wastewater. Accuracy and precision were improved by 2 to 3 orders of magnitude over existing methods. The method uses precolumn orthophthaldialdehyde derivitization, reversed-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
Moolenaar found. EPA assumes that no threshold exists for carcinogenic ity and that risk assessment's goal is to estimate the upper limit of risk. The EPA's conservative approach contrasts those of England, Den mark, and the Netherlands, which recognize dose-response thresholds and actually estimate the incidence of human disease. Moolenaar pro poses a combination of both ap proaches, 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)
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, trichloroethylene, tetrachloroethylene, and 1,1,1trichloroethane and their binary and ternary mixtures. The mixtures showed nearly ideal behavior, con trary to group contribution ap proach predictions. Assuming ideal behavior simplifies application of groundwater transport models simu lating dissolution of chlorinated sol vent mixtures. (Environ. Toxicol. Chem. 1995, 24(1), 9-15)
REMEDIATION Explosives treatment Composting has been considered for the treatment of hazardous explo sives. W. H. Griest and colleagues studied the effectiveness of windrow composting of explosives-contami nated 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 effi cient than static pile or mechanically stirred composting. (Environ. Toxicol. Chem. 1995, 24(1), 51-59)
RISK Cultural differences Default assumptions in risk assess ments are treated much differently in America than in Europe, R. J.
ments because they include parame ters based on real-life phenomena such as cell division rate. Unlike sta tistical models, such as the linear ized multistage model, which are based on extrapolation, mechanistic models are more realistic and hold greater potential because of the reallife parameters, Crump says. How ever, he points out, most parameters still are estimated, making mecha nistic models just as theoretical as statistical models. He concludes this is clear evidence of the need for ex periments to identify and measure different dose-response parameters. (Risk Anal. 1994, 26(6), 1033-38)
Global warming beliefs Often people's knowledge concern ing global warming and its relation to high-level ozone depletion is con fused and incorrect, A. Bostrom and others found in a recent study. Most respondents to interviews and sur veys 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 au thors conclude that effective debate on climate change cannot occur un til the public becomes better in formed. (Risk Anal. 1994, 14(6), 95970, 971-82)
Mechanistic modeling K. S. Crump discusses using mecha nistic models for cancer risk assess
SOIL 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 deter mine trends and sources. Three dis tinct concentration patterns emerged from the archived sludges. These were related to atmosphericcombustion sources and two pentachlorophenol sources, with total toxic equivalence showing a maxi mum concentration during the mid1950s. The concentration of the con temporary samples was used to
Removing heavy metals with phytoextraction Can plant roots remove heavy metals from stream water? V. Dushenkov and col leagues 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 de creased overtime. Indian mustard roots concentrated the heavy metals by fac tors 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 phytoex traction 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 effi cient. 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
