Environment materials (humic acid (HA), super absorbent polymers (SAP), fly ash (FM) and zeolite (FS)) were used as amendments to immobilize heavy metal Pb and Cd in artificial contaminated soils. The results showed that soil pH and EC changed after the application of single or combined and co-application amendments. The leaching Pb in the single-Pb contaminated soils amended with HA, FM, C1 (HA, SAP, FM, FS) and C2 (HA, SAP, FM) were 93%, 87%, 59% and 77% of the control without amendments, respectively. The leaching Cd in the single-Cd contaminated soils amended with SAP and C3 (HA, SAP, FS) were 64%, and 83% of the control, respectively, in four-steps leaching. The leaching Pb in the Pb-Cd co-contaminated soil amended with HA, C2 and C3 were 41%, 95% and 77% of the control, respectively. The leaching Cd in the Pb-Cd co-contaminated soil amended with HA, SAP and C3 were 85%, 72% and 55% of the control, respectively. The results indicated that C1 and SAP was the best amendments for single Pb and Cd contaminated soil, respectively. While the combined amendment, HA and C3 could prevent Pb and Cd to be leached from co-contaminated soils, respectively.
Nickel (Ni) is an essential element for plants but it is toxic at large concentrations. In the present study, bioassays of bok choy were taken in 17 Chinese soils with different properties and climate characteristics to evaluate the toxicity of soil soluble nickel (Ni) toxicity in soil pore water to bok choy. The tested soils were spiked with 8 levels of soluble Ni chloride with or without leaching treatments. The effective soluble Ni concentrations that caused 10% root growth inhibition (EC10) and 50% inhibition (EC50) varied widely from 0.05 to 2.1 mg/L and from 0.13 to 7.6 mg/L in 17 unleached soils, represented 41.8 to 58.5 folds differences, and from 0.08 to 2.2 mg/L and from 0.47 to 4.5 mg/L in leached soils, represented 27 to 9.6 folds differences. It indicated that the soil soluble properties greatly influenced Ni toxicity to bok choy. However, soluble Ni toxicity thresholds were not significantly decreased in 15 soils. Regression models between soil solution properties and phytotoxicity threshold values were developed. The model showed that soil solution Mg2+K+and electrical conductivity (EC) were the important factors affecting Ni toxicity on bok choy, and meanwhile they were positively related to the toxicity thresholds. These quantitative relationships could be used for the risk assessment of Ni in terrestrial environment in China.
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