In this study, iron and manganese levels dominate the trace metal composition of Sand River water. This is consistent with Edokpayi et al., (2016) who also showed that iron and manganese dominated the trace metals composition of the Mvudi River in Limpopo Province, South Africa. The dominance of iron is because of its high occurrence in different geological formations in Limpopo Province.
The level of both iron and manganese increased after discharge and this indicates that the effluent from the Polokwane sewage treatment works may be a significant source of these two trace metals. The manganese levels after discharge did not exceed the DWAF, (1996) regulations for aquatic ecosystems (0.18 mg/l). DWAF, 1996 does not have any recommended limits for iron in aquatic ecosystems. For irrigation purposes, the DWAF regulations stipulate that the iron levels must be between 5 to 20 mg/l (DWAF, 1996). The levels of iron in the Sand River are below the target suggested by (DWAF, 1996). DWAF suggest that manganese levels for irrigation must range between 0.
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02 to 10 mg/l. The manganese levels are also within the target range. Cadmium levels in the water remained the same before and after discharge. Cadmium levels also fell within the DWAF target range of 0.01 to 0.05 mg/l for irrigation. Copper levels were also the same before and after effluent discharge.
For copper, the DWAF guidelines for irrigation are between 0.2 to 5 mg/l. In this study the copper concentrations were 0.01 mg/l and fell within the target range. The lead levels were the same before and after effluent discharge at 0.09 mg/l. The lead levels were also within the target range (0.2 mg/l) for irrigation.
Zinc levels remained the same before and after effluent discharge. The zinc levels were way below the target range (1-5 mg/l) for irrigation water. However, both iron and manganese are not a threat to the aquatic ecosystem of the Sand River. Edokpayi et al. (2016) reported that manganese levels exceeded the DWAF recommended limits in the Mvudi River. The lack of elevated levels of all the trace metals in the water is probably because there is no mining activity around Polokwane.
There is no evidence from this study to show that the Polokwane smelter deposits airborne trace metals in the Sand River.