HEAVY METAL CONTAMINATION IN URBAN SOILS
Topsoil was collected from twenty-five sites (including yards, city parks, and protected urban wetlands that are home to a variety of wildlife and plant species). Soils were leached with 5% nitric acid at room temperature to obtain the more bioavailable fraction, and thermally digested with concentrated nitric acid and hydrogen peroxide according to EPA method 3050B in order to quantify the more weathering-resistant fraction. Both the leaches and the digests were analyzed for trace elements using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). Generally speaking, city parks had lower concentrations of trace elements (arsenic, cadmium, chromium, lead and zinc) than yards. The concentrations of some elements were higher than in the average local soil, and a few homes had arsenic and lead concentrations above Washington State Department of Ecology regulations indicating soil contamination.