Bioretention cells are known to effectively remove contaminants such as suspended solids, dissolved nutrients and trace metals, though with variable efficiencies. Limited research has investigated the fate of trace organic contaminants in bioretention cells, especially under field conditions. To fill this knowledge gap, we performed a tracer experiment at a bioretention cell site to obtain <i>in situ</i> field data at a high time-resolution with the goal of investigating the underlying transport, transfer and transformation mechanisms of various stormwater trace organic contaminants. A tracer mixture containing bromide, rhodamine WT, nitrate, phosphate, benzotriazole, and four organophosphate esters (OPEs) was injected as a pulse at the inlet of a bioretention cell located north of Toronto. Outflow samples were collected at different time points and analyzed to generate tracer breakthrough curves for these compounds. The results showed that the bioretention cell had a short retention time of less than 2 hours. The calculated effective volume ratio was 0.39 suggesting the presence of dead volume and/or preferential flow paths. The recovery rate was 95% for the water tracer bromide, and 35 and 51% for nitrate and phosphate, respectively, indicating removal of these nutrient species. Recovery of benzotriazole was 71%, consistent with this compound sorbing poorly to soil. Samples were analyzed by high-resolution liquid chromatography mass spectrometry – Orbitrap. Benzotriazole transformation products that were signatures of biotransformation and phytotransformation were found, suggesting potential for transformation between events. This field tracer experiment produced valuable information on the performance of the bioretention cell in mitigating trace organic chemicals. These results demonstrated the need to use new design strategies to effectively sorb or transform these contaminants, such as increasing the retention time, incorporating soil amendments, and selecting specific plant species for better treatment performance.<br/>

Multi-tracer experiment in a bioretention cell to study the transport of trace organic stormwater contaminants

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.