Screening of Low-Cd-accumulating Rice Varieties and Derivation of Soil Cd Safety Threshold in Southern Jiangsu

There are urgent requirements to solve the problem of cadmium (Cd) pollution in farmlands and rice. With the rapid economic development in Southern Jiangsu, Cd pollution in soil and rice caused by industrialization has significantly increased. The purpose of this study was to screen low-Cd-accumulating rice varieties from main cultivated varieties in Southern Jiangsu, and to deduce the local soil Cd threshold for the safe production of rice. In this study, field plot experiments and field investigation were conducted at different sites and years. Eighteen local main cultivated rice varieties in Southern Jiangsu were selected, including 15 Japonica conventional varieties: Wuyunjing 30 (WYJ30), Suxiangjing 100 (SXJ100), Changnongjing 10 (CNJ10), Nanjing 3908 (NJ3908), Nanjing 5055 (NJ5055), Changnongjing 12 (CNJ12), Nanjing 46 (NJ46), Changnongjing 11 (CNJ11), Jiahua 1 (JH1), Changxiangjing 1813 (CXJ1813), Changnongjing 8 (CNJ8), Wukejing 7375 (WKJ7375), Zaoxiangjing 1 (ZXJ1), Yangyujing 3 (YYJ3), Zhennuo 19 (ZN19), and 3 Japonica three-line hybrid varieties: Changyoujing 6 (CYJ6), Changyou 4 (CY4) and Changyoujing 11 (CYJ11). The differences of Cd bioconcentration factor (BCF) in rice grains among these varieties were comprehensively compared, and the soil Cd safety thresholds at different pH ranges were deduced using the species sensitivity distribution (SSD) method. The results showed that the order of grain Cd accumulation among tested varieties was consistent between field investigation and plot experiments. There were significant differences in Cd BCF among 18 main cultivated rice varieties, with a maximum difference of 4.7 times. The Cd accumulation in some varieties like NJ46 and NJ3908 was stably low. Based on the SSD method, the deduced safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard (0.2 mg·kg-1) (GB 2762-2017) under soil pH 5.0- 6.5, 6.5- 7.5 and 7.5- 8.5 in southern Jiangsu were 0.52, 0.80 and 1.78 mg·kg-1, which were higher than the current risk screening value (GB 15618-2018). It was verified that the deduced thresholds remarkably improved the accuracy of Cd risk prediction of rice in Southern Jiangsu. Based on field plot experiments and field investigation, numerous local main cultivated rice varieties including NJ46 and NJ3908 were screened with stably low Cd accumulation capacity, stable yield and high quality, and therefore are suggested for cultivation in Cd contaminated paddy fields in Southern Jiangsu. The deduced local safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard were higher than the current risk screening value. The results have important implications for the safe utilization of Cd contaminated paddy fields in Southern Jiangsu.