HEAVY METAL CONTAMINATION IN URBAN SOILS

Urban soils may be contaminated with heavy metals due to historical and current use of fertilizers, pesticides, wood preservatives, and construction materials. To examine the distribution of trace metals from natural and anthropogenic sources, we focused on a residential area in Spokane, Washington which has been developed since the late 1800s, and is known to have contained orchards, lumber yards, railcar systems, and dumping grounds, but it is not registered as an action site by the EPA.

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.