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 μg/kg, it has increased significantly (p < 0.001) over this decade, with the median increased from 19.06 μg/kg in 2004 to 24.11 μg/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.