Soil washing by biodegradable GLDA and PASP: Effects on metals removal efficiency, distribution, leachability, bioaccessibility, environmental risk and soil properties

Washing is one of the most practical remediation methods for heavy metals contaminated soil, however, conventional washing agents always cause soil acidification and salinization and bring about other negative impacts on soil microbes and plants. This study selected glutamate-N,N-diacetic (GLDA) and polyaspartic (PASP) as biodegradable chelators to remove Cd, Pb and Zn from contaminated farmland soil. The residual metals’ leachability , bioaccessibility , environmental risk and the properties of the soil were investigated after the polluted soil was washed with GLDA and PASP. Results showed that 93.8% of Cd, 87.9% of Pb and 91.9% of Zn were washed out when the concentration of GLDA was 50 mmol/L, pH was 5.5, S/L ratio was 1:10 and contact time was 90 min. Meanwhile, compared with the original soil, the leachability and bioaccessibility of the residual metals were decreased and the stability was increased after washing by GLDA or PASP. The environmental risks of metals were decreased as well by decreasing their bioaccessible concentrations. Moreover, the activity of the soil enzyme was improved after leaching. To sum up, this study provided a theoretical and scientific basis for the treatment of soil heavy metals pollution with biodegradable chelator.