The Study Of Relevance Between Soil Cadmium Pollution And Cadmium Accumulation In Rice

Soil is the basis of human survival, and Cd is a highly toxic heavy metal poisons that can accumulate in the human body through the food chain. Rice is the main food crops of humans, human ingest Cd mainly through rice. So we investigate the correlation between cadmium contaminated soil and enriched cadmium of rice using absorb coefficient, and as a basis for screening the rice-growing areas which have cadmium contamination risks, in order to avoid Cd rice cause harm to humans. In order to meet data privacy requirements and improve ease of use, we establish the research database. We study the difference of the regional absorption coefficient with different scales,such as city, county, town and study the cause differences. We disscusses the ability of four method about Cd available to predict rice Cd content. And we screen the rice-growing areas which have cadmium contamination risks based on avove findings. The main conclusions are as follows:(1) We make a descriptive statistics for the differences of absorption coefficient in different regions, the result shows that city, county, township are moderate and high variability. Analysis of variance of the difference of absorption coefficient in different regions showed that the absorption coefficients in different cities and countries are general significant differences, while in the different towns of the same county this significant differences does not exist. So we can choose the county as a yardstick to determine the area of the absorption coefficient.(2) The most important factors of the difference of absorption coefficients is the pH. As a whole, while the pH increases,the absorption coefficient has a downward trend. When pH is intervals of 0.1, the absorption coefficient between pH 4.8-6.0 is almost no change, but when the pH is 6.0-6.3, decreased mutation point appear. So when the soil pH is less than 6.0, rice Cd absorption coefficient is max and gentle change, when the soil pH is greater than the drop point mutation, absorption coefficient will have a sharp decline, when the soil pH is greater than 7.0, absorption coefficient will be low to mimum.(3) Soil organic matter, texture and type also have influence on the absorption coefficient, but the impact is far less than the soil pH. Under varying degrees of soil contamination, the absorption coefficient decreases with the increasing pollution levels. Soil Zn / Cd also affect the absorption coefficient, the areas with the larger absorption coefficient of soil Zn / Cd is relatively small, and the soil Zn / Cd ratio is greater than rice Zn / Cd ratio. So Zn probably depress rice uptake of Cd and have an effect on the migration and transformation of Cd in rice.(4) Determination methods of effective state, such as DGT, CaCl2 extract can also be used as an important parameter to predict Cd in rice. When the soil has a very low efficiency of Cd, the rice Cd absorption coefficient is significantly lower than the others. When the efficiency of Cd is above a certain value, there are no significant differences between different efficiency of Cd. When lower the pH, soil Cd efficiency have a tendency to rise; when soil pH is greater than 7.0, the soil Cd efficiency decrease to a minimum.(5) In this study, we screened rice-growing areas of Cd risk in Hunan, Guangdong, Zhejiang. The results showed that the level of Cd risk in Hunan Province is higher than in Guangdong, and Guangdong is higher than in Zhejiang. Cd risks is almost all security levels in rice-growing areas of Zhejiang.