Possibility of Predicting Heavy-Metal Contents in Rice Grains Based on DTPA-Extracted Levels in Soil

Abstract

The heavy-metal contamination in soils has posed a potential threat to safe crop production in China as well as worldwide. It is essential to make a correct evaluation of the contaminated status of soil prior to adopting the special strategies for controlling or alleviating the contamination of crop products. In this study, a large collection of rice and soil samples were taken from diverse locations of Zhejiang, China, and heavy-metal contents were analyzed. The results showed that there was a large difference in heavy-metal contents in soil (diethylene triamine pentaacetic acid [DTPA]-extractable) and in rice grain. Approximately 34.3% of rice samples had cadmium (Cd) levels above the allowable maximum values (AMV) of 0.1 mg/kg and 5.7% had chromium (Cr) levels above the AMV of 1.0 mg/kg. No sample had unsafe levels of nickel (Ni), arsenic (As), copper (Cu), or zinc (Zn). This indicates a major issue for safe rice production with respect to Cd and Cr contamination. Low soil pH leads to an increased availability of As, Cd, Ni, and iron (Fe) for plants, but this has less affect on Cr and Cu levels. The association of grain heavy-metal content with soil DTPA-extracted levels is well described by linear regression models. However, the fits of these regression equations (predicted by R 2 values) varied with each heavy metal. While regressions based on the pooled data from several cultivars adequately predicted rice-grain heavy-metal levels, better fits were obtained when cultivar-special regressions models were used.