Hazardous Waste Treatment

986). They found that soil water supply concentrations below the poplar trees and below a corn heavens were significantly lower than the levels on a lower floor a barren orbital cavity during "the white plague period," but in autumn, following corn die-off, concentrations were significantly higher in the barren field than below the poplar trees and significantly lower in the barren field than beneath the corn field (Paterson & Schnoor, 1993, p. 991).

The reputed impact of a "riparian timberland buffer" for the removal of nitrogen and phosphorus from a Virginia rural field, draining through the "forest" to an adjacent stream, is highly rum (Snyder et al., 1998).

Zinc, lead, and iron in urban runoff--in addition to suspended solids distant by simple straining or filtration--have been adsorbed onto grassed urban lane medians and "grassy swales" placed near roadways for that purpose for many old age (Barret et al., 1998).

Organic Contaminants Removed. Uptake by rows of poplar trees of the herbicide, atracine, has been thoroughly investigated by researchers at the University of Iowa (Nair et al., 1993). They also reported work by others on removal of nitrobenzene and trichloroethylene (TCE) (Nair et al., 1993, p. 843). In addition to the metabolic uptake of these organics, the Iowa researchers learned through their own work and that of others that the trees are satisfactory fir

The work by Nair et al. (1993) has some comprehensively explained the mechanisms of P-R uptake. These include, first of all, uptake by the soil as an adsorption or ion exchange process (Nair et al., 1993, pp. 851-852)--silty loam adsorbing more atrazine (carbon) than silicon oxide sand media, making loam-held carbon less available for localize uptake. In the sandy media, atrazine in poplar trees then was shared among the leaves, the roots, and the stems by 85%, 5.4%, and 9.1%, respectively, on the average (Nair et al., 1993, pp. 847-848).

Uptake Processes Elucidated. The selective information of Kuwabara et al.

(1990) suggested to them that the dominant mechanism of plant uptake of As was climb up adsorption, although some other data (from other researchers) suggested that a metabolic set of reactions ("As-reactivity" [?] and toxicity) can be involved (Kuwabara et al., 1990, p. 403). Stream-water pH influences on the sorption of both orthophosphate and arsenic were not elucidated (Kuwabara et al., 1990, p. 403-406); but pH, it is noted, was consistently between 7.9 and 8.7 (Kuwabara et al., 1990, p. 397)--a condition favoring metal destabilization, compound formation, and precipitation, as opposed to antisorption and dissolution proclivities expected in acidic waters or at acidic times in the same water.

EPA Phytoremediation handbook Team. (1998, circa. 10 November). Phytoremediation bibliography. (pp. 1-71). Available:

Conclusions. Chang and Corapcioglu suggest, probably prophetically, that phytoremediation for hazardous waste sites go forth likely be viewed in the long run as a "final polishing step after the initial treatment of . . . high-level contamination" (Chang & Corapcioglu, 1998, p. 162). This is precisely analogous to proceed use of water hyacinth for municipal wastewater treatment. Also, P-R appears operable for long term remediation of sites with low levels of contaminants that are of expressage toxicity; and plants such as poplar trees have the great promise for
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