Sediment washing is a relatively simple, typically ex situ technique involving the cleaning of contaminated soils with various reagents. Depending on the nature of the contaminant, a number of additives can be employed in the washing process including acid washing (e. g. H2SO4 and HNO3) and chela­ting agents [e. g. EDTA, diethylenetriaminepentaacetic acid (DTPA) and ethylenediamine-N, N’-disuccinic acid (EDDS)] to assist with the solubilisation and desorption of the metal from the sediment. This technique is useful for weaker bound metals, those associated with the exchangeable, carbonate and reducible oxide fractions of the soil, but is inefficient at removing metals in the residual fraction.93 Acid washing can be applied through a variety of abiotic and biological ex situ techniques.70,94 Chelating agents can be used in soil washing to remove contaminants from sediments through the formation of stable metal chelate complexes which can then be removed in solution.95 EDTA has been studied extensively for use as a chelating agent for use in soil

washing96,97 and can enhance metal mobilisation via two mechanisms: fast thermodynamically favourable complexation between EDTA and certain cationic metals, as well as slow driven EDTA-dissolution. The former involves the breakdown of some weak soil-metal bonds while the latter can partially disrupt the soil structure thus mobilising metals bound to oxides and organics.98