Preliminary assessment of time trends in bioavailable metals in the Tri-State lead/zinc mining district through analyses of tree cores

Abstract

The Tri-State mining district in the central U.S. was a major source of zinc and lead from the early 1800s to 1970, producing 11.7 million tons of zinc, and 2.8 million tons of lead. Soils and streams in more than 70 square miles of the mining district and downstream areas are contaminated by metals. Little environmental monitoring was conducted in the district until the late 1970s, when metals-laden water started to flow from the abandoned mines. To retrospectively determine trends in metals bioavailability during unmonitored decades and recent trends in metals, cores extracted from 36 trees distributed throughout the district were analyzed by laser-ablation-inductively-coupled plasma/mass spectroscopy (LA-ICP/MS). Preliminary analyses indicate that most metals concentrations decreased after cessation of mining. Recent reclamation activities appear to have increased the amount of bioavailable metals in the environment, probably through mobilization in air during disturbance and transport of tailings for use as aggregate, or through runoff of newly-available metals-contaminated fine sediments.