Derivation Of Cd Safety Threshold And Establishment Of Bioaccumulation Prediction Model In Typical Paddy Soil Of Jiangsu Province

The current Soil Environmental Quality Standard(GB15618-1995)unified China's soil environmental quality standards for the first time.Since its implementation,the standard has made a certain contribution to the assessment of soil environmental quality.However,many deficiencies of the standard have gradually emerged over time.The standard did not fully consider in the great differences of soil properties and rice cultivars.Therefore,the scientificity of the standard still needs to be improved.Rice is the main food crop in China.Compared with other crops,rice is more capable of accumulating cadmium(Cd)from soil.Therefore,the study on the environmental quality standard of soil Cd in rice producing area provides important reference for the safety evaluation of rice in the region.In this study:1.Twelve rice cultivars widely grown in Jiangsu Province were selected,and two representative paddy soils(acid soil sampled from Xinghua City and neutral soil sampled from Changshu City)with different physicochemical properties were collected from Jiangsu Province.The greenhouse pot experiments were used to study the sensitivity differences of accumulation ability of different rice cultivars,and different water management models were set up to study the effects of soil moisture conditions on Cd uptake by grain.2.The safety thresholds of Cd in two typical paddy soils of Jiangsu Province was derived based on species sensitivity distribution.3.Ten soils covering a wide range of soil properties were collected from throughout Jiangsu to identify the major controlling factors and develop prediction models for Cd transfer and bioaccumulation from soil to rice.4.Continuous EDTA extraction method was used to extract the available Cd in the soil,combined with the available Cd and soil properties to construct the prediction equation of exogenous Cd content thereby reducing errors caused by different sources of soil contamination.The main results are as follows:(1)There were significant differences in Cd concentrations in brown rice due to the difference of enrichment ability,the highest is 5 times higher than the minimum content,and the indica hybrid rice was significantly higher than that of japonica regular rice and japonica hybrid rice.Different water management models had a significant effect on Cd accumulation,and the Cd content of grain in alternate wetting and drying conditions was significantly higher than that under flooded conditions.(2)The SSD curves for Cd were fitted with Burr ? type distribution based on the bioconcentration factor of the twelve rice cultivars.The 5%hazardous contents were then derived inversely by the national food safety standard.The threshold value based on total Cd content in the Xinghua soil and the Changshu soil were 0.78 and 1.17 mg·kg-1 respectively.The corresponding threshold value based on CaC12 extractable Cd were 0.13 and 0.14 mg·kg-1.The corresponding threshold value based on EDTA extractable Cd were 0.46 and 0.64 mg·kg-1.The Cd thresholds based on total Cd in the soils were higher than the second grade(0.3mg·kg-1 for soils with pH<7.5)of the current Chinese Soil Environmental Quality Standard(GB15618-1995).(3)The results of stepwise multiple liner regression analysis showed that pH and organic carbon(OC)were the two main variables contributing to rice Cd content except soil total Cd.The regression equation based on soil total Cd,pH and OC could well predict Cd in brown rice in different soils,with a correlation coefficient of up to 0.90.(4)Multiple regression analysis was used to quantify the relationship between soil extractable Cd content and exogenous Cd content.It was found that the concentration of extractable Cd after secondary EDTA extraction combined with soil properties can better predict exogenous Cd content.