The Use of Plant and Earthworms for Evaluation of Iron-based Remediation of Arsenic Contaminated Soils.

Arsenic is a ubiquitous element found in many minerals all over the world.  In addition to natural deposits, As compounds have been used for hundreds of years as pesticides, herbicides, desiccants, wood preservatives and as a byproduct in mining activities.  With the lowering of drinking water standards for As, there is emergent interest in remediating As contaminated soils.  For a remediation effort to be successful and useful in multiple applications, the remediation must be able to reduce risk of potential leaching and be ecologically beneficial for soil invertebrates and plants.  Re-vegetation of remediated sites is essential for reduction of wind blown particles and soil stabilization.  The objective of this study is to evaluate four iron-containing materials: Fe₂(SO₄)₃, FeCl₃, zero-valence Fe, and Fe-water treatment residual (WTR) for remediation of As (250 mg/kg) contaminated/spiked soils and one slag waste medium.  Multiple pathways were investigated including As extractability (leaching potential), plant phytotoxicity and earthworm toxicity.  All Fe-treatments used in the soils were effective in reducing the most soluble As (pore water and Bray-1 As) thereby reducing the threat of leaching.  The largest decrease in soluble arsenic was in the Fe-WTR treatment.  Pore water As decrease by 98.4% across all media and Bray-1 As decrease by 75.7% across all soils.  There were also improvements in seed germination, shoot elongation and shoot yield across all soils and treatments.  Concentration-response curves establish an IC₂₀ = 40.3 mg/kg Bray-1 As for seed germination and IC₂₀ = 22.0 mg/kg Bray-1 As for shoot yield.  Earthworm arsenic bioaccumulation was decreased in all Fe-treatments in three of the four soils.  The sandy Pratt soil had reduced As body burdens in the Fe-Chloride and Fe-WTR treatments.  In situ treatment of arsenic contaminated soils using Fe-WTR provided the most effective Fe-source to reduce As solubility, improve plant response and reduce bioaccumulation of As by earthworms.