Distribution Of Heavy Metals In The Soil-rice System Of The Western Of Hainan

In this study, applying the methods of combining the field investigation and indoor analysis, and with the aid of geostatistics and GIS spatial analysis tools, with heavy metals lead and cadmium, zinc and copper as an example. To research the heavy metals contents distribution in the soil-rice system of the western of Hainan. Reveal its distribution characteristics of heavy metal pollution in the study area and ecological risk assessment, discuss the main influence factors of heavy metals concentrations distribution, provide the basis for rice production safety, protection of ecological environment of Hainan tropical agricultural production to provide a reference. The main conclusions are as follows:1. The concentrations of cadmium, copper and zinc in the top soil (0-20cm) of arable land in western Hainan were lower than the maximum limit levels of China’s Environmental Quality Standard for Soils. The soil is in clean level. Soil lead content slightly higher than the standard limit content of lead. The average concentrations of soil lead, cadmium, copper and zinc were:43.58,0.087,9.81and24.86mg kg-1, respectively. The Igeo values of the heavy metals in soil below1, the ecological risk of them were lower.2. The spatial distribution of soil lead, cadmium, copper and zinc are mainly determined by the distribution of soil parent materials. The concentrations of copper and zinc in northern part of study area, which are Pyroclastic distribution area, are relatively higher than other areas, which are45.92and66.18mg kg-1, respectively. The soil lead concentration of Fluvial distribution area is highest, which is51.40mg kg-1.3. The contents of lead, copper and zinc in different layers differ significantly. As a whole, the trace elements are tended to accumulate in top layer than parent materials, and this indicated of existence of out-sourced contamination.4. The concentration of DTPA-Cu and DTPA-Zn are7.11and6.28mg kg-1, respectively. Effective copper content in soil positive correlated with total copper concentration and copper activation rate is affected by soil pH. Soil available zinc content and total zinc content relationship is not significant, but with soil organic matter and nitrogen content were positively correlated.5. The concentrations lead, cadmium, copper and zinc in polished rice are0.14,0.11,5.68and15.77mg kg-1, respectively. And the trace elements in rice straw are higher than polished rice. The concentrations of lead and cadmium in several samples are higher than the maximum limit standard of China. However, the assessing results of single factor pollution index indicate that the contents of lead and cadmium in polished rice are clean.6. The concentration of lead in polished rice is positively correlated with the soil CEC, and the regression equation is CPb=0.008X CEC+0.016(R2=0.579). The contents of other trace elements in polished rice are no significant relationship with the soil CEC, orgmatic matters content and other soil properties.7. The concentrations of copper and zinc in polished rice positively correlatied with the contents of them in soil. The accumulation coefficients of copper and zinc in polished rice decrease with the increase of copper and zinc contents in soil. Soil acidification, to some extent, stimulates the absorption of Cu. In the area of volcanic debris materials where the Cu content is higher, the use of alkaline fertilizers are recommended to prevent pollution of rice by Cu as a result of soil acidification.