Enrichment Regularity And Speciation Of Heavy Metals In Lead-Zinc Mining Area

Environmental problems from exploitation and utilization of lead-zinc mine have received public attention. Speciation and transmission way of heavy metals have a direct impact on the health of local residents. However, it's not clear that how heavy metals migrate from ore into environment and what the media is. It's also need to deeply study the speciation of pollutants and their binding mode with macromolecules.Therefore, in order to reveal migration and transformation law of heavy metals and investigate the relationship between speciation and tolerance of heavy metals, some studies are carried out. Lead-zinc mining area of Nanjing Qixiashan, which has been exploited over50years, is selected as a main study area, and lead-zinc mining area of Zhangbei Caijiaying with less than a decade exploitation and non-mining area around Beijing are selected as reference areas. Many biogeochemical samples are collected. EDXRF and ICP-MS are used to study the characteristics of heavy metals distribution and pollution tracer of lead isotope. Synchrotron radiation XANES and XRF are used to analyze the speciation and micro-distribution of soil and plants in mining area. Affinity column, electrophoresis, and LC-MS/MS are used to study lead-binding protein of plants with high Pb concentration in mining area. Several results from analyses are concluded as below.Studying of different areas, we found that the pollution is mainly distributed in lead-zinc mining area in Nanjing Qixiashan. Lead concentration of water is over the standard value, and concentrations of Pb, As, Cd, and Zn are also over the standard values in soil. Besides, the concentrations of Pb and As are very high.Lead isotope analysis shows that the pollution source is mainly from the mine in Qixiashan, and atmospheric deposition is one of the main pathways of pollution spread over there.Concentrations of heavy metals in biofilm are higher than the ambient water, soil and plants, which confirmed the enrichment function of heavy metals in biofilm.Soil XANES analysis shows that the speciation of lead is lead sulfate and lead nitrate in the surface soil around dressing plant, but mainly organic chloride methyl lead in the underground soil of1.0-1.2m depth in garden. However, soil accumulate arsenic as As(V), no matter the sources of soil from dressing plant, vent, surface or profile soil around mining area. Plant XANES analysis shows that duckweeds accumulate arsenic as As(â…¢) and lead as sulfur-containing organic acid lead. In addition, the lead speciation in cucumber and mosaic shoot growing in lab is different from Pb(NO3)2that was added for cultivation, but is the same with lead speciation of duckweed. There is no difference of lead speciation among roots, stems and leaves of cultivated plants, which preserved lead as sulfur-containing organic acid lead. This result showed that plants are able to transform the inorganic lead into organic lead.Duckweeds from mining area, which is rich in heavy metals, are found the significant distribution of arsenic along veins, and are indentified44lead-binding proteins. There are seven lead-binding proteins of high significance. They are ribulose bisphosphate carboxylase large chain (RuBisCO large subunit), ATP synthase subunit beta, heat shock protein83(HSP83A), heat shock protein81-1(HSP81-1),78kDa glucose-regulated protein homolog (GRP-78),78kDa glucose-regulated protein homolog5(GRP-78-5) and glucose-regulated protein94homolog (GRP-94homolog). Heat shock proteins and glucose-regulated proteins are common metal-binding proteins. However, there is little literature about metal ion binding for RuBisCO large subunit and ATP synthase subunit beta, and there is no literature about lead binding for these two proteins. In addition, there are some amino acid residues of glutamates, aspartates, histidines and methionines in matched peptides for these seven proteins, which were reported to bind with lead easily. Thus, it is suggested that these amino acid residues may play a role for the lead tolerance mechanism of duckweed.In conclusion, with the exploitation and utilization of lead-zinc mine for a long time, the heavy metals of ore are transferred into environment continually. Atmospheric deposition and biofilm play an important role in heavy metals migration on macroscopic and microscopic views respectively. The significant difference of speciation is found between soil and plants. The aquatic duckweed from mining area is not only rich in heavy metals but has significant distribution of arsenic along veins. In addition, there are some ligands binding with lead easily in lead-binding proteins of duckweed. These results and discovery provide a certain reference in understanding the propagation law of heavy metals and exploring the tolerance mechanism of heavy metals in plants.