A methodology for undertaking freshwater fish chemical contaminant surveys for human health risk assessment
Du Preez, Hein Hildegarde
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In South Africa the pollution of freshwater aquatic systems can be linked to point source discharges (waste water treatment works and industrial effluents) and diffuse surface runoff (agricultural, mining and urban). As a result of these anthropogenic activities, innocent people as well as other life forms may be exposed to harmful contaminants, which may be released without adequate consideration of human health and the environmental effects. Studies have shown that when people are exposed to surface water contaminants through contact recreation, drinking water and the consumption of contaminated food their health may be affected. Although the consumption of fish is generally beneficial to people (good source of protein, vitamins, omega fatty acids and basic minerals) consumers of fish are potentially at risk as fish have the potential to bioaccumulate contaminants from the aquatic environment that pose carcinogenic, genotoxic and non-carcinogenic health risks to them. As a result of the potential health risk associated with the consumption of chemical contaminated non-commercially caught fish, the United States of America Environmental Protection Agency (US EPA) has developed a series of four guiding documents for issuing fish consumption advisories. The fish consumption advisories are designed to reduce the risk to fish consumers by providing information that would lead to the voluntarily restriction of fish consumption to levels that pose limited, if any risk. A review of the published literature revealed that several surveys were undertaken in South Africa to investigate chemical contaminants in freshwater fish. Most of these studies were aimed at contributing to the assessment of the health of the aquatic ecosystem under investigation as they focused on species and tissue differences in contaminant bioaccumulation as well as the spatial and temporal variation in contaminant concentrations. The health risks to humans when consuming contaminated fish are seldom addressed. Furthermore, no standard methodology as for example suggested by the US EPA was followed by the different investigations. This shortcoming limits comparison of data from different studies and prevents accurate determination of risk based fish consumption limits for humans. To address this limitation the general objective of this dissertation is to develop a generic methodology that would give guidance in the undertaking offish contaminant surveys to provide information regarding the possible health risk if the fish are consumed by recreational and subsistence fisherman. Furthermore, the methodology would also give guidance to surveys investigating the chemical contamination offish for ecosystem health assessment programmes. The fundamentals of the methodology are based on catchment information (possible anthropogenic activities that can result in chemical pollution), socio-demographic information of consumers of freshwater fish in the catchment, bioaccumulation potential and health risks of analytes, sound sampling design, risk assessment procedures and performing monitoring at different scales and depth. The methodology identifies ten major steps, namely: (i) selection of scale and depth of survey, (ii) assessment of the waterbody catchment, (iii) monitoring system design, (iv) field collection, (v) laboratory sample processing and analysis, (vi) analysis of and reporting of results, (vii) risk assessment, (viii) risk management, (ix) risk communication and (x) evaluation and review of the programme which are discussed to provide guidance to governmental authorities at national or provincial level and project managers. The basic requirements of each step are highlighted as limited resources (financial, infrastructure and skilled personnel) in South Africa would limit the possibility of undertaking detailed assessments as undertaken by the United States of America Environmental Protection Agency (US EPA). Nevertheless, by applying the proposed methodology, sound comparable assessments, based on risk assessment methodology, can be made regarding the human health risk associated with the consumption of freshwater fish in South Africa. The study on the Vaal River Barrage Reservoir and the Klip River indicated that there is potential metal health risks (mainly nickel related) associated with the daily consumption of fish from this system. The finding of this study therefore supports the viewpoint that by monitoring the chemical contaminant levels in freshwater fish and applying a risk-based approach valuable information regarding the possible health risk to the consumers of fish (especially to recreational and subsistence fisherman) can be obtained. These surveys also identify areas in the aquatic system where aquatic life and especially fish have unacceptable chemical contaminant levels due to anthropogenic activities in the catchment. This information can thus be used in catchment management programmes and thereby contribute to the management of the catchments in South Africa. From the foregoing it is evident that by following and implementing the methodology proposed in this dissertation a major contribution would be made towards the protection of the consumers of freshwater fish as well as to the protection the of freshwater aquatic environment. These studies are therefore essential for achieving the ultimate goal of ensuring that the fish populations are fit for present and future human consumption. As the Department of Water Affairs and Forestry is the custodian of freshwater systems in South Africa, the monitoring of chemical contaminant levels in fish according to the proposed methodology should be implemented and managed by the Department in collaboration with other governmental organisations and the Catchment Management Agencies.
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