The EPA (Environmental Protection Agency) defines a brownfield site as, "A site, or portion thereof, that has actual or percieved contamination and an active potential for development or reuse."  These sites usually exist in an urban setting and have potential real estate value or are surrounded by high value properties.  There are presently more than 450,000 brownfield sites in the United States.  These sites are waiting to be returned to some productive use.  Many of these areas accross the country were once used for industrial and commercial purposes and have since been abandoned; some are contaminated.  Because lenders, investors, and developers may fear the liability issues of these sites, they are more attracted to developing sites in pristine areas.  This leads to the abandonment of industrial facilities that create safety and health risks for residents, and the numbers of brownfield sites continues to increase.
    The EPA recently established its Brownfields Technology Support Center to ensure that decision makers are fully aware of the technologies available for site assesment and cleanup of brownfield sites.  The EPA encourages the use of innovative, cost-effective technologies to characterize and clean up contaminated sites.
    Phytoremediation, or the cleanup of environmental contamination using plants, offers an effective solution for the remediation and reconstruction of these brownfield sites.  Some of the phytoremedial techniques that can be used in such a setting include phytoextraction, phytovolatilization, phytodegredation, hydraulic control, vegetative caps, and constructed wetlands.  Phytoremediation might also be considered in conjunction with natural attenuation at a brownfield site.
    Phytoremediating brownfield sites may offer some advantages that either chemical or mechanical treatments don't offer.  Some of these advantages are reduced costs, positive community acceptance, aesthetic improvements of the site, and the ease of adaptability to redevelopment plans.  Since many brownfield sites contain low concentrations of contaminants, and over large amounts of surface area, phytoremediation can be a good alternative to either mechanical or chemical treatments.  Brownfield sites often contain a "collection" of contaminants.  Plant species used in phytoremediation can potentially treat a wide variety of contaminants or families of contaminants (such as metals, organics, etc.).  Brownfield sites are also often located in an urban setting and phytoremediation offers a solution through which soil remains in place during treatment and is usable after treatment.
    Although phytoremediation may be a promising way to treat a brownfield site, there are a few limitations to using this method of remediation.  One of these is the time it can take for a phytoremidial system to become effective.  It often takes several growing seasons before a phytoremediation setup to become completely effective.  This may prohibit the use of phytoremediation of sites where the time period for cleanup is limited.  Another limiting factor is root depth.  If the contaminant is buried deep within the soil, the roots of the plant species will not be able to take up the contaminant.  If the plants can successfully uptake the pollutant, then a remediator must be aware of the dangers involved with the translocation of the contaminant into plant tissues.  If the brownfield site typically attracts wildlife, this may pose a threat when the animals feed on the phytoremediating plant species.  In techniques such as phytovolitilization, sometimes the toxin that is released into the air can be more dangerous than its original form, which can be a threat to both wildlife and humans.  One more limitation of phytoremediation is that it may not work on all types of contaminants, and in this case another method of cleanup would be required.
 
 

Aspects of Plant Life in the Phytoremediation of Brownfields
Landscape Architecture and Phytoremediation 
References