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With the aim of revealing the potential ecological risk and distribution characteristics of heavy metals on the surface sediment at the Shawan River section of Yelang Lake, the following three analyses were first performed: (1) analysis of grain-size composition on sediment samples collected at seven different sites in the water-level-fluctuation zone (WLFZ); (2) analysis of bulk sediment content of six heavy metals, namely, Cd, Cr, Pb, Mn, Zn, and Cu; and (3) the correlation analysis of grain-size composition and heavy metal content in the sediment. Afterwards, the approach of Hakanson potential ecological risk index was employed to analyze the risk of heavy metal pollution in sediments of seven WLFZ plots. The outcomes indicate that (1) the mean sediment grain size at each sampling site was generally >0.063 mm, with gravel grains (>1 mm) and sand grains (0.22–1 mm) accounting for the largest proportions; (2) the site-averaged mean sediment content of each of the six heavy metals was significantly higher than their respective geochemical background contents in the sediment of Guizhou Province, and the grain-size dependence of the bulk sediment content of heavy metals was not significant; (3) the distribution of Cr was relatively independent of other metals, which was in contrast to notable positive correlations observed between other metals; and (4) in accordance with the approach of Hakanson potential ecological risk index, for these heavy metals, their potential ecological risk reduced by the order of Zn < Cr < Cu < Pb < Cd, with Cd having a mean potential risk index (Ei) of 566.13, suggestive of a very high level of potential ecological risk, Zn, Cr, and Cu having a mild potential ecological risk, and Pb having moderate potential ecological risk. Cd largely contributes to the comprehensive ecological risk index RI is the largest, thereby having important environmental implications. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) has remarkable toxicological effects on humans, plants, and other lives in the environment, which may restrict the comprehensive utilization of biomass source in view of possibly forming biohazardous waste. In this study, a kinetic study of MeHg degradation under UVB, UVA, natural light, and dark was carried out. The result showed that light radiation enhanced MeHg degradation but had no significant influence on the final balance between MeHg and inorganic mercury (Hg2+) in pure water. The balance is of great importance and can be used as a key fundamental to estimate MeHg cycling in other complicated aquatic environments. MeHg degradation was identified to be second-order reaction using the fitting optimization level of the regression equation, and the second-order rate constants were 1.61, 0.82, and 0.91 L·ng−1·d−1, half-lives were calculated to be 0.62, 1.3, and 1.08 d for UVB, UVA, and natural light, respectively. A possible MeHg degradation mechanism was proposed, and it could perfectly explain the results obtained in this paper and some previous studies. [ABSTRACT FROM AUTHOR]

The spatial patterns, ecological risks, and sources of heavy metals (HMs), including Pb, Zn, Mn, Cu, Cd, Hg, and As in river sediments, were identified around a lead-zinc mine of Danzhai, Guizhou, China. The concentrations of selected HMs and their coefficient variations indicated that the river sediments around this typical lead-zinc mine were obviously contaminated with HMs. Anthropogenic activities had further enhanced the accumulation of HMs. The higher contents of the most common selected HMs were mainly distributed in the area close to the lead-zinc mine. Based on the combined evaluations of the single factor pollution index, geo-accumulation index, and potential ecological risk index, it indicated that the ecological risks of Hg, Cd, Zn, and Pb were high or extremely high, and of Mn, Cu, and As were slight or none in the sediments around this lead-zinc mine. It was found that lead-zinc mining and smelting activities, coal mining activities, and agricultural activities (livestock and poultry breeding) are the primary sources of selected HMs, based on the results of correlation analysis together with principal component analysis (PCA) and positive matrix factorization (PMF) model. The pollution of HMs in the river sediments around a lead-zinc mine was predominantly caused by lead-zinc mining and smelting activities. Therefore, for environmental persistence, lead-zinc mining and smelting activities should be given careful consideration and under close surveillance. [ABSTRACT FROM AUTHOR]