Aging factor and its prediction models of chromium ecotoxicity in soils with various properties

Aging of pollutants determines bioavailability and toxicity thresholds of environmental pollutants in soil. However, the ecotoxicity of chromium (Cr) rarely considers the effect of aging as well as soil properties. In order to explore the aging characteristics and establish their quantitative relationship with different soil properties, this study selected 7 soils with different properties through exogenous addition of Cr and determined its toxicity on barley root elongation. From 14d to 540d, EC₁₀ and EC₅₀ of barley root elongation ranged from 21.40 to 312.52 (mg·kg^-1) and 50.15 to 883.88 (mg·kg^-1) respectively. The hormesis appeared in the dose-response curve of acid soil as relative barley root elongation reached >110 % compared with the control. Extended aging time of Cr from 14d to 540d was associated with the attenuation of the toxicity of Cr, as the aging factor increased from 1.26 to 6.09 for EC₅₀, from 0.88 to 4.98 for EC₁₀. The prediction model of AF_EC50 and soil properties is lg (AF_360d) = 0.306lg Clay+0.026lg CEC + 0.240 (R² = 0.872, P < 0.01). The results demonstrated that with the extension of aging time, the toxicity of Cr decreased at 360d and reached a slow reaction stage, after that soil OC, Clay and CEC could well explain the aging procedure of Cr (VI). These results are beneficial for risk assessment of Cr contaminated soils and establishment of a soil environmental quality criteria for Cr.