Current views on EDDS use for ex situ washing of potentially toxic metal contaminated soils

The paper presents a mini-review on EDDS use for ex situ chemical washing of potentially toxic metal contaminated soil. The attention is focused, initially, on studies aimed at verifying the biodegradability and the toxicity of free EDDS and metal-EDDS complexes. Free EDDS is found to be highly biodegradable. Metal-EDDS complexes, instead, are indicated as having variable biodegradability, but their toxicity is found to be always very low. The results obtained during soil washing treatments are successively reviewed. Removal percentages as high as 80–90 % are indicated as maximum obtained values. The extraction process is initially very fast, and then tends to slow down reaching the final equilibrium in about 1 week or even more. Generally acidic conditions are favourable to enhance the process. The influence of organic matter on process efficiency and the interactions between EDDS and soil minerals are also considered, revealing variable effects of the organic matter presence depending on its characteristics, and highlighting the possibility of iron and aluminium washing off during the remediation treatment.