As research progresses on the best ways to handle the toxin 6PPD-quinone, which forms from rubber tire debris and flows into stormwater systems, researchers at the University of British Columbia (UBC) say that the creation of engineered green infrastructure such as rain gardens may be a solution.
The tire toxin and other chemical contaminants eventually wash into waterways and endanger aquatic wildlife, proving particularly deadly for coho salmon, rainbow trout and some other fish. Rain gardens — technically called bioretention cells — could provide up to 90% protection, as they are engineered to reduce flooding and soak up contaminants when road runoff such as 6PPD-quinone is directed onto them.
In the new bioretention cells study, UBC researchers developed a rain garden in Vancouver, pumping 14,000 litres of water spiked with 6PPD-quinone onto the garden for four hours. The team tested the water draining from beneath the garden at frequent intervals and found only about 2% to 5% of the chemical made it through, with about 75% captured by the soil and plants.
The cell’s system area is 22 m2, and the contributing drainage area is 694 m2, with a ponding depth of 15 cm. There is a layer of mulch on the surface, and the unlined bottom contains an underdrain wrapped in clear gravel and geotextile, the study says.
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UBC researchers Timothy Rodgers and Rachel Scholes said they extrapolated their results using a computer model and estimated that more than 90% of the chemical would be blocked from entering waterways during an average year.
“Anywhere where you know there’s salmon, you should be trying to direct that runoff as much as possible into systems like this,” Rodgers said in the study’s announcement from UBC.
The study notes that “gaps remain regarding the transformation rates of 6PPD-quinone in soil,” as well as the potential for transport “through interflow and shallow groundwater flow,” however, the researchers suggest that 6PPD-quinone “is not likely” to be remobilized from soil.
Researchers in the Pacific Northwest have been studying why, for decades, as many as 90% of salmon would die when migrating through urban streams in an attempt to spawn in the Seattle, Washington, area. The scientists spent long hours isolating and testing molecules from some 2,000 chemicals in the tire-wear particles to identify whether a certain contaminant or combination of contaminants was particularly harmful. They narrowed it down to one named 6PPD-quinone, which, during testing, killed salmon within five hours of exposure to concentrations as low as 0.8 micrograms per litre.
A team at the University of Saskatchewan has been working to develop a treatment system using agricultural residues for the removal of toxic 6PPD compounds from urban runoff in Saskatoon.