Mercury concentrations at a historically mercury-contaminated site in KwaZulu-Natal (South Africa).

INTRODUCTION: A mercury (Hg) processing plant previously operating in KwaZulu-Natal Province (South Africa) discharged Hg waste into a nearby river system causing widespread contamination since the 1980s. Although the processing plant ceased operation in the 1990s, Hg contamination (due to residual Hg) remains significant. Previous studies in the area since the plant's closure have found elevated Hg concentrations in fish, and that these concentrations were as a direct consequence of widespread contamination of the Hg processing plant operations conducted between the 1980s and 1990s. OBJECTIVES: This study aimed at investigating the impacts of residual Hg almost 20 years after the plant's closure. METHODS: Water, sediment and biota (invertebrates and fish) were collected in water resources in the vicinity of the processing plant to determine the Hg concentrations in these compartments, as a proxy for assessing the extent to which residual Hg that is reintroduced to the water column becomes bioavailable to biota. For water and sediment samples, higher total mercury (TotHg) and methylmercury (MeHg) concentrations were measured at sampling sites immediately downstream of the Hg processing plant when compared to the upstream sites, while concentrations decreased with distance from the plant. Fish MeHg concentrations measured just below the US EPA guideline for Hg in fish muscle tissue. RESULTS: The results show that the historically Hg-contaminated river system is a potential Hg pollution source due to the residual Hg present in sediment. Any dredging of sediment as a form of remediation in the Mngceweni River is not recommended; however, a Hg monitoring programme is recommended for assessing the bioavailability of resuspended Hg from sediment.

Mercury concentrations in water resources potentially impacted by coal-fired power stations and artisanal gold mining in Mpumalanga, South Africa.

Total mercury (TotHg) and methylmercury (MeHg) concentrations were determined in various environmental compartments collected from water resources of three Water Management Areas (WMAs) - viz. Olifants, Upper Vaal and Inkomati WMAs, potentially impacted by major anthropogenic mercury (Hg) sources (i.e coal-fired power stations and artisanal gold mining activities). Aqueous TotHg concentrations were found to be elevated above the global average (5.0 ng/L) in 38% of all aqueous samples, while aqueous MeHg concentrations ranged from below the detection limit (0.02 ng/L) to 2.73 +/- 0.10 ng/L. Total Hg concentrations in surface sediment (0-4 cm) ranged from 0.75 +/- 0.01 to 358.23 +/- 76.83 ng/g wet weight (ww). Methylmercury accounted for, on average, 24% of TotHg concentrations in sediment. Methylmercury concentrations were not correlated with TotHg concentrations or organic content in sediment. The concentration of MeHg in invertebrates and fish were highest in the Inkomati WMA and, furthermore, measured just below the US EPA guideline for MeHg in fish.