Letter: Clarifying phytoremediation data

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<ul><li><p>Clarifying phytoremediation dataReferences to research in OriSchippers article Phytoremediationreleases TCE to the atmosphere re-quire some clarification (1). Knowingthat phytoremediation uses complexliving organisms to deal with environ-mental problems, any one or combi-nation of factors at a site or in anexperimental arrangement may great-ly alter results.</p><p>In evaluating a remediation tech-nology, distinctive features of the pro-posed site or experimental designmust be considered. Determininghow unique factors may affect theobserved results should be the prima-ry goal rather than an attempt togeneralize the situation and the com-plications posed by these factors. Inbiological treatment, understandinghow organisms react to environmen-tal conditions, particularly thoseconditions unique to that site orexperimental design, is of prime im-portance. For living systems, thesereactions are not always predictable.Phytoremediation systems are ex-tremely complex, including plantmicrobe interactions and plants withdifferentiated tissues and vasculartransport systems. Media considera-tions add more complications asplants cross multiple media bound-aries, including groundwater (saturat-ed and unsaturated), soil, soil vapor,and open atmosphere. In consideringdifferent contaminants, one mediummay play a dominant role (e.g., soilfor PCBs and PAHs), or contaminantsmay readily exist and transfer be-tween media. In such cases, slightdifferences in conditions can leadto great differences in observations.</p><p>Newman et al. showed that plantsremoved the majority of the trichloro-</p><p>ethene (TCE) at a field site understudy; plant pathways examined in-cluded transpiration through theleaves, metabolism within the plant,degradation within the artificialaquifer (production of anaerobicbreakdown products), and mineral-ization within the plant system (2).Their studies of microbial activityshowed that TCE loss could not beaccounted for through that pathway.As in any field system, a total massbalance was not obtained; however,the researchers accounted for approx-imately 70% of the dosed TCE.</p><p>Ma and Burken recently publisheda paper that revealed another path-way for TCE in phytoremediation:diffusion from stems or trunks dur-ing transport (3). Plant stems containspecialized cells that aid gas ex-change with the atmosphere, so itwould seem apparent that TCE couldtransport through these cells as well.When applying phytoremediation toa field site, any one or combinationof these pathways may play a domi-nant role with different field sitesproducing different results. Thesetwo papers indicate there are variouspathways whereby TCE (and presum-ably other VOCs) can be removedfrom a contaminated aquifer; whatbecomes necessary is to determinewhat dominates removal for that site.For example, the microbial actionthat was minimal in the 1999 studymay prove to have a much largerrole at some sites, as was seen in aphytoremediation plot at CarswellAirbase (4). To better elucidate plantinteractions with groundwater contam-inants such as TCE, we are planninga joint study over the next year to si-multaneously look at the mecha-nisms described in both previousstudies. </p><p>References(1) Schipper, O. Environ. Sci. Technol. 2003,</p><p>11, 206 A.(2) Newman, L. A; et al. Environ. Sci. Technol.</p><p>1999, 33, 22572265.(3) Ma, X.; Burken, J. G. Environ. Sci. Technol.</p><p>2003, 37, 25342539.(4) Godsy, E. M.; Warren, E.; Pagnelli, E. E.</p><p>Int. J. Phyto. 2003, 5, 7387. </p><p>MILTON GORDONProfessor</p><p>University of WashingtonDepartment of Biochemistry</p><p>Seattle, Wash. </p><p>JOEL BURKENAssociate professor</p><p>University of Missouri, RollaDepartment of Civil, Architectural</p><p>and Environmental EngineeringRolla, Mont.</p><p>LEE NEWMANAssistant professor</p><p>University of South CarolinaArnold School of Public Health</p><p>Columbia, S.C.</p><p>Letter</p><p>310 A ENVIRONMENTAL SCIENCE &amp; TECHNOLOGY / SEPTEMBER 1, 2003 2003 American Chemical Society</p><p>ES&amp;T welcomes commentson relevant topics and articlesfound in the A-pages. A letterto the editor can be sent toManaging Editor, EnvironmentalScience &amp; Technology, AmericanChemical Society, 1155 16th St.,N.W., Washington, DC 20036; orby e-mail to est@acs.org. Pleaseinclude your e-mail or phonenumber. We reserve the right toedit the letter for content andlength.</p></li></ul>