Degradation of Lindane by Zero-Valent Iron Nanoparticles

Thus far, zero-valent iron has been studied mostly for the degradation of structurally simple one- and two-carbon halogenated organic contaminants such as chlorinated methanes, ethanes, and ethenes. In this research, laboratory synthesized particles of nanoscale iron were explored to degrade lindane, also known as $\gamma$ -hexachlorocyclohexane, a formerly widely utilized pesticide and well-documented persistent organic pollutant. In general, lindane disappeared from aqueous solution within $24\mathrm{h}$ in the presence of nanoiron concentrations ranging from $0.015\text{to}0.39\mathrm{g}∕\mathrm{L}$ . By comparison, approximately 40% of the initial lindane dose remained in solution after $24\mathrm{h}$ in the presence of $0.53\mathrm{g}∕\mathrm{L}$ of larger microscale iron particles. However, the surface area normalized first-order rate constants were all within the same order of magnitude regardless of dose or iron type. A key reaction intermediate, $\gamma$ -3,4,5,6-tetrachlorocyclohexene from dihaloelimination of lindane was identified and quantified. Trace levels of additional degradation products including benzene and biphenyl were detected but only in the high concentration experiments conducted in 50% ethanol. While up to 80% of the chlorine from the lindane molecules ended as chloride in water, only 38% of the expected chloride concentration was observed for the microscale iron experiment. This work together with previous published studies on the degradation of polychlorinated biphenyl, chlorinated benzenes, and phenols suggest that zero-valent iron nanoparticles can be effective in the treatment of more structurally complex and environmentally persistent organic pollutants such as lindane.