Stormwater Bioretention Cells Are Not an Effective Treatment for Persistent and Mobile Organic Compounds (PMOCs)

Abstract

Bioretention cells are a stormwater management technology intended to reduce the quantity of water entering receiving bodies. They are also used to reduce contaminant releases, but their performance is unclear for hydrophilic persistent and mobile organic compounds (PMOCs). We developed a novel eight-compartment one-dimensional (1D) multimedia model of a bioretention cell (“Bioretention Blues”) and applied it to a spike and recovery experiment conducted on a system near Toronto, Canada, involving PMOC benzotriazole and four organophosphate esters (OPEs). Compounds with (log D OC) (organic carbon-water distribution coefficients) < ∼2.7 advected through the system, resulting in infiltration or underdrain flow. Compounds with log D OC > 3.8 were mostly sorbed to the soil, where subsequent fate depended on transformation. For compounds with 2.7 ≤ log D OC ≤ 3.8, sorption was sensitive to event size and compound-specific diffusion parameters, with more sorption expected for smaller rain events and for compounds with larger diffusion coefficients. Volatilization losses were minimal for all compounds tested. Direct uptake by vegetation also played a negligible role regardless of the compounds’ physicochemical properties. Nonetheless, model simulations showed that vegetation could play a role by increasing transpiration, thereby increasing sorption to the bioretention soil and reducing PMOC release. Model results suggest design modifications to bioretention cells.

Bioretention Cells Provide a 10-Fold Reduction in 6PPD-Quinone Mass Loadings to Receiving Waters: Evidence from a Field Experiment and Modeling

“…Herein, we conducted a 6PPD-quinone spike and recovery test on a full-scale bioretention cell in Vancouver, Canada. We interpreted and extended our analysis using the Bioretention Blues model of organic contaminant fate in bioretention systems . The goals of our study were to (A) Experimentally assess the effectiveness of mature bioretention systems for reducing the discharge of 6PPD-quinone, (B) model the performance of bioretention systems for removing 6PPD-quinone under different hydrological conditions, and (C) model dominant processes in 6PPD-quinone fate in bioretention systems and determine gaps in our understanding of those processes.…”

Emissions and fate of organophosphate esters in outdoor urban environments

“…Depending on the local context, this green infrastructure could range from engineered systems like bioretention cells to a simpler redirection of stormwater from rooves to, for example, gardens or other vegetated areas. Encouragingly, sorption-based green infrastructure technologies are effective for compounds with log K OW > ~3.8 46 , meaning that for many of the more hydrophobic chemicals mobilized by cities (that would not be released to water in non-urban environments), green infrastructure should be an effective way to decrease loadings to aquatic ecosystems. One additional note of optimism is that our results suggest that increasing the amount of green space in a city can increase a city’s urban metabolism, directly removing chemical contaminants from the air and prevent them from being washed into the water, at least for those compounds that phytotransform into less toxic products.…”

“…For instance, as most food production occurs outside of cities, processes which act to retain OPEs in urban areas are likely to reduce human exposure via diet. However, if these processes simply mobilize OPEs to surface water, they will increase human exposure through drinking water, especially for the chlorinated OPEs, which are poorly removed by water treatment systems 46 , 48 , 49 and therefore may accumulate in water cycles 5 . Aquatic ecosystems are believed to be sensitive to certain OPEs 50 , so moving OPEs from the atmosphere to water would also increase environmental damage.…”

Where do they come from, where do they go? Emissions and fate of OPEs in global megacities

“…Depending on the local context, this "green infrastructure" could range from engineered systems like bioretention cells to simpler redirection of stormwater from rooves to, for example, gardens or other vegetated areas. Encouragingly, sorption-based green infrastructure technologies are effective for compounds with log K OW > ~ 3.8, 47 meaning that for many of the more hydrophobic chemicals mobilized by cities (that would not be released to water in nonurban environments), green infrastructure should be an effective way to decrease loadings to aquatic ecosystems. One additional note of optimism is that our results suggest that increasing the amount of green space in a city can increase a city's "urban metabolism", directly removing chemical contaminants from the air and prevent them from being washed into water, at least for those compounds that phytotransform into less toxic products.…”

“…For instance, as most food production occurs outside of cities, processes which act to retain OPEs in urban areas are likely to reduce human exposure via diet. However, if these processes simply mobilize OPEs to surface water, they will increase human exposure through drinking water, especially for the chlorinated OPEs, which are poorly removed by water treatment systems 47,49,50 and therefore may accumulate in water cycles. 5 Aquatic ecosystems are believed to be sensitive to certain OPEs, 51 so moving OPEs from the atmosphere to water would also increase environmental damages.…”