其他摘要 | Cadmium (Cd) is a typical toxic trace metal that poses high environmental risk. Anthropogenic contribution is generally the major source of Cd pollution in the environment. However, natural source may dominate in areas with high Cd geochemical background. Such that research on naturally-induced Cd contamination is a helpful supplement for better understanding of Cd contamination and associated environmental impacts in the environment. This thesis aims to study the distribution pattern, sources, migration, accumulation, and environmental health effects of Cd in a rural area with high Cd geochemical background, from Jianping area in the Three Gorges region. The following findings have been obtained from the study. The local outcroped rocks contained elevated Cd content, pointing to high Cd geochemical background of the study area. Among them, carbonaceous mudstone, siltstone and shale (mean at 2.0 mg/kg), claystone (mean at 29 mg/kg) and stone coal (mean at 25 mg/kg) showed higher Cd contents. The enrichment of Cd in black rock series was probably attributable for the abundant biological materials introduced and the reducing environment during geological deposited. Cadmium and other metals may be existed as sulfides in rocks. Mobility of Cd during rock leaching process was coupled with weathering of the sulfides, and the consequent acidic solution accelerated Cd release. Cadmium contents (0.05-0.36 μg/L) in the local waters were much lower than the safety limits (5 μg/L) of drinking water in China, but it was enriched in the sediments (4.23-9.18 mg/kg) because of higher mobility in the water-sediment system and the source of sediment. Cadmium contents in the collected sediments of Yangtze River (0.84-0.87 mg/kg) were significantly higher than the historical and background values of Cd in the Yangtze River catchment. The local soils significantly enriched for Cd, and the Cd contents were much higher than the background value of Chinese soil. The element distribution in soils showed clear geochemical inheritance with parent rocks. The Cd contents in soils decreased in the order of arable soils (mean at 7.1 mg/kg) > subsoils (mean at 2.6 mg/kg) > natural soils (mean at 2.0 mg/kg), which was mainly constrained by the weathering of parent rocks and gravity flows. Cadmium in soil profiles showed relative enrichment in top soil, which was probably related to high soil organic contents and plants absorption. Enrichment of Cd in local soils was probably contrained by the adsorption effects of clay minerals and Fe oxides, or by the adsorption or complexation of organic materials, or both. Geogenic source was the dominated origin of Cd in the local soils, and the anthropogenic activities, such as coal mining, additionally aggravated accumulation of Cd in soils. Contamination of Cd in arable soils was within moderate level, and the single ecological risk factor was classified as strong ecological risk grade. The comprehensive ecological risk index for Cd graded to moderate ecological risk level, for which Cd was the major contributor. The dominated fractions of Cd in soils were composed of residual (mean at 41%), exchangeable (mean at 21%) and reducible (mean at 21%) fractions, which pointed to high bioavailability of Cd, probably due to low partition coefficient of Cd. Cadmium was significantly accumulated in the local food crops (mean at 0.68 mg/kg), due to the enrichment and high bioavailability of Cd in soils. Cadmium concentrations in Chinese cabbage (mean at 3.57 mg/kg) and green cabbage (mean at 1.12 mg/kg) were higher than other crops, significantly higher than safety limits of Chinese food, due to the higher biological accumulation factors. However, the Cd contents in the locally consumped rice (mean at 0.04 mg/kg) was relative low, compared to the safety limits. Assessment of daily intake and health risks of vegetables, grain and drinking waters indicated that Cd posed high health risk (HRI = 4.62), for which the intake of v |
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