Evaluation of a customized reactive nanoscale-zero-valent iron and zeolite thin capping blend for enhancing natural recovery of wetlands impacted by contaminated legacy gold mine tailings

Abstract

Abstract Legacy gold mine tailings from the 1800’s in Nova Scotia, Canada have elevated mercury (Hg) and arsenic (As) concentrations. Tailings, were slurried into wetlands without treatment. Over a century later, those impacted wetlands are still at risk and innovative in-situ treatment approaches to support natural biological and chemical recovery are needed. Here we report results of our proof-of-concept laboratory study with a customized reactive thin layer capping to limit mobility, bioaccumulation and toxicity of Hg and As in wetland sediment impacted by legacy tailings. The customized reactive amendment is a blend of NANOFER STAR nanoscale zero valent iron (nZVI) and fine-grained zeolite (clinoptilolite) inserted either below, or within a thin cap (silica sand, bentonite and zeolite) and placed over contaminated wetland sediments in beakers. Due to the high concentrations of Hg and As in sediments, invertebrates (Hyalella azteca, Daphnia magna and Caridina multidente) exposed to untreated wetland sediment exhibited high mortality and bioaccumulation of Hg. The reactive capping applications improved the survival of H. azteca and D. magna similar to the survival rates seen in our clean control sediment. Bioaccumulation of Hg was also reduced in C. multidente exposed to the treated sediment compared to the untreated sediment. Furthermore, total [Hg] and [As] in the overlaying water of treated contaminated sediments were reduced by 88% and 99% respectively. Our proof-of-concept testing of this reactive capping blend shows potential for managing and supporting natural recovery of wetlands impacted by historical gold-mine tailings.