Pollutant transport by colloids In soils and groundwater aquifers, colloids act as contaminant carriers and facilitate pollutant transport. R. Kretzschmar and H. Sticher used soil columns and a short-pulse chromatographic technique to investigate the influence of colloidally adsorbed humic acid, solution Ca2+ concentration, and trace amounts of adsorbed Cu2+ and Pb2+ contaminants on the transport and deposition kinetics of colloidal hematite particles. They found that natural organic matter, such as humic acids greatly increases colloid mobility. Results demonstrate that colloidally adsorbed trace metal contaminants can be transported into uncontaminated zones when solution chemistry is dominated by Ca2+ and that colloid mobility and stability are sensitive to Ca 2+ rnncentration Effects of t r a r p metal contaminants nn coMniri mnhility w/pre small compared \A/ith the [Environ
Efficient herbicide analysis More efficient methods are needed for analysis of monomethyl tetrachloroterephthalate and tetrachloroterephthalic acid in groundwater aquifers. These compounds are metabolites of dimethyl tetrachloroterephthalate, a widely used herbicide. R. A. Carpenter and colleagues report that with ion pair chromatography and direct injection of unprocessed well water samples, they could unambiguously analyze for these metabolites in 25 minutes. Comparison of their analysis technique widi EPA Method 515.1 indicated enod agrppment The latter method is lab-intensive and not tractable for screening large ni i m—
bers of samples The procedure enables on-column injection of large sample volumes provides sensitivity needed for potable water assays and can be used in unattended overnight analyses of samples at significantly lower cost (Anal Chem 1997 69(16) 3314-20)
Ca 2+ concentratinn pffpct QM Tprhnnl ,hic iccno
PESTICIDES containing selected chemical contaminants. (Epidemiology 1997, 8(4), 347-54)
MEASUREMENTS Aldehyde analysis Hydrazine reagents are used for determination of aldehydes and ketones in liquid and air samples. However, they also react with ozone and nitrogen dioxide, and this confounds chromatographic analysis of the organic compounds. A. Biildt and U. Karst synthesized a new hydrazine derivatization agent, l-methyl-l-(2,4-dinitrophenyl)hydrazine, and used it to successfully analyze for the presence of carbonyl hydrazones, which formed from reaction of the reagent with carbonyl compounds found in car exhaust. The hydrazones are produced when the reagent reacts quantitatively with carbonyl compounds in the presence of an acid catalyst. Although this reagent also reacts with ozone and nitrogen dioxide, the reaction product, N-methyl-2,4-dintiroaniline, does not interfere with analysis of sample compounds. (Anal. Chem. 1997, 69(17), 3617-22)
Mobility of lindane The physical and chemical properties of lindane (y-hexachlorocyclohexane), an insecticide used worldwide in a variety of domestic and agricultural applications, suggest it should not readily leach from surface water into groundwater; however, this has not been demonstrated. D. B. Donald and co-workers compared lindane isomer concentrations found in prairie lakes and ponds, recharged by surface runoff from agricultural lands, with amounts found in prairie springs that originate from aquifers
charged from cultivated lands. They also examined concentrations of lindane in rivers whose flow originated either from large lakes or flood plain groundwater discharges. Results indicate that dominant isomeric forms of lindane have limited potential for transport through aquifers and that surface waters originating from groundwater sources usually do not contain detectable concentrations of lindane. (Environ. Toxicol. Chem. 1997 26(9) 1867-72)
RISK Sludge dioxin risks Use of dioxin-contaminated pulp and paper mill sludge poses risks that should be evaluated. O. Meyn and co-workers examined dietary exposure pathways in an evaluation of potential effects on terrestrial wildlife of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCCD) in land-applied pulp and paper mill sludges. The generic analysis, which evaluated uncertainties with Monte Carlo techniques, aimed to establish and implement 3. non.~site-specific risk evaluation methodology that later could be used to assess risks at specific current or future land-application sites. Results of the assessment indicate that the most at-risk species are shrews and other animals that consume large amounts of food in which TCCD is bioconcentrated or bioaccumulated. Correlation with field studies was generally good. The analysis was consistent with EPA guidance on uncertainty characterization and serves as a case study of application of EPA's ecological risk assessment methodology framework (Environ Toxicol Chem 1997 16(9) 1789-801)
Acidification recovery study Natural organic acids influence surface water acidity, but little is known about how their neutralization capacity affects the recovery of streams and lakes from acid deposition associated with industrial activities. J. Hruska and colleagues performed field experiments to evaluate the acidification and subsequent recovery of a bog stream that was subjected to chronically high acid deposition. Only 10% acid neutralization was observed when sulfuric acid or sodium bicarbonate was added separately to the water, despite the high concentration of organic acids in the stream. A Gaussian model of organic acid dissociation was used to interpret observations. The authors suggest that the limited buffering provided by natural organic matter is due to the heterogeneity of proton binding sites. This suggests that organic acids will not hinder the recovery of surface waters when acidification inputs from industrial activities decrease. (Environ. Sci. Techno!., ,his issue, pp. 3677-811
VOL.31, NO. 12, 1997/ENVIRONMENTAL SCIENCE & TECHNOLOGY/NEWS " 5 4 5 A
