An assessment of the degree of mercury (Hg) bio-transformation in two river systems following discharges from a mercury recovery plant

Abstract

Numerous reports in the media, between 1986 to 1990, have referred to discharges of Hg waste from Thor Chemicals in Kwa Zulu Natal, South Africa into two river systems. A study conducted in 1990 found that Thor Chemicals was the source of this pollution and that excessive levels of Hg were detected immediately below the plant. No other studies have been conducted since then. This study, which includes the are area directly below Thor Chemicals to the top end of Inanda Dam, shows that Hg levels in sediment below the plant were of a similar magnitude to those detected 8 years previously. However, sediment and algae levels further downstream were considerably lower. A 98% increase in Hg sediment levels is noted at a sample site 10 kilometres downstream from the chemical plant. This may suggest that a degree of bio magnification may have taken place, although other factors could also be responsible for this increase.

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