Solid phase partitioning of metals in Managed Realignment soils: laboratory studies in timed soil sea-water batch mixtures

Geochemical interactions between agricultural soil and sea-water at a salt marsh restoration Managed Realignment site in Essex, UK were simulated through a series of laboratory experiments. Soil from the site was mixed with sea-water for 0–30 days in batch reactors. The resulting soil residue was subjected to a modified version of the Tessier sequential extraction procedure involving leaching with 5 reagents of progressively increasing strength. Differences in total metals extracted by the series of sequential extractions in comparison to a single digest hindered interpretation of data. Analysis of the sequential extracts and residual sea-water for a suite of metals revealed that Na, Mg and K were sorbed from sea-water to the soils, and from the readily exchangeable fraction of the soil, Ba, Ca, Mn, Ni and Zn were depleted. In the more strongly held fractions extractability of a number of metals, most notably Al, Fe and K by acid leaches was observed to increase as a result of contact with sea-water. The extractability of the heavy metals Cr, Pb, Ni and Zn from these tightly held fractions was also observed to increase as a result of sea-water mixing. However, results imply that tidal inundation of the soils at the site will not result in significant leaching of metals to the environment.