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 (<0.45 µm) 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.

Many studies have identified metals in urban runoff as a major contributor to the degradation of urban streams and rivers. Metals of most concern may include copper, cadmium, chromium, lead, and zinc, amongst others. 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 selected major constituents and nutrients) with different-sized particulates in stormwater. The binding strengths of these metals to the particulates were also examined by using a sequential extraction procedure using different acids and bases under several pH values. Also, experiments to determine the relative amount of ionic forms vs. organo-metallic complexes of the filterable (<0.45um) portion of the heavy metals were also conducted.Results show that most of the total phosphorus and phosphate are associated with the particulates, while other nutrients (such as nitrate) are dissolved and their concentrations are not effectively reduced by removing particulates from the stormwater. Obviously, particulate-bound pollutant concentrations should all decrease with filtration through finer sieves. However, there were infrequent jumps in concentrations for some conditions, reflecting variability in the analytical method and the sample handling. Constituents that did not change significantly with filtration included nitrate and sodium, as expected. Other analytes (COD and cadmium) also had little change, except for a single sample in each case. Most of the analytes (turbidity, phosphorus, phosphate, magnesium, chromium, copper, iron, lead, and zinc) had large decreases with filtration, especially for the more contaminated samples. Total solids and COD had much smaller changes with filtration, with substantial fractions associated with the filterable (<0.45 µm) fraction. In many cases (especially for solids), there were major differences in sample characteristics for the set of samples collected from source runoff areas compared to the sample set collected from stormwater outfalls. The larger particulates made up a much larger fraction of the total solids for the source area samples than for the outfall samples, reflecting poor delivery of the large particulates through the conventional drainage systems.Samples were also subjected to heavy metal leaching tests under different acidic conditions. The major constituents (calcium, potassium and sodium) had very little change for any pH exposure condition. Only small fractions of the iron were released under the strongest pH conditions of the exposure tests for all samples, indicating that iron was always strongly bound. These tests indicate that the heavy metals of concern remain strongly bound to the particulates during long WEFTEC ® 2003 exposures at the extreme range of pH conditions likely to occur in urban receiving water s...

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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 (<0.45 µm) 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.

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