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This study involved the determination of sediment quality and heavy metals in the water column and bottom sediment of a selected cage fish farm in Lake Volta, to assess the potential impact of metals and organic matter pollution on the lake due to cage fish farming. Sediment analysis indicated that the texture of all sampling sites was sandy clay loam with sand dominating with a range of 31.5%–81.2%. The organic matter (TOM) ranged from 4.42%–8.89%, while organic carbon (TOC) was from 2.57%–5.22%. Total nitrogen (TN) fluctuated between 0.22% and 0.45%; total phosphate ranged between 0.22% and 5.30%. The TOC, TOM and TN content in the farm sediment were significantly lower than those of the reference sites (ANOVA, p < .05). Lead, copper, cadmium and selenium were not detected in the water. The results revealed that heavy metal concentrations in the water column and sediments were low and within tolerable levels, indicating no influence of metals from fish feed was observed on the lake water quality. However, the farm seemed to have moderate impact on sediment quality from organic matter. Water and sediment quality monitoring should be embarked upon periodically to ensure sustainable cage culture in the Lake Volta.

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Trace metal (Cu, Zn, Pb, Mn, Fe and Cd) levels were determined in water and sediment from the Sakumo II and Muni lagoons and the Mamahuma and Gbagbla Ankonu feeder streams, which feed the Sakumo II lagoon over a 1-year period, and their occurrences compared. Some physical parameters (temperature, pH and electrical conductivity) were also investigated. The aim of the study was to establish the pollution status of the two lagoons, as well as investigate whether the feeder streams of the Sakumo II lagoon have any influence (in terms of trace metal pollution) on the Sakumo II lagoon. Results showed that upper mean values in water and sediment were Zn ( 0.160 ± 0.01 mg/l, 48.7 ± 0.93 mg/kg), Pb (0.057 ± 0.03 mg/l, 29.2 ± 3.2 mg/kg), Mn (0.798 ± 0.07 mg/l, 668.2 ± 6.3 mg/kg), Cu (0.158 ± 0.01 mg/l), Fe (1.32 ± 0.73 mg/l, 3075 ± 14.7 mg/kg), respectively, for Sakumo II lagoon. Cd levels in water and sediment ranged from 0.004 ± 0.001 to 0.009 ± 0.001 mg/l and < 0.002 to 0.88 ± 0.05 mg/kg respectively, in the Sakumo II lagoon. Compared to the maximum contaminant level (MCL) of 0.005 mg/l, the Cd levels in water from the Sakumo II lagoon may be detrimental to the 'health' of the aquatic ecosystem and, consequently, consumers of fish products from the Sakumo II lagoon. Water and sediment in the Muni lagoon had trace metal concentrations with upper mean values as Cd (< 0.002 mg/l, 0.325 ± 0.01 mg/kg), Pb (0.033 ± 0.01 mg/l, 1.46 ± 0.18 mg/kg), Mn (0.434 ± 0.02 mg/l, 63.8 ± 1.50 mg/kg), Zn (0.077 ± 0.001 mg/l, 13.7 ± 0.18 mg/kg), Cu (0.013 ± 0.001 mg/l) and Fe (1.085 ± 0.26 mg/l, 3198.4 ± 3.51 mg/kg), respectively. Generally, trace metal levels detected in sediment from the Mamahuma ( Zn: 10.4 ± 4.10 mg/kg, Pb: 10.6 ± 1.84 mg/kg, Mn: 63.7 ± 4.5 mg/kg, Fe: 7487 ± 23.5 mg/kg, Cd: < 0.002), and from the Gbagbla Ankonu ( Zn: 155 ± 13.9 mg/kg, Pb: 37.4 ± 3.07 mg/kg, Mn: 298.2 ± 2.5 mg/kg, Fe: 3209 ± 50.5 mg/kg, Cd: 0.70 ± 0.05 mg/kg) feeder streams were relatively higher than those in the Sakumo II lagoon. Sediment from the feeder streams, therefore, provided a deeper insight into the long-term pollution state of the feeder streams and, consequently, the Sakumo II lagoon. The streams could, thus, be described as potential sources of trace metal pollution to the Sakumo II lagoon. Trace metal levels were also found to be more concentrated in sediment from the mid-section of the Muni lagoon than those from the northern and southern sections, while the northern section had more trace metal concentrations in water than those from the mid-and southern sections. The study also showed that trace metal levels detected in both water and sediment from the Sakumo II lagoon were higher relative to those from the Muni lagoon. The Sakumo II lagoon could be described as relatively more polluted with trace metal load.

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An assessment was conducted on the concentrations of zinc, copper, manganese, iron, lead and cadmium in 10 different fish species caught from some coastal and inland waters in Ghana, as part of a project on monitoring of pollution in water bodies in Ghana. Shellfish species (Egeria paradoxa galanata and Atya gabonensis) caught from inland waters had higher elemental concentrations than those caught from coastal waters. Mean concentrations of Fe and Mn were higher in E. paradoxa galanata, A. gabonensis and Trachiurus trachiurus, while Panulirus regius and Sardinella eba had higher mean concentrations of Cu. T. trachiurus, Dentex congoensis and T. ovatus had higher mean concentrations of Pb, while T. trachiurus and S. eba had higher mean concentrations of Zn. Mean Cd concentrations in the fish species were relatively low, with mean concentrations of Cynoglossus cadenati, D. congoensis and T. ovatus below detection limits. The mean concentrations of Zn, Cu, Pb and Cd for shell fishes were comparable to those obtained from previous studies in Ghana. However, they were lower than those reported in other areas of the sub-region. The mean concentrations of Zn, Cu, Pb and Cd in fin fishes were higher than those obtained from previous studies in Ghana. However, these values were comparable to those obtained from other areas in the sub-region. Compared to WHO limits, the levels of Zn, Pb, Cu and Cd in the fish species were lower, and, therefore, safe for human consumption. The study also showed that all the fish species except S. eba, Solar crumophthalmus and P. regius are safe for human consumption with respect to Zn, Cu and Fe.

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