Predicting spatial and temporal variation of Cd concentration in rice grains in the Lower Changjiang Plain during 2004-2014 based on soil geochemical survey data with GIS

The Lower Changjiang Plain (LCP) is one of the most important regions for rice production in China. A significant increase of soil Cd concentration (Cd-soil) with the decrease of soil pH has been found during the recent decade (2004-2014) on the regional scale. In order to evaluate the effects of the changing soil parameters on Cd concentrations in rice products, a linear mixed model was built to relate the carefully selected soil parameters to Cd concentration in rice grains (Cd-rice) with the random component modelled as a spatially correlated random variable. With the 2004 soil geochemical survey data, and the 2014 soil monitoring data, spatial and temporal variation of Cd-rice was predicted in Geographical Information System (GIS) with the model. It was found that although the predicted Cd-rice in 2014 is still under the food standard limitation of 200 mu g/kg, it has increased significantly (p < 0.001) over this decade, with the median increased from 19.06 mu g/kg in 2004 to 24.11 mu g/kg (in dry weight basis) in 2014. The result also showed that the spatial patterns of Cd-rice did not coincide with those of the soil pollution levels calculated from the environmental quality standard of China (GB15618-1995), which implies that the traditional soil Cd pollution assessment needs to be improved with more consideration of its bio-availability.