Ecotoxicity of Hexavalent Chromium [cr (VI)] in Soil Presents Predominate Threats to Agricultural Production with the Increase of Soil Cr Contamination

The relative severity between chromium (Cr)-mediated ecotoxicity and its bioaccumulation has rarely been compared and evaluated. This study employed pot incubation experiments to simulate the soil environment with increased Cr pollution and study their effects on the growth of crops, including pepper, lettuce, wheat, and rice. Results showed that increasing total Cr presented ascendant ecotoxicity in upland soils when pH > 7.5, and significantly reduced the yield of pepper, lettuce and wheat grain by 0.3-100 %, whereas, this effect was weakened even reversed as the pH decreased. Surprisingly, a series of soils with Cr concentration of 22.7-623.5 mg kg(-1) did not cause Cr accumulation in four crops over the Chinese permissible limit. The toxicity of Cr was highly associated with extractable Cr, where Cr (VI) made the greater contributions than Cr (III). Conclusively, the ecotoxicity of Cr poses a greater environmental issue as compared to the bioaccumulation of Cr in crops in upland soils, while extractable Cr (VI) makes the predominant contributions to the ecotoxicity of Cr as the total Cr increased. Our study proposes a synchronous consideration involving total Cr and Cr (VI) as the theoretical basis to establish a more reliable soil quality standard for safe production in China.