PB UPTAKE IN COMMON HORSETAIL (EQUISETUM ARVENSE) AT SMELTER IMPACTED ISLANDS IN THE PUGET SOUND

Pb is elevated in Common Horsetail (Equisetum arvense) at smelter impacted islands in Puget Sound. Horsetail, sediment, and surface and pore water samples were collected at eleven stream sites on the islands. Vashon and Maury Islands are located ~8 miles southwest of Seattle, WA and ~2 miles northeast and downwind of the ASARCO copper smelter in Tacoma, WA. Pb concentrations were determined by graphite furnace atomic absorption spectrophotometry (GFAA). Whole plant samples were prepared for analysis using a hot plate nitric acid digestion procedure and sediments were digested with a microwave aqua regia procedure. Pore waters were obtained by centrifuging and filtering (0.45 mm) sediment samples. X-ray diffraction (XRD) was used to determine sediment mineralogy and a Loss on Ignition (LOI) method was used to determine sediment total organic matter (TOM) content.

GFAA results show elevated Pb concentrations up to 60 ppm in plants on both islands. Most surface water sites were below the instrument detection limit (~2 ppb) and pore water Pb concentrations were slightly elevated at some sites (maximum 15 ppb). Stream sediments, composed primarily of quartz, albite, and vermiculite, display elevated Pb concentrations (maximum 302 ppm) and have a TOM content ranging from 2% to 31%.

Pb in the stream water has largely partitioned into sediment since smelter operations ceased in 1985. Pb traveled through the stream channel surface water and was incorporated into the sediment (by cation exchange, sorption, or complexation with organic matter). The current source of Pb in the stream sediment on the islands is erosion from the surrounding soil. Common Horsetail then takes up Pb from the sediment resulting in elevated concentrations and contributing to dynamic biogeochemical cycling in the stream environment.