Environmental Geochemistry Of Cadmium In Soils Of Subsidence Area Guqiao Coal Mine In Huainan

Coal is an important once energy in china and plays a crucial role in the development of the national economy, but in the process of mining, processing and utilization of coal, making for the ground subsidence and accumulation of coal gangue, it had a serious impact to the environment around the mining area, and especially, soil heavy metal pollution has been concerned by many scholars. As we all known, cadmium is one of a toxic element in soil environment. When cadmium contaminant enter in the soil through various channels, it can make crop yield and quality decline, thus endanger human body health through the food chain. In recent years, the pollution of soil cadmium and rice of cadmium exceeding standard badly had been reported repeatedly. Therefore, this study focused on Guqiao coal-mining subsidence. In the basis of full investigation of related scientific literature at home and abroad, through the chemical experiment, precision instrument test and multiple perspectives analysis method, the coal mining subsidence area of cadmium in soil-wheat are analyzed and studied. The main research conclusions are as follows:(1) The average content of total Cd is 0.22 mg/kg, and is 3.67 times of soil background values of Huainan city. Cd has a certain concentration in the soil of research area. The availability Cd by DPTA has a higher proportion in total Cd, So it had strong activity Cd with activation rate to an average of 37.86%.Total Cd and availability Cd were all accumulated in subsoil (0～20 cm) and there was a significant positive correlation between two parts.(2) The different speciation Content of Cd ranked as follows:residual fraction (50.59%)>exchange fraction (23.24%)> Fe-Mn oxide bound fraction (15.77%)>carbonate bound fraction (6.18%)>organic bound fraction (4.22%).Bioavailable Cd (exchangeable) and biological potential Cd (Carbonate bound、Fe-Mn oxide bound、Organic bound) respectively have a possession of 23.24% and 26.17%, it could become availability with the effect of soil environment of mine.(3) The organic matter, total nitrogen, total phosphorus of soil have significantly relation with total Cd and all kinds of speciation Cd, they are the important factors that influence the distribution of these forms Cd. Thus effective control of subsidence basin sewage irrigation, agricultural fertilizer use will help to reduce potential ecological risk of Cd in the farmland soil. The pH has a negative correlation with exchange Cd, and has a significant positive correlation with carbonate bound Cd and Fe-Mn oxide bound Cd, So prevent farmland soil acidification can effectively restrain the transformation of availability Cd from exchange fraction、carbonate bound fraction、Fe-Mn oxide bound fraction.(4) The distribution of Cd in different organs of wheat ranked as follows:root (0.135mg/kg)>stem and leaf (0.074mg/kg)>grain (0.041mg/kg). The mean concentration of Cd in grain was lower than the national food hygiene standard. The bioaccumulation factors of Cd in different organs of wheat all below 1. The translocation factors of root to stem and leaf or stem and leaf to grain are litter more than 0.5, translocation factors of root to grain is lower than 0.5. Indicates that it has a certain extent absorbing ability by the study area of wheat, but the migration ability of Cd which from wheat root part to the ground or the ground between is weak.(5) There have a linear relationship between total Cd and different organs of wheat of Cd, also between availability Cd and different organs of wheat of Cd. So it has a good reference value to the forecast research of farmland Cd content in soil-wheat system. The content of Cd in different organs of wheat have relatively significant correlation with carbonate combined Cd and Fe-Mn oxide state Cd, and the rest of the three forms that there was no significant correlation, it shows that carbonate combined Cd and Fe-Mn oxide state Cd have important affection in up taking soil Cd by wheat.(6) Based on the calculation results of potential ecological risk index and health risk assessment, the potential ecological risk of Cd in soil reached the strong ecological risk levels, the health risk of Cd to the individual person per year were at 2.54×10-5 a-1, which was lower than the maximum allowance levels recommended by the International Commission on Radiological Protection (ICRP)(5×10-5,a-1), but the value was higher than the maximum allowance levels by ICRP at some points, so the pollution of Cd in soil-wheat should be paid more attention.