Remediation of arsenic contaminated soils by iron-oxide application, evaluated in terms of plant productivity, arsenic and phytotoxic metal uptake

Four iron-bearing additives, selected for known or potential ability to adsorb anions, were evaluated for their effectiveness in attenuation of arsenic (As) in three soils with different sources of contamination (canal dredgings, coal fly ash deposits, and low-level alkali waste). Amendments used were lime, goethite (α-FeOOH) (crystallised iron oxide) and three iron-bearing additives, iron grit and iron (II) and (III) sulphates plus lime, which result in ‘de novo’ iron oxide formation in soils. Each was applied to the test soils at a rate of 1% w/w. A series of plant growth trials were conducted on the equilibrated, amended soils using spinach (Spinacia oleracea) and tomato (Lycopersicon esculentum) as test crops. These were grown in the contaminated soils for a period of three months in controlled glasshouse conditions. Evaluation of the potential of the amendments as immobilising agents was determined by plant growth (biomass) and elemental accumulation in plant tissues, indicating the bioavailability of As and other heavy metals following amendment. Goethite produced the most promising results in terms of reduction of plant shoot As content. It was concluded that, whilst Fe-oxides may be used as effective in situ amendments to attenuate As in soils by reducing its bioavailability, their effects on plant growth require careful consideration. In addition, soil-plant transfer of As was not completely halted by any amendment.