TRACKING LONG-DISTANCE DEPOSITION AND ASSIMILATION OF AIRBORNE SMELTER EMISSIONS IN NORTHEASTERN WASHINGTON LAKES USING LEAD ISOTOPE ANALYSIS

Abstract

Metal pollution from mining and smelting operations into aquatic ecosystems can cause long-term biological impacts. Several studies have addressed the biological effects of both direct discharge of mining slag and diffuse atmospheric metal deposition into freshwater environments near metallurgic facilities. The upper Columbia River valley is highly contaminated with trace metal waste from nearby smelting operations in Trail, British Columbia, Canada and Northport, Washington, USA. Previous studies have tracked depositional patterns of emissions from these smelters; however, these studies have focused on lakes within 50 km of the smelting facilities. Additionally, no studies have addressed whether these contaminants are biologically available to aquatic organisms. This work analyzed the trace metal concentrations and Pb isotope compositions of sediment cores, sediment grab samples, and zooplankton from remote eastern Washington lakes ranging from 20 to 144 km and 1 to 126 km downwind of the Trail and Le Roi smelters, respectively, to determine possible sources of atmospheric metal deposition in the upper Columbia River valley. Metal deposition and Pb isotope compositions of sediment rapidly changed in a non-linear manner as distance from smelting operations increased. Pb isotope compositions in sediment surface grabs suggest emissions were deposited in lakes 105 km downwind of Trail, and 66 km downwind from Le Roi. Sediment cores provided evidence that the depositional footprint of the Le Roi smelter may stretch as far as 112 km downwind, and emissions from the Trail smelter can be detected 144 km downwind. Changes in zooplankton body burdens and Pb isotope compositions were not as clear as those observed in sediments. Pb isotope compositions of zooplankton suggested legacy smelter contamination in lake sediments were remobilized in anoxic lakes 86 km and 66 km downwind of the Trail and Le Roi smelters, respectively. Cd, Sb and Pb body burdens were highly correlated with Pb isotope compositions in zooplankton suggesting these metals were biologically available from emission fallout in sediment, and were actively assimilated by zooplankton.