7. Trace Metal Levels in Water and Sediment from the Sakumo II and Muni Lagoons, Ghana

Abstract

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.