Keywords: 
• soil /
• copper /
• phytotoxicity /
• bok choy

Abstract: The phytotoxicity/bioavailability of copper(Cu) in soil mainly depends on its liable portion in soil solution and the soil solution properties.Determination of the phytotoxicity of soil soluble copper as a function of soil solution properties is helpful to develop soil environmental risk assessment guidance for China.The bioassay of bok choy plant growth was performed in 17 representative Chinese agricultural soils to investigate the phytotoxicity of soluble Cu based on soil pore water and CaCl₂ extraction in order to develop empirical models for predicting the soluble Cu phytotoxicity.When considering the toxicity thresholds for Cu in soil pore water,it was found that the effective concentrations that caused 10% biomass growth inhibition(EC₁₀)and 50% inhibition(EC₅₀) represented 14.7 to 14.6 fold differences between the maximum and minimum values.Similarly,the EC₁₀ and EC₅₀ values of Cu extracted by 0.01 mol·L^-1 CaCL,had 12.7 to 7.7 fold differences,respectively.These results suggested that the toxicity thresholds of soluble Cu were greatly affected by soil solution properties in a wide range of soils.Meanwhile,the relationships were developed between the important soil solution properties(dissolved organic carbon(DOC),pH,electrical conductivity(EC),S,Ca²⁺,Mg²⁺,K⁺and Na⁺) and the toxicity thresholds for Cu in a wide range of soils,which indicated that the soluble Cu toxicity on bok choy was predicted well by soil solution properties.Moreover,the multiple regression results showed that Mg,K and S in soil pore water were more important factors controlling Cu toxicity.Single S or K was found to explain 34% (EC₁₀) or 26% (EC₅₀) of variance of the toxicity thresholds,respectively.These quantitative relationships between soluble Cu toxicity and soil solution properties can be helpful for soluble Cu toxicity risk assessment of terrestrial environment.