Geochemistry Characteristic Of Heavy Mental In Soil-Crop System In Typical Area Of Yangtze River Delta

Recently, environment pollution due to rapid developments of industry in the Yangtze River Delta has aroused a lot of public concern. Specifically, heavy metal pollution in croplands is the key issue since rice and wheat from croplands are the main food sources of local residents. Thus, it is critical to do a comprehensive survey on heavy metal pollution in croplands of Yangtze River Delta. However, the traditional geochemical methods widely used in heavy metal pollution survey are very time-consuming and money-consuming. It is therefore necessary to develop a rapid and simple way to do in situ monitoring of cropland pollution. Soil spectroscopy reflects a lot of chemical characteristics of soils and may be potentially used in monitoring cropland pollution through remote sensing.In this thesis,66groups of rice-soil samples (including rice and underneath soils) and88groups of wheat-soil samples (including wheat and underneath soils)were sampled from croplands of Zhenjiang, Changzhou, Suzhou, Wuxi, Taizhou, Yangzhou, Nantong and Shanghai. Then concentration of heavy metals and major elements, soil pH, total organic carbon and spectroscopy of those samples were measured. After detailed analysis and discussion, we reached the following conclusions:1) Soils and plants in the Yangtze River Delta have already been affected by heavy metals. Rice soils and wheat soils are polluted by Cd. According to Standard GB15618-1995-Ⅱ,9.09%of the rice soils exceed the standard level for Cd and most of the polluted samples are from Suzhou, Zhenjiang and Changzhou. Also,10.23%of the wheat soils exceed the standard level for Cd and most of the polluted samples come from Suzhou and riverside area. In addition, according to Standard GB2762-2005, rice grains exceed the standard level for As and Cd by25.76%and4.55%, respectively. Most of the As-polluted rice grain samples are from Changzhou, Suzhou, Taizhou and Yangzhou while most of the Cd-polluted rice grain samples come from Suzhou and Wuxi. Wheat grains are also enriched in Cd, Cu, and Zn by7.95%,7.95%and17.05%, respectively. Most of the polluted wheat grains were found in Suzhou, Wuxi and riverside area.2) Among the seven heavy metals:As, Hg, Pb, Cd, Cr, Cu, and Zn, it is the easiest to accumulate Cd while the most difficult to assimilate Cr for rice. Similarly, wheat tends to assimilate Cd, Cu, and Zn but reject Cr.There are mainly two factors that would affect accumulation of heavy metals in plants:bioavailability ratio of heavy metals as well as physical and chemical characteristics of soils. The higher the bioavailability ratio of heavy metals, the easier the accumulation of heavy metals in plants. High concentration of Al2O3, Fe2O3and TOC in soils can limit accumulation of certain heavy metals in plants. For example, high concentration of Al2O3and FeaO3in soils could limit assimilation of As, Cr and Zn by plants while high TOC in soils could limit enrichment of Hg and Zn in plants. High concentration of Fe2O3and TOC in soils could also suppress accumulation of Pb in rice. In contrast, soil pH and CaO concentration are the dominant factors limiting accumulation of Pb in wheat. In addition, high soil pH and concentration of CaO, MgO and P in soils would make it difficult for plants to enrich Cd and Cu.3) Soil pH showed a positive correlation with soil reflectivity in visible wavelength. Spectroscopy-predicted soil pH and in situ measured soil pH showed a correlation coefficient of0.7245(n=154) and0.7148(n=154) for rice and wheat, respectively. Based on this model, we made a relatively good prediction for293soil samples from Suzhou, Wuxi, and Shanghai. In detail, spectroscopy reflectivity made a better prediction than the first derivative of spectroscopy.In addition, soil TOC showed a significant negative correlation with soil reflectivity in the wavelength between550nm and2300nm. This reflectivity-predicte -d soil TOC mirrored measured soil TOC quite well with a correlation coefficient of0.8498. Soil Cr and Cu also showed a negative correlation with soil reflectivity in the wavelength between1400nm and2300nm and predicted values correlate measured values with R2of0.8383and0.6199for Cr and Cu, respectively.