PHYTOREMEDIATION TECHNOLOGY

Introduction. Phytoremediation is "the use of plants to remove, contain or render harmless environmental contaminants in water, soil and sediments" (BIOMINET, 1998a, p. 2). It is fairly new as an attempt to treat hazardous waste sites, although it has been used for decades for wastewater polishing or the straining of pollutants from urban runoff through grass buffer areas.

Inorganic Contaminants Removed. Kuwabara et al. (1990) studied the uptake of arsenic from mine tailings by algae and attached aquatic plants ("submerged macrophytes") in a 57-km stretch of a South Dakota stream (Kuwabara et al., 1990, p. 395). The uptake of arsenic was affected by an apparent preferential uptake of phosphorus, if present in the water, principally in the orthophosphate form (Kuwabara et al., 1990, p. 403).

Cadmium in an embayment of the Hudson River estuary, resulting from 1953-71 discharges of wastes from a nickel-cadmium battery plant, was identified by Thomann et al. (1993) to be influenced by several biological forms (blue crab and benthic worms), but aquatic plant species were not identified as being significant influencers of cadmium in either the sediments or the overlying water column (Thomann et al., 1993, p. 424).

Driven by a concern that 18% of Iowa's rural wells show nitrate-N concentrations exceeding Federal standards (10 mg/L NO3-N), Paterson and Schnoor (1993) studied the uptake of nitrate by plant

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) 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. Hard by the Hudson estuary, Cd sorbed into the flesh of the blue crab--a much-harvested local delectable--was "about 25 times" the acceptable level over the 1970's and 80's (Thomann et al., 1993, p. 437). Uptake and accumulation by the crab was specifically noted in the "hepatopancreas [an edible organ]" (Thomann et al., 1993, p. 436). But plant uptake or sorption were mechanisms utterly ignored--among those postulated and demonstrated: sorption/desorption between dissolved and particulate cadmium forms, diffusive exchange with bed sediments, exchange of particulate cadmium due to benthic (-worm) stirring ("bioturbation"), net deposition (settling), and advective transport (Thomann et al., 1993, p. 426). The work by Nair et al. (1993) has most comprehensiv
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