesticides were also evaluated. Data obtained from the field survey indicate that a very high proportion of farmers are at high risk of pesticide poisoning from occupational exposure. More than 90% of farm workers do not practice safety precaution during pesticide formulation and application leading to considerable prevalence of pesticide related illness in this agricultural community. Pesticide residues in fish samples varied greatly; from 0.10 µg•Kg-1 to 30.90 µg•Kg-1 , consumption of fish and fisheries product from the basin was no zero risk. The estimated dose for aldrin, methoxychlor, γ-chlordane, endrin aldehyde, endrin ketone, endrin, p'p'-DDT and δ-HCH do not pose a direct hazard to human health, although present in fish samples since the values were lower than toxic thresholds as well as reference dose. However, γ-HCH, heptachlor, α-endosulfan, endosulfan Sulphate, p'p'-DDE and dieldrin levels exceeded the reference dose, indicating a great potential for systemic toxicity in children who are considered to be the most vulnerable population subgroup.

The Densu River is a typical river flowing through agricultural areas in Southern Ghana. Six fish species from different locations in the river were sampled and analyzed for residues of pesticides and metabolites using GC with ECD/FID. The results of the study indicate that all the detected residues and metabolites in fish samples from the Densu River Basin were organochlorines (OCs). Among the pesticides residues analyzed, DDE, α-endosulfan, γ-HCH, δ-HCH, heptachlor and endosulfan sulphate, were predominant in all the samples. About 50% of the samples recorded positive detection of DDE while α-endosulfan was detected in 60% of the samples. γ-HCH, δ-HCH were detected in 75% and 65% of the samples respectively with heptachlor occurring in 80% of the samples. In almost all the fish species analyzed, DDE was the predominant compound having a mean value of 7.99 µgKg -1 . Higher concentrations of pesticide residues were detected in fish samples from the Densu River at Nsawam than the other locations. The total concentration of residues in the fish samples ranged between 0.49 µgKg -1 and 8.90 µgKg -1 with the highest level detected in Hepsetue odoe (HO-N). The sequence of pesticide residues detected in fish samples were HO-N > HN-N > CO-N > CG-N > TZ-N > CN-W > TZ-W > CG-W. The high ratio of DDE/DDT in fish samples (0.1 -6.9 with a mean of 2.51) indicated probably old input of DDT and significant degradation. The γ -HCH isomer (lindane) was the dominant HCH in fish samples suggesting a preferential usage of lindane (purified γ-HCH) in these areas. The δ-HCH/γ-HCH ratios in most fish samples were low indicating the present input of the pesticide lindane from non-point sources.

The impact of anthropogenic activities on the fluctuation of nutrients along the Densu River and its tributaries was studied. High concentrations of nutrients were observed in the study area but the river was found to be circumneutral and fresh with pH ranging between 6.54 and 7.84. The levels of NH 4 ? -N ranged between 0.21 and 2.1 mg L -1 with mean concentration of 1.19 ± 0.02 mg L -1 while that of nitrate is between 0.13 and 5.21 mg L -1 with a mean concentration of 2.07 ± 0.01 mg L -1 . The levels of PO 4 3--P fluctuated within the range 0.54 and 1.04 mg L -1 with a mean of 0.84 ± 0.01 mg L -1 . The Densu River Basin was also found to be with organic matter with depleted dissolved oxygen. The river recorded high BOD values ranging from 6.91 to 18.8 mg L -1 . Concentration of nutrients and organic pollutants increased as a consequence of anthropogenic inputs particularly from domestic, agricultural and municipal sources. The highly impaired sites were those located close to the urbanized, agricultural and high-density residential areas. The relatively high concentration of nitrate and phosphate in the river indicated that it was quite eutrophic.

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