wastewater. Accuracy and precision were improved by 2 to 3 orders of magnitude over existing methods. The method uses precolumn ortho-phthaldialdehyde derivitization, re-versed-phase HPLC separation, and fluorometric detection. Detection limits for amino acid were 10 to 100 nM, compared to about 2.5 μΜ for traditional methods. (Water Environ. Res. 1995, 67(1), 118-25)

MODELING Solvents in groundwater The concentration of chlorinated solvents in groundwater is based upon their aqueous solubility, about which data are limited. K. Broholm and S. Feenstra determined the aqueous solubility of chloroform, carbon tetrachloride, trichloroethyl-ene, tetrachloroethylene, and 1,1,1-trichloroethane and their binary and ternary mixtures. The mixtures showed nearly ideal behavior, con­trary to group contribution ap­proach predictions. Assuming ideal behavior simplifies application of groundwater transport models simu­lating dissolution of chlorinated sol­vent mixtures. (Environ. Toxicol. Chem. 1995, 24(1), 9-15)

REMEDIATION Explosives treatment Composting has been considered for the treatment of hazardous explo­sives. W. H. Griest and colleagues studied the effectiveness of windrow composting of explosives-contami­nated sediment. Explosives such as TNT, RDX, and HMX in compost and leachate were reduced by more than 97% in days. Mutagenicity similarly was reduced, and toxicity of leachates was reduced at least 87%. Windrow composting was more effi­cient than static pile or mechanically stirred composting. (Environ. Toxicol. Chem. 1995, 24(1), 51-59)

RISK

Cultural differences Default assumptions in risk assess­ments are treated much differently in America than in Europe, R. J.

Moolenaar found. EPA assumes that no threshold exists for carcinogenic­ity and that risk assessment's goal is to estimate the upper limit of risk. The EPA's conservative approach contrasts those of England, Den­mark, and the Netherlands, which recognize dose-response thresholds and actually estimate the incidence of human disease. Moolenaar pro­poses a combination of both ap­proaches, which would result in risk assessments with an upper bound of risk and an indication of the actual incidence of disease. (Regul. Toxicol. Pharmacol. 1994, 20(3), S135-41)

Global warming beliefs Often people's knowledge concern­ing global warming and its relation to high-level ozone depletion is con­fused and incorrect, A. Bostrom and others found in a recent study. Most respondents to interviews and sur­veys believed that global warming has already occurred because they confused the greenhouse effect with stratospheric ozone depletion. Few respondents identified fossil fuel combustion as the most important source of carbon dioxide. The au­thors conclude that effective debate on climate change cannot occur un­til the public becomes better in­formed. (Risk Anal. 1994, 14(6), 959-70, 971-82)

Mechanistic modeling K. S. Crump discusses using mecha­nistic models for cancer risk assess­

ments because they include parame­ters based on real-life phenomena such as cell division rate. Unlike sta­tistical models, such as the linear­ized multistage model, which are based on extrapolation, mechanistic models are more realistic and hold greater potential because of the real-life parameters, Crump says. How­ever, he points out, most parameters still are estimated, making mecha­nistic models just as theoretical as statistical models. He concludes this is clear evidence of the need for ex­periments to identify and measure different dose-response parameters. (Risk Anal. 1994, 26(6), 1033-38)

S O I L

Sludge application Concerns often are raised about the application to agricultural soils of digested sewage sludges containing chlorinated compounds. A. Sewart and colleagues studied a series of modern and archived sludges for these compounds in order to deter­mine trends and sources. Three dis­tinct concentration patterns emerged from the archived sludges. These were related to atmospheric-combustion sources and two penta-chlorophenol sources, with total toxic equivalence showing a maxi­mum concentration during the mid-1950s. The concentration of the con­temporary samples was used to

Removing heavy metals with phytoextraction Can plant roots remove heavy metals from stream water? V. Dushenkov and col­leagues evaluated a variety of terrestrial plants' roots in filtering heavy metals in a controlled series of laboratory experiments. The plant roots were exposed to aqueous solutions containing Zn, Cd, Cr, Ni, Cu, and Pb for up to 100 h, focusing on Pb because of its global concerns. All aqueous metal concentrations de­creased overtime. Indian mustard roots concentrated the heavy metals by fac­tors of 130 to 565-fold (dry weight basis). Tissue absorption and root-controlled precipitation of inorganic Pb compounds accounted for Pb removal. However, as aqueous Pb concentrations increased, the precipitation mechanism became more active in Pb removal. The authors suggest rhizofiltration has applications for Pb abatement in a variety of industries.

In a companion study, (P.B.A.N. Kumar et al.) the researchers studied phytoex­traction using a metal-accumulating plant, Indian mustard, grown on heavy metal spiked soils for up to 17 days. Results indicated that Indian mustard roots and shoots bioconcentrate Pb and other heavy metals; other plants were not as effi­cient. Factors influencing metal uptake include time of exposure, plant species, and Pb concentration. The authors conclude that phytoextraction can be a "green" alternative to heavy metal soil remediation, though more detailed study is needed to better understand the controlling mechanisms. (Environ. Sci. & Tech noi, this issue, 1232,1239)

VOL. 29, NO. 5, 1995 /ENVIRONMENTAL SCIENCE & TECHNOLOGY • 2 0 1 A

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examine potential agricultural up­take into the food chain. (Chemo-sphere 1995, 30(1), 51-67)

Immobilizing lead Lead in soil may be immobilized us­ing naturally-occurring materials such as phosphate rocks. Q-Y. Ma, T. J. Logan, and S. J. Traina devised a series of experiments in which finely ground phosphate rocks extract Pb. The results demonstrate that 39-100% of the Pb present in soil could be immobilized via phosphate rock-soil interactions. The authors con­clude that the quantity of phosphate rock used had a greater impact on Pb removal than did longer reaction time. Pb immobilization involved dissolution of phosphate rocks and precipitation of a fluoropyromor-phite-like mineral. This result is sup­ported by both XRD and SEM analy­sis. [Environ. Sci. TechnoL, 1995, 29(4), 1118-26)

WASTEWATER Extracellular enzymes Poor membrane permeability and the effects of contaminant concen­tration and nutrient limits often im­pede halogenated organic com­pound degradation in wastewater microbial populations. To overcome these problems, T. A. Lewis and col­leagues used extracellular catalysts immobilized in a flow-through reac­tor. They identified immobilized por­phyrins that would reductively deha-logenate carbon tetrachloride. The porphyrins were metallated with co­balt or nickel and included different substituents on the ρ position. The authors identified a cobalt porphyrin with aminophenyl substitution that can be immobilized on an electrode surface, allowing the central metal to be reduced without adding a chemi­cal reductant. (J- Environ. Qual. 1995, 24, 56-61)

Contributors to Research Watch are Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, CT; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, PA; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, OH; Richard Hurst, CHEMPET Research Corp., Moorpark, CA; Louis Kovach, Ecolife Associates, Wilmington, DE; and Margaret Whittaker, NSF International, Ann Arbor, MI.

2 0 2 A • VOL. 29, NO. 5, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY