Mercury contamination history of an estuarine floodplain reconstructed from a 210Pb-dated sediment core (Berg River, South Africa).

Mercury deposition histories have been scarcely documented in the southern hemisphere. A sediment core was collected from the ecologically important estuarine floodplain of the Berg River (South Africa). We establish the concentration of Hg in this (210)Pb-dated sediment core at <50 ng g(-1) Hg(T) throughout the core, but with 1.3 ng g(-1) methylmercury in surface sediments. The (210)Pb dating of the core provides a first record of mercury deposition to the site and reveals the onset of enhanced mercury deposition in 1970. The ratio of methylmercury to total mercury is relatively high in these sediments when compared to other wetlands.

The effect of thiolate organic compounds on methylmercury accumulation and redistribution in sheepshead minnows, Cyprinodon variegatus.

Methylmercury (CH3Hg(II)) was measured in various tissues and whole body of sheepshead minnows; Cyprinodon variegatus, following exposure to 100 ng/L methylmercury chloride (CH3HgCl) alone or in combination with one of the organic compounds cysteine (CH3Hg-Cys), thiourea (CH3Hg-Thu), or thioglycolate (CH3Hg-Thg). Overall, the CH3Hg(II) concentration in sheepshead minnows in all the treatments increased with time and was significantly different from the unspiked controls after 24 h. Addition of the organic compounds increased the bioavailability of CH3Hg(II) in the whole body of the fish after 72 h. In particular, the CH3Hg(II) concentration after CH3Hg-Thg and CH3Hg-Thu exposure was, respectively, approximately 1.3- and 1.6-fold higher than with CH3HgCl exposure. A composite of the CH3Hg(II) concentrations in the visceral organs (gill, liver, and intestine) highlighted the effect of the organic compounds, where concentrations in all mercury-thiolate treatments were significantly higher than CH3HgCl alone after 72 h. The most dramatic changes in the different tissues measured were observed in the liver, where the CH3Hg(II) concentrations in the sulfur treatments were significantly higher than the CH3HgCl treatment after 72 h. The results of this study suggest that the CH3Hg-thiolate complexes were bioavailable to sheepshead minnows and effectively induced CH3Hg(II) uptake in tissues at environmentally realistic CH3HgCl concentrations.