Effects of Oxidation-Reduction Conditions and Selected Soil Amendments on the Solubility, Mobility, and Phytoavailability of Arsenic in Two High-Arsenic Soils in Hawaii

Abstract

In Hawai‘i, arsenic (As) is present in significant amounts in some soils due to past use of arsenical herbicides and pesticides. Soil physical properties and oxidation-reduction conditions strongly control the solubility and mobility of As, affecting leaching into ground and surface waters, plant uptake, and bioaccessibility. The solubility, phytoavailability, and mobility of arsenic under greater reducing conditions was investigated for two Hawai‘i soils high in As, an Ola‘a Andisol and Leilehua Ultisol. In an incubation experiment, solution arsenic and iron concentrations varied widely, and did not vary significantly according to soil, treatment, redox potential, pH, or time of incubation. Experimental error or microbial populations may have been responsible for the inconsistent concentrations measured. In an experiment assessing phytoavailability, watercress (Nasturtium officinale) grown in flooded soils high in arsenic contained significant amounts of As in the edible tissues. A leaching column experiment examined the effects of vermicompost, rock phosphate, and FeSO4 with lime on the mobility of As in a Leilehua Ultisol. Addition of rock phosphate and vermicompost increased solution As concentration compared to the control, while addition of FeSO4 with lime decreased solution As concentration.