An assessment of the impact of artisanal and commercial gold mining on mercury and methylmercury levels in the environment and fish in Cote d'Ivoire.

Artisanal and small-scale gold mining (ASGM) activities are an important source of mercury (Hg) to the atmosphere globally, and in most countries in West Africa, where gold production has increased dramatically in the last decade from both commercial and ASGM activities. This study focused on examining the concentrations of Hg and methylmercury (MeHg) in water, sediments and fish in four regions associated with gold mining activities in Cote d'Ivoire to assess the potential exposure of the local communities to MeHg from fish consumption. Concentrations of dissolved total Hg and MeHg in water and sediment were elevated at some locations sample and were indicative of local contamination. Several locations had sediment total Hg above 100 ng g-1 and sediment %MeHg ranged from 0.03 to 4.4%. Fish concentrations exceeded 0.3 µg/ g wet wt., especially for carnivores and fish caught in the western region of the country. Bioaccumulation factors, relative to dissolved MeHg, were higher for carnivores than omnivores and varied with region, suggesting other factors besides MeHg concentration alone were impacting uptake and trophic transfer. Given that people in Cote d'Ivoire consume fish at a higher level than other countries, the levels in fish were sufficient to exceed the US EPA's guidance criteria even at average consumption levels, and particularly for people consuming fish at a higher rate. Overall, this study provides compelling evidence that ASGM activities in Cote d'Ivoire are leading to elevated exposure and likely impacting the health of the local populations in regions where such activity is occurring.

Nitrogen-containing organic compounds: Origins, toxicity and conditions of their photocatalytic mineralization over TiO2.

Sustainable water management remains a global concern to meet the food needs of industrial and agricultural activities. Therefore, pollution abatement techniques, cheap and environmentally, are highly desired and recommended. The present review is devoted to the origin and the toxicity of nitrogen-containing organic compounds in water. The progress made in removing these pollutants, in recent years, is addressed. However, a prominent place is given to the photocatalytic degradation process using the TiO2 as a semiconductor, the conditions for good mineralization and especially the factors influencing it. The parameters that impact the performance of this method are the pH, the temperature, the reactor used, the light, the concentration of the pollutant, the amount of catalyst, etc. Up to now, the importance of one parameter relative to another has not been established because in the context of the photocatalytic degradation, certain parameters are often tightly coupled. Consequently, the mineralization is dependent on the initial degree of oxidation of nitrogen atom contained in the pollutant to be degraded. The hydroxyl nitrogen is primarily converted into nitrate ions (NO3-), while the amides and the primary amines are converted into ammonium ions (NH4+).

Reduction of mercury (II) by humic substances--influence of pH, salinity of aquatic system.

This study demonstrates that under abiotic dark conditions in aquatic system, humic substances are not only capable of converting Hg(II) to Hg(0) but also able to bind Hg(II) ion. The degree of Hg(II) reduction is significantly influenced by the ratio of -COOH/-OH groups and the sulfur content in the HS, revealing a strong competition between complexation and reduction of Hg(II). This study suggests that abiotic and dark Hg(II) reduction depends on the pH and salinity of aqueous medium. At lower pH (∼ 4.0) and lower salinity (≤ 5.0 PSU), the reduction of Hg(II) to elemental mercury (Hg(0)) was comparatively rapid. Higher -COOH/-OH ratios in HS, favors dark abiotic reduction of Hg(II) as did a lower sulfur (S) content of HS. This study provided a rigorously controlled experimental design that showed that dark abiotic Hg(II) reduction by HS can potentially be important in the aquatic environment and is independent of the photochemical reduction observed in both fresh water and sea water.