Urban runoff is a significant source of heavy metals that can harm rivers and ecosystems.
Metals such as cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) often wash into waterways during rainy weather or snowmelt in urban areas.
These metals are problematic because they can harm aquatic life and pose risks to human health. They persist in the environment, accumulate in living organisms, and exhibit toxicity.
Heavy metals enter urban runoff from a variety of sources, such as car emissions, construction sites, fertilizers, and even the atmosphere. They are typically found in dissolved form, making them more readily available for biological uptake.
Additionally, heavy metals tend to attach to fine particles in the water. The concentration of heavy metals in runoff is influenced by the type and intensity of rainfall.
Green infrastructure (GI) is an effective method for managing heavy metals in urban stormwater. Unlike traditional gray infrastructure, which includes gutters and pipes, GI utilizes natural elements such as soil, plants, and microbes to purify rainwater at its source.
One example of GI is a bioretention cell, commonly known as a rain garden. This is a shallow depression designed to reduce stormwater and enhance its quality by filtering runoff through soil and plant roots.
The City of Columbus, Ohio, has begun using Green Infrastructure (GI) to improve its water management, primarily to address sewer overflows.
In 2005, Columbus entered into agreements with the Ohio Environmental Protection Agency (EPA) to address sewer overflow issues. By 2009, the city proposed a Wet Weather Management Plan that included building underground tunnels and expanding wastewater treatment facilities.
However, in 2012, following guidance from the US EPA, the plan was changed to incorporate GI as part of the solution to these sewer overflow issues, specifically in areas of Columbus with separate sewer systems.
The Ohio EPA approved this change and selected the Clintonville neighborhood to pilot the initiative, called Blueprint Columbus.
The study published in the Journal of Hazardous Materials, “Retrofitted watershed scale green infrastructure reduces heavy metals in urban stormwater from residential land use” on 15 October 2025, examines how installing “green infrastructure” (GI) at the watershed scale can affect the amount of heavy metals in urban stormwater runoff from residential areas.
Green infrastructure in the study refers to bioretention cells (vegetated filtration areas), permeable pavement, and other “low-impact development / sustainable drainage” features designed to manage and treat stormwater naturally rather than relying solely on conventional (“gray”) drainage.
The project is part of Blueprint Columbus, a 30-year community effort to install green infrastructure in local neighborhoods.
The study monitored three watersheds in the Clintonville neighborhood of Columbus, Ohio: Beechwold, Cooke-Glenmont, and Indian Springs. It focused on stormwater hydrology and water quality at the storm sewer outfalls of each watershed. Beechwold served as the control watershed, while Cooke-Glenmont and Indian Springs were designated as the treatment watersheds.
A 3.5-year study compared watersheds before and after the installation of green infrastructure (GI) to see its effects on heavy metal levels.
The results showed that the Cooke-Glenmont treatment watersheds with GI experienced significant reductions in heavy metals, including copper (Cu), nickel (Ni), and zinc (Zn), attributable to the presence of two large bioretention cells and a smaller one.
Before GI installation, heavy metal levels increased with heavy rainfall, but after GI installation, GI reduced this impact by capturing and treating runoff through methods such as filtration and biological uptake.
In contrast, the Indian Springs treatment watershed, with 32 smaller offline bioretention cells and 4 permeable-pavement roads, showed no reduction in heavy metal concentrations. The study suggested that this lack of improvement was due to design and implementation issues.
The study recommends implementing online bioretention cells in series, optimizing their design, and ensuring proper maintenance to enhance efficiency. It emphasizes the importance of engaging with local communities early in the process as a key strategy for gaining public support for green infrastructure (GI) installations.
Overall, the study concludes that a well-designed and well-maintained GI system in residential areas can effectively reduce heavy metal levels in nearby waterways.
In short, implementing more of these systems in urban areas could make the city’s ecosystems healthier and more resilient, according to the study’s lead author, Joseph Smith. “Not only does green infrastructure improve water quality, but it also helps cities to be cooler because it adds more green space. The goal is to design spaces where people want to walk around and enjoy beautiful surroundings and experience the many ecosystem services created,” Smith says.
From an asset management practice perspective, it is essential that GI bioretention cells remain accessible and maintainable in the long term.
The lack of access and the inability to maintain the system create another set of issues in providing the long-term service these assets require.
Sources
Smith, J. S., Bernard, K., Boening-Ulman, K. M., Martin, J. F., Tirpak, R. A., Wituszynski, D. M., & Winston, R. J. (2025). Retrofitted watershed scale green infrastructure reduces heavy metals in urban stormwater from residential land use. Journal of Hazardous Materials, 498, 139808. https://doi.org/10.1016/j.jhazmat.2025.139808
Woodall, T. (2025, October 15). How green infrastructure is revamping city storm sewers. Ohio State News. Retrieved from https://news.osu.edu/how-green-infrastructure-is-revamping-city-storm-sewers/
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