Remediating dinoseb-contaminated soil with zerovalent iron

Dinoseb, a dinitroherbicide, was once commonly used in aerial crop dusting of agronomic crops in the western United States. Widespread use combined with improper disposal practices at rural air strips has contaminated numerous sites. Our objective was to determine if zerovalent iron (Fe⁰) could remediate dinoseb-contaminated soil. This was accomplished by conducting a series of batch experiments where we first determined if Fe⁰ could remove dinoseb in aqueous solutions, then in contaminated soil slurries, and finally, in unsaturated soil microcosms (25 °C, θ_g = 0.30 kg H₂O kg^-1). Results showed quantitative dinoseb removal in the presence of Fe⁰ in all three media (aqueous solutions, soil slurries, moist soils) and that removal increased by including either ferrous or aluminum sulfate with the iron treatment. Incubating contaminated soils with Fe⁰ or Fe⁰ plus salts (FeSO₄ or Al₂(SO₄)₃) resulted in 100% removal of dinoseb within 7 d. Liquid chromatography/mass spectrometry (LC/MS) analysis of degradation products showed the transformations imposed by the iron treatments were reduction of one or both nitro groups to amino groups. These amino degradation products were further transformed to quinonimine and benzoquinone and did not persist. These results support the use of zerovalent iron for on-site treatment of dinoseb-contaminated soil.