A Human Health Risk Assessment of Heavy Metal Bioaccumulation in Nile Tilapia Oreochromis niloticus from Lake Chivero, Zimbabwe

Abstract

Lake Chivero’s catchment covers the urban areas of Harare and Chitungwiza, which contribute immensely to the pollution of the lake through urban runoff, sediments, sewage effluents, industrial effluents and leachate from landfilled areas along river banks. Heavy metal pollution has been observed in water, sediments and fish in Lake Chivero and in rivers within its catchment. Accumulation of these heavy metals in fish poses serious health risks to fish consumers. The purpose of this study was to assess non-carcinogenic and carcinogenic health risks to human adults living in communities around Lake Chivero due to fish consumption. Concentrations of lead, zinc, cadmium, arsenic and manganese were measured in whole gutted Nile Tilapia (Oreochromis niloticus) from Lake Chivero. In a survey to establish fish consumption patterns in communities around Lake Chivero, 203 people residing in Lake Chivero residential area, Kuwadzana Extension, Whitecliff and Dzivarasekwa were interviewed, from which data non carcinogenic and carcinogenic risks were calculated using standard methods. When metal concentrations were regressed with fish total length statistically significant (p < 0.5) weak positive correlations were observed for lead, cadmium and arsenic, and a statistically significant (p < 0.5) weak negative correlation was observed for zinc. There was no significant correlation (p > 0.5) between fish total length and manganese concentration. In the four communities surrounding Lake Chivero there were no significant differences in fish intake rate (per event), exposure frequency, and body masses, however there were some significant differences in exposure duration. There were no significant differences in fish consumption patterns between males and females, although their body masses differed significantly. Lead concentrations in fish were very high putting fish consumers at risk associated with the potential toxicity of the metal. At least 85% of interviewees were at risk (non carcinogenic hazard index > 1) due to exposure to arsenic, at least 44% due to exposure to cadmium, 10% due to exposure to manganese and 0% due to exposure to zinc. Carcinogenic risk was only determined for exposure to arsenic because of the availability of a standard slope factor for this metal in literature, and it ranged from 206 to 793 people per million (0.2 – 0.8 %). It was therefore concluded that fish consumers around Lake Chivero are at risk due to exposure to heavy metals. There is need for development of fish consumption guidelines. Local authorities, stakeholders and environmental authorities are therefore urged to work together in concerted efforts to reduce pollution of the lake.