Status of chromium accumulation in agricultural soils across China (1989-2016)

The first national-scale assessment of chromium (Cr) contamination in China's agricultural soils was performed based on 1625 sites analysed with 1799 previously published papers. Spatial and temporal variations were assessed, and the ecological risk was estimated. The range of Cr concentrations in farmland soil is 1.48-820.24 mg/kg. At approximately 4.31% and 0.12% of the sampling sites, Cr concentrations exceeded the screening value (150 mg/kg) and the control value (800 mg/kg), respectively (GB15618-2018). Cr concentrations decreased in the following order: Southwest > Northwest > East > South > Northeast > Central > North China. Moreover, the Cr accumulation rate in agricultural soils may have decreased during 2011-2016, possibly due to government-led changes in China's industrial structure and policies limiting the discharge of polluted industrial wastes. Linear correlations were observed between the application amounts of fertilizers and Cr concentrations in the soil, indicating that the application of nitrogen, phosphorus and potassium fertilizers is an important contributor of Cr in agricultural soils. Additionally, geoaccumulation index (I_geo) values for Cr showed that more than 83.4% of the sampling sites were uncontaminated, with high I_geo values distributed in some areas, especially those with mining and electroplating industries. Overall, this study details the Cr contamination status of agricultural soils in China and provides insights for policymakers enacting measures to prevent pollution.