Stormwater Heavy Metal Particulate Associations

Abstract

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...

Metals Concentration on Particles in Highway Runoff

“…Sansalone et al, 1996;Characklis et al, 1997;Lau et al, 2009;Helmreich et al, 2010), while others describe particle size distribution (PSD) and the associate metal fractionation within certain size fractions (e.g. Sansalone and Buchberger, 1997;Roger et al, 1998;Morquecho and Pitt, 2003). There are basically two methods of obtaining the particle size distribution: sieving and particle counting devices.…”

Protocol Evaluation of the Total Suspended Solids and Suspended Sediment Concentration Methods: Solid Recovery Efficiency and Application for Stormwater Analysis

“…Particulate-Phase Metal Concentration (M i ). The concentrations of metals associated with particles have been measured by various researchers (Deletics and Orr, 2005;German and Sevensson, 2002;Lau and Stenstrom, 2005;Morquecho and Pitt, 2003;Roger et al, 1998;Sansalone et al, 1998;Zanders, 2005). Table 3 shows particulate copper concentrations from these references.…”

“…For demonstration purposes, six distinct size groups were selected. Morquecho and Pitt's (2003) size ranges and copper concentrations were selected from Lau and Stenstrom's (2005) data. Linear interpolation between particle sizes in Lau and Stenstrom's data was used to match Morquecho and Pitt's particle size ranges.…”

The Importance of Particle Characterization in Stormwater Runoff

“…Many of the published studies of stormwater runoff report pollutant fractionation between dissolved (defined as filtered on a 0.45 \im filter) and particulate phases (e.g., Characklis and Wiesner, 1997;Helmreich et al, 2010;Sansalone et al, 1996), yet pollutants attach preferentially to certain size fractions as reported by other studies (e.g. Lau and Stenstrom, 2005;Morquecho and Pitt, 2003;Roger et al, 1998;Sansalone and Buchberger, 1997;Tuccillo, 2006). Thus, pollutant fractionation into particle size fractions is an important parameter to know when considering pollutant removal rates.…”