Pollutant associations with particulates in stormwater

Many studies have identified metals in urban runoff as a major contributor to the degradation of urban streams and rivers. Metals of most concern are copper, cadmium, chromium, lead, mercury, and zinc. Metals in urban runoff can occur as dissolved, colloidal and particulate-bound species. Therefore, it is important to measure all forms of heavy metals, especially the particulate and filterable fractions, when determining their fate and effects. The objectives of these tests were to determine the associations of heavy metals (along with some major constituents and nutrients) with different-sized particulates using cascade sieves and filters. Sequential extraction experiments were also conducted to examine the treatability and other characteristics of the filterable (<0.45μm) portion of the heavy metals using Chelex-100 resin, UV-light exposure, and Anodic Stripping Voltammetry (ASV). Preliminary results show that total phosphorus and chemical oxygen demand are associated with the particulates and in general decrease with a decrease in particle size. Obviously, concentrations should all decrease with filtration. However, there were periodic jumps in concentrations for some conditions, reflecting variability in the analytical method and the sample handling. Results using ASV show the metals of concern (Zn, Cd, Pb and Cu) all present in the dissolved (<0.45μm) fraction of the stormwater samples with Zn normally present in the highest concentration. Exposure of the samples to UV light increases the concentration of most of the metals, indicating a dissociation of metals from organic complexes or colloids. Sampling and analyses is continuing through April 2005. Sample fractions will be analyzed for Zn, Cd, Pb and Cu using ICP-MS, and the sequential extraction procedures and toxicity tests will be completed. Copyright ASCE 2005.