Particulate- and dissolved-phase polychlorinated biphenyls and heavy metals interactions through a bioretention cell.

Abstract:

Many toxic contaminants of concern (COCs) are associated with urban stormwater, including persistent organic pollutants (POPs) and heavy metals. Many of these COCs bind to particulate matter (PM) washed off with stormwater in urban areas; these include polychlorinated biphenyls (PCBs), and heavy metals (e.g. copper and zinc). This work addresses both PM-bound and dissolved phase COCs, specifically PCBs, Cu, and Zn. The particle size distribution (PSD) of stormwater sediments has been shown to influence contaminant concentrations in stormwater runoff. PCBs are affiliated with the organic component of sediments and heavy metals affiliated with the mineral component, understanding partitioning of COCs and the influence of particle size distribution (PSD) is critical in reducing pollutant loads and through effective BMP design. The PSD can vary significantly, the d₅₀ between the first two storms in this study increased by a factor of 6.5. A bioretention cell should readily filter out PM-bound COCs, leaving behind dissolved phase constituents, first storm event 93% removal of TSS was observed. Dissolved COCs are then either adsorbed or pass through the media depending on the bioretention media’s adsorption characteristics and efficacy, as well as specificity to targeted COCs. In the influent samples, total PCB concentrations ranged from 164 ± 8.2 to 755 ± 22.7 ng/L and the concentration decreased by 89–92% after bioretention treatment. Dissolved Cu was also reduced through the bioretention cell from 9.5 ± 0.7 µg/L in the influent to 5.5 ± 1.5 µg/L, indicating 84% removal. It was hypothesized that the majority of PCBs will be filtered out through the bioretention cell since >90% of PCBs are associated with PM. However, heavy metals partitioning varies largely depending on several factors and can have >50% in the dissolved phase. This field study will measure dissolved and PM-bound PCBs, Cu and Zn through a bioretention facility. This work will also observe trends with COC and particle size associations.