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Mercury is a persistent heavy metal that has been associated with damage to the central nervous system, including hearing and speech impairment, visual constriction and loss of muscle control. In aquatic environments mercury may be methylated to its most toxic form, methyl-mercury. In 1990 concerns were raised over mercury contamination in the vicinity of a mercury processing plant in KwaZulu-Natal, South Africa. Mercury waste was reported to have been discharged into the Mngceweni River, situated in close proximity to the plant. The Mngceweni River joins the uMgeni River, which in turn flows into the Inanda Dam, along the banks of which several villages are located. This study evaluated the mercury levels in river and dam sediments, fish from the Inanda Dam and hair samples collected from residents of three villages along the banks of the Inanda Dam. The study results showed that 50% of the fish samples and 17% of hair samples collected from villagers had mercury concentrations that exceeded guideline levels of the World Health Organization. Mercury concentrations in 62% of the river sediment samples collected in close proximity to the former mercury processing plant exceeded the level at which remedial action is required according to legislation in the Netherlands. These preliminary findings give reasons for concern and should be used as a baseline for further investigations.

A magnetic anomaly near the centre of the Vredefort impact structure is attributed to remanent magnetism associated with a large meteorite impact at~2.0 Ga. The rocks that underlie the anomaly are shocked Archaean granites, which have extremely high remanent magnetism. We propose that the high remanence derives from elongated, micron-size single-domain magnetite particles found along shock-induced planar deformation features in quartz. The magnetite particles appear to have preferred magnetic dipole orientations, and are interpreted to have been intruded along the planar deformation features under extreme P-T conditions following the impact event.

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