A Novel Approach to Phytoremediation of Persistent Organic Pollutants

The chemical stability and slow natural attenuation of certain persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) makes remediation of these compounds a particularly intractable environmental challenge. The problems posed by such organic pollutants are reflected in their listing as Persistent Biological and Toxic Chemicals by the U.S. Environmental Protection Agency, and in numerous studies such as a 2001 National Research Council report recommending further research on PCB treatment technologies. Improved treatment of POP-contaminated soils and sediments could significantly reduce the risk of contamination to the food chain and lower the costs of storing, transporting, and tracking POP-contaminated materials that must be sent to landfills. The bioavailability of POPs can decrease with time, as the chemicals gradually sorb to soil fractions. Recent research indicates that this process is reversible, however, as low molecular weight organic acids (LMWOAs) exuded by plant roots can break POP-soil bonds. Consequently, sequestration of POPs may not survive exposure to the rhizosphere. Such results not only highlight the need to remove or degrade POPs in the environment rather than relying on natural attenuation, but also suggest a novel method for addressing this need. In this research project, Edenspace Systems Corporation seeks to develop an innovative LMWOA-based phytoremediation technology for the removal of POPs from soils and excavated sediments. In cooperation with the Connecticut Agricultural Experiment Station, recently identified plant species that naturally produce large amounts of LMWOA root exudates, thereby mobilizing chlorinated organic pesticide compounds for plant uptake, will be tested for DDT and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane removal in weathered soils. LMWOAs will be applied directly to such soils to measure enhanced contaminant uptake by naturally accumulating plants and by Indian mustard. Successful Phase I results will be followed in Phase II with: (1) testing plant uptake of other POPs (e.g., PCBs and dioxin); (2) determining optimal LMWOAs (e.g., malate, citrate) for various POPs; (3) developing additional plant selection, cultivation, and treatment techniques to increase performance; (4) assessing possible increases in the rate of POP degradation as a result of increased microbial activity around plant roots; (5) assessing cost-effectiveness and ecological risks; and (6) conducting a field demonstration at a POP-contaminated site. The overall result of this research is expected to be a demonstrated POP phytoremediation technique that uses commercially available plants and rapidly biodegradable LMWOAs to provide cost-effective cleanup of many POP-contaminated soils.