Recommended risk screening values for Cd in high geological background area of Guangxi, China

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Abstract
Because of unusually high cadmium concentrations in the soil, the risk screening values of soil Cd in the existing standard is not applicable to the Cd high geological background areas. The aim of our study is to explore recommended risk screening values applicable for Cd high geological background areas of Guangxi, China, to help locals with land management and guarantee the quality and safety of crops as well as providing the theoretical basis for guiding the production safety. A total of 903 pairs of rice samples and root soil samples were collected. The Cd concentration of soil-rice samples and soil pH were determined. The scatter diagram method was used to gradually increase the screening values, and the value with the most samples in the correct interval was counted as the recommended risk screening value. The soil Cd concentrations ranged from 0.06 to 7.08 mg·kg−1 and the rice Cd ranged from 0.002 to 1.488 mg·kg−1; 64.89% of soil samples exceed the RSVs and 27.8% of rice samples exceed the allowable limit of Cd. The recommended risk screening values of Cd in study area were 0.5, 0.7, 1.5, and 2.4 mg·kg−1 for soil with pH ≤ 5.5, 5.5 < pH ≤ 6.5, 6.5 < pH ≤ 7.5, and pH > 7.5, respectively. Compared with the standard screening value, the accuracy of using the recommended screening value as the reference value to judge whether the Cd concentration in rice exceeds the standard was increased by 12%, 20%, 21%, and 47%, respectively. The recommended screening value can be used as the standard value to better indicate the soil environmental quality in the study area.

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