Assessment of mercury in sediments and in the benthic invertebrate micronecta scholtzi downstream an abandoned pyrite mine

Abstract

The drainage of abandoned mines leads to several ecological problems, particularly the acidification of surface freshwater systems and heavy metal contamination. Mercury (Hg) is of particular interest because of its high toxicity and its ability for bioaccumulation. This work evaluates the magnitude and pattern of Hg dissipation from an abandoned pyrite mines to the local water ecosystem by testing of the stream bottom sediments and water invertebrate Micronecta scholtzi along the pyrite-cupric mine drainage system. Overall results showed a high significant correlation (Pearson coefficient = 0.82 at p<0.05) between mercury levels in biota and those in sediments for all the sampling sites. In the sediments Hg concentrations ranged from 14.4-32.4 mu g g(-1) dw decreasing downstream to 3.67-5.3 mu g g(-1) due to natural dilution. He, concentration in M. scholtzi showed a similar trend ranging from 3.6-12.6 mu g g(-1) dw at the mine pit and decreasing 5 Km downstream to 0.2-1.6 mu g g(-1) thus reflecting the significant Hg dissipation in surface sediments. Reported Hg levels in sediments were very high and significantly above threshold limits defined by the legislation for the protection of aquatic biota. The Hg in stream sediments derived from such mining areas is potentially hazardous to the environment adjacent to the abandoned mine and this work proves that Hg is mobilised from the mines and accumulated by local water biota, posing a risk to surrounding freshwater systems.