Using Plants to Clean up Toxic Sites

In Urban Omnibus, urban designer Kaja Kuhl writes that in New York City “underutilized or vacant space can be a source of creative inspiration for urban agriculture, public parks, housing, community space, and the occasional mini-golf course.” However, before these abandoned lots can be reused, a thorough environmental assessment must be conducted and contaminated soils must be cleaned-up. Phytoremediation, a form of bioremediation that uses plants to clean up leach toxic chemicals from soils, may be the small-scale, cost-effective solution landowners need to make abandoned sites productive again. Kuhl contends phytoremediation is fully 90 percent cheaper than conventional remediation processes.

Through PlaNYC, New York City’s comprehensive climate change plan, Mayor Bloomberg has made a strong committment to the productive reuse of the city’s brownfields. In addition, the mayor recently signed the New York City Brownfield and Community Revitalization Act. PlaNYC, along with this new legislation, led to the creation of the Office of Environmental Remediation, which “oversees the environmental review of brownfield sites and offers assistance to property owners on the path to a Green Property Certification and potential redevelopment.” 

Even with the new policy and regulatory incentives, however, a huge share of abandoned lots are left vacant because of the high-cost of conventional remediation, which typically involves bringing in bulldozers to excavate contaminated soils. Kuhl argues city landowners need a cheaper way to remediate sites, and phytoremediation may provide that low-cost option. “Instead of removing tons of toxic soil and filling the site with new clean soil, plants remove contaminants from the soil and store it within their plant tissue. In some cases, the plants themselves then have to be removed as hazardous waste, other plants break down the toxins and eliminate them altogether.”

Phytoremediation works, but the correct plants must be used. “Contaminants successfully removed in field studies have included heavy metals, radionuclides, chlorinated solvents, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), pesticides and explosives. In order to successfully remediate toxins in soil or water, the appropriate plant groups have to be planted and monitored. Different plants have different remediative qualities.”Also, plants provide added value: “Improved air quality and reduction of storm water run-off are among the additional benefits of planting on sites that would otherwise be underutilized until funding for soil removal becomes available.”

Kuhl dug through NYC data and found that more than 11 percent of the city is an abandoned lot. If glued together, these disparate, small-scale lots would be the size of Manhattan. Also, most of the sites are small: 50 percent of all vacant lots of less than 2,500 square feet and 80 percent are less than 5,000 square feet. If applied across these small sites, low-cost and highly-effective phytoremediation techniques could have a powerful impact and help ensure future urban development is really just redevelopment.

Kuhl outlines eight steps for cleaning up an urban brownfield. To learn more, also check out an animation created using Google Sketchup that illustrates how plants and microbes clean up toxic sites.

In addition, the University of Arkansas Community Design Center has just released “Low Impact Development: a Design Manual for Urban Areas,” a 230-page guide that covers buildings, properties, streets, and open space, and includes detailed diagrams of a range of green infrastructure solutions. The guide is designed for “those involved in the development of urban property, from homeowners, to institutions, developers, designers, cities, and regional authorities.” The design center says “the goal is to promote implementation of LID technologies in urban areas through adoption of best practices in planning and design. An accompanying goal is to encourage reform in municipal codes which outlaw LID as a non-conforming stormwater management system in favor of conventional pipe-and-pond systems.”

Image credit: Urban Omnibus