Differential mobilization and metal uptake versus leaching in multimetal soil columns using EDTA and three metal bioaccumulators

Leaching characteristic of potentially toxic metals of artificial soil made from municipal sludge compost

Landscaping of municipal sludge is a good choice to solve the sludge disposal problem, and EDTA treatment can effectively promote the uptake of heavy metals (HMs) by plants, but the heavy metal leaching process and its main control factors are still poorly understood during the sludge landscaping disposal. In this study, the migration behavior of HMs in artificial soil made from municipal sludge compost (MSC) were investigated using soil column experiments. After six leaching events for a total of one year's rainfall, the average reduction percentage of total phosphorus, total nitrogen, organic matter in the MSC artificial soil were 13.4%, 10.1%, and 7.8%, respectively, while those of copper, lead, zinc, cadmium, nickel were 12.9%, 8.37%, 11.5%, 5.94%, and 10.7%, respectively. Treating ethylenediaminetetraacetic acid (EDTA) to the MSC artificial soil further enhanced the leach index of HMs to different degrees. HM concentration in leachate were increased with peak times postponed. Though EDTA treatment increased HM concentrations in subsoil, it did not change their water washing efficiency. The retention of HMs in subsoil was related to properties of local soil and its interaction with leachate. The potential ecological risk was of quite strong risk category in the MSC artificial soil and rapidly decreased from moderate to slight risk in subsoil. Cadmium was the main contribution accounting for 46%-93% of ecological risk. For landscaping applications, the composition of MSC artificial soil and local soil, as well as the capacity of the surrounding water, needs to be considered.

Insights into Heavy Metals Leakage in Chelator-Induced Phytoextraction of Pb- and Tl-Contaminated Soil

Chelators including DTPA (diethylene triamine pentaacetic acid) and oxalic acid were selected for inducing phytoextraction of heavy metals (HMs) from Pb-, Tl-, and Pb-Tl- contaminated soil, in which heavy metals leakage was highly remarkable. Results showed that compared with the control group without chelating agent under planting conditions, the extraction efficiency (i.e., uptake coefficient) of Pb, Tl increased by 86%, 43% from Pb-Tl- contaminated soil in the presence of oxalic acid, and there was no significant change in heavy metal leakage under rainfall conditions. It was the best phytoremediation scheme in this work. Under rainfall conditions, the HMs concentration in the leachate showed a linear decreasing trend. Acid rain promoted the leakage of heavy metals, and the average leached amount of Tl increased by 1.47 times under acid rain conditions. However, for Pb, DTPA was the main influencing factor, followed by acid rain.