Fractionation of toxic trace elements in soils around Mo-Ni black shale-hosted mines, Zunyi region, southern China: Environmental implications.

Abstract

This paper examines the influence of Lower Cambrian metal-rich black shales and locally mined black shale-hosted Ni-Mo ore layers of southern China on the concentrations of selected toxic trace elements in soils. In order to better understand the mobility of toxic trace elements, and to evaluate the potential risk of environmental contamination, a sequential extraction analysis from soil horizons A, B, C 1 and C 2 in the area of the Jiepo-Ling Mo-Ni mine (Zunyi region) was carried out. Geochemical analyses confirmed significant enrichments of As, Mo, V and slightly lower proportions of Pb and Ni in the A-horizon relative to a local reference sample of uncontaminated soil. This contamination is anthropogenic, probably caused by the release of metal-rich black shale particles during mining operations. Conversely, the distribution of V and Cr in soils is controlled by the host rock. The results of sequential extraction analyses from individual soil horizons showed that almost all As, Ni, V, Cr and Zn are bound to the residual fraction. Some of the Mo (15.13-39.75%) was found to be associated with the organic matter/sulphide fraction. The distribution of Pb and Hg is erratic, indicating considerable mobility of these elements in the soil profile. In Hg-enriched horizons (B and C 1 ) most Hg (78.21-78.95% of the total content) occurs in the organic matter/sulphide fraction. The concentrations of Mo, Ni, Cr, V, Zn and Hg found in different parts of selected agricultural plants (e.g., tobacco leaves, corn grains, corn leaves, and corn stalks) exceed normal values given by Kabata-Pendias & Pendias (1984). We emphasise that long-term consumption of these products could result in serious health problems for the human population and domestic animals. Arsenic and lead concentrations were found to be within the range of normal values given for agricultural plants.• Key words: metals in soils, extraction analyses, metal-rich black shales, environmental implications, south China.

Black shales contamination and depositional paleoenvironment during the Early Aptian OAE 1a in the Eastern Russian Platform

“…In the Cretaceous, Biscutum suffered the presence of toxic metals introduced in large quantities via hydrothermal plumes (Erba 2004). Similar enrichment in Mo and some other toxic elements are reported to be observed in Lower Cambrian black shales in southern China (Poňavič et al 2006).…”

“…The degree and extent of toxic-metal pollution in recent sediments as a result of human activities has been one of the main topics studied in environmental geochemistry. In addition to anthropogenic metal inputs, high levels of potentially toxic elements are present in natural geochemical materials, such as Cd, Mo, and other heavy metals in black shales throughout the world (e.g., Atkinson 1967, Vine & Tourtelot 1970, Lund et al 1981, Lee et al 1998, Poňavič et al 2006, Ketris & Yudovich 2009.…”

Geochemistry of major and trace elements and Pb–Sr isotopes of a weathering profile developed on the Lower Cambrian black shales in central Hunan, China

“…The weathering of black shale has therefore received substantial research attention, especially the chemical changes during weathering (e.g., Littke et al, 1991;Jaffe et al, 2002;Xu et al, 2013). Such chemical changes are generally explained by mineral dissolution, secondary mineral formation, cation exchange and loss and gain of amorphous oxide phases ; and references therein), during which most metals, including Cd, Co, Mn, Mo, Ni, U, Zn, and PGE, are lost from shales (Peucker-Ehrenbrink and Hannigan, 2000;Jaffe et al, 2002;Peng et al, 2004;) and others are enriched in soils derived from the shales (e.g., Chon et al, 1996;Lee et al, 1998a;Pašava et al, 2003;Poň avič et al, 2006;Peng et al, 2009b;Tang et al, 2009;Yu et al, 2012;Xu et al, 2013). The enrichment of metals in the soils may represent the geopollution of heavy metals.…”

Effect of weathering on abundance and release of potentially toxic elements in soils developed on Lower Cambrian black shales, P. R. China

“…Consequently, the toxic trace elements pose a threat to local human health by entering the food chain. These kinds of issues have previously been addressed by: (1) assessing the environmental contamination caused by black shale soils distributed in different parts of the world (e.g., Lee et al 1998a, b;Pašava et al 2003;Peng et al 2007Peng et al , 2009aYu et al 2008Yu et al , 2009); (2) determining the phases and species of the toxic metals in the soils (Poňavič et al 2006;Lee et al 1998b);and (3) assessing the possible impacts on ecological systems (Lee et al 1998a;Fang et al 2002;Pašava et al 2003;Peng et al 2009a) and on human health (Lee et al 1998b;Fang et al 2002;Peng et al 2004;Poňavič et al 2006).…”