Environmental Biogeochemistry of Trace Elements in the Supergene Environment of Huainan and Huaibei Mining Areas
Student thesis: Doctoral Thesis
In the present research work, a total of 36 subsidence water samples, 36 surface sediment samples, 36 fish samples, 40 surface soil samples and 40 earthworm samples were collected from the Huainan coal mining area. Meanwhile, 6 sediment samples of subsidence pools and 12 corn cobs with 12 corresponding surface soil samples were gathered from the Huaibei coal mining area, respectively. Based on the environmental analysis methods such as acid digestion, BCR sequential extraction and inductive coupled plasma mass spectrometry analysis, and data analysis methods such as correlation analysis, factor analysis, hierarchical cluster analysis, regression analysis and risk assessment, the distribution, speciation, sources, driving factors and potential risk of trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in the supergene environment of Huainan and Huaibei coal mining area were investigated.
The major findings of the present research work were as follows:
(1) The distribution, bioaccumulation and health risk of trace elements (As, Cd, Cr, Cu, Ni, Pb and Zn) in various tissues of fish from subsidence pools in the Huainan coal mining areas were identified. The study found that microelement concentrations in the tissues of Carassius auratus Gibelio collected from subsidence pools were higher than those in the reference natural water body. Trace element levels in tissues are different (liver>gills>skin>muscles) due to the different roles of tissues in metabolism. The bioaccumulation of trace elements in fish was greatly affected by close contact and intake of sediments in pools. There was no risk from the analyzed elements for fish consumption by inhabitants in the Huainan Coalfield.
(2) The contents, bioaccumulation, effect factors and relationships with soil characteristics of trace elements (As, Cd, Cr, Cu, Ni, Pb and Zn) in earthworms Pheretima guillelmi from the Huainan coal mining area were studied. Cd, Zn and As were relatively bioaccumulated by earthworm. Trace elements in soil were originated from several sources, including agricultural operations, traffic pollutions and geologic origins. The accumulation of elements by earthworms was affected by soil physicochemical properties such as the organic matter, pH, EC, TK and TP. The transfer model of some trace elements from soil to worms could be established by linear regression analysis, developing the potential of earthworms as bioindicators for monitoring metal pollution in soils.
(3) The total contents, speciation and driving factors of trace elements (Co, Cr, Cu, Mn, Ni, Pb and Zn) in soils from the Huaibei mining area were investigated, as well as the mobility and bioavailability of elements. The study area was appropriate for plant growth. Transfer factors of Cu, Pb and Zn from soil to corn grains were relatively high. The results of BCR scheme revealed that the quantity of the mobile fractions of the Mn, Pb and Zn were dominant. The pH and organic matter contents of soil were significant parameters affecting speciation of trace elements in soil samples. Hierarchical cluster analysis indicated that trace elements in the acid soluble and reducible fractions were more available to corn crops. The elevated mobility and bioavailability of Pb in soil are of great concern in this area.
(4) The speciation, sources and ecological risk of trace elements (As, Cd, Cr, Cu, Ni, Pb, and Zn) in sediments from subsidence pools in the Huaibei mining area were analyzed. Metal speciation indicated the highest bioavailability of Cd, with high proportion of the exchangeable fraction. Hierarchical cluster analysis implied that As and Cd were derived from agricultural activities and natural geochemical components, while Cr, Cu, Pb, and Zn may be related to traffic activities and natural sources. However, Ni was mainly originated from natural source. According to enrichment factors, the potential ecological risk assessment (PER) and risk assessment code (RAC), there was a high risk of Cd but a low potential ecological risk for the remained elements in sediments from subsidence pools in the study area.
(5) The present research work summarized the migration and transformation law, bioaccumulation, speciation, input ways, effect factors and environmental risks of trace elements in water, soil, sediments and organisms in the study area, accordingly establishing the model of biogeochemical cycling of trace elements in the supergene environment of Huainan and Huaibei mining areas.
- the Huainan and Huaibei coal mining areas, trace elements, bioaccumulation, speciation, biogeochemical behaviors