RESEARCH WATCH
BIODEGRADATION Soil transport On the basis of field studies in which pesticides infiltrate groundwater earlier than predicted, B. E. Pivetz and colleagues studied the effect of preferential flow paths in soil on the biodegradation of pesticides. They added p-nitrophenol to soil columns containing either an artificial macropore or a channel of coarser textured soil, then calculated biodegradation rates as a function of breakthrough times. Breakthrough occurred earlier in the macropore and channel areas of the columns, but biodegradation rates were enhanced in these areas. {Soil Sci. Soc. Am. J. 1996, 60, 381-88)
DRINKING WATER
Membrane efficiency Membrane technologies that remove significant amounts of natural organic matter (NOM) are being used more frequently in drinking water treatment processes, primarily because of more stringent water quality regulations limiting disinfection by-products (DBP). Elevated DBP in treated water is often caused by NOM in raw water reacting with chlorine. J. A. Nilson and F. A. DiGiano investigated the influence of NOM composition on the efficiency of a nanofiltration membrane system for treating raw water. Results demonstrated a nearly 80% decline in membrane flux because of NOM in the membrane system. Further investigation indicated that the hydrophobic NOM fraction was responsible for almost all of the flux decline. Results suggest that a pretreatment system, such as powdered activated carbon, may remove enough hydrophobic NOM to make nanofiltration more feasible and cost effective. (J. AWWA 1996, 88(5), 53-66)
Assessing the bioavailability of sedimentary contaminants Many aquatic contaminants are adsorbed onto sediments, leading to the assumption that this reduces dispersion and bioavailability. However, exposure may be enhanced by deposit-feeding organisms. L M. Mayer and co-workers measured the solubilization of sedimentary contaminants by digestive fluids from two marine invertebrates. Though the animals were from unpolluted sources, their fluids had high preexisting concentrations of copper, lead, arsenic, and cadmium. Nevertheless, the researchers observed increased solubilization of contaminants relative to seawater, which they ascribed to amino acids and surfactants in the fluids. As much as 10% of the total contaminant sediment loading was considered bioavailable to the deposit-feeders, with observed variations between species. Depositfeeder digestive systems are important in the environmental cycling of contaminants, and the authors propose that this approach be used in routine environmental impact assessments. [Environ. Sci. Techno!., this issue, 2641-45)
Nitrate, pesticide removal Membrane processes can be used to remove contaminants that are not effectively treated by conventional processes. V Urbain and colleagues evaluated a new membrane bioreactor process in a pilot-scale study to determine its effectiveness in denitrification, disinfection, and pesticide and natural organic matter (NOM) removal. Denitrification occurred in a completely mixed bioreactor that used ethanol as the carbon source, and powdered activated carbon was added to remove NOM and pesticides. They passed the effluent through an ultrafilter to remove suspended solids and particulates. Results indicated that the process was highly effective in removing nitrates, NOM, pesticides, and other compounds. This was the first successful demonstration of nitrate and pesticide removal by a membrane bioreactor. (/. AWWA 1996, 88(5), 75-86)
Ozone and coagulation The character and concentration of chemical compounds in raw water can affect particle destabilization and coagulation. Typically, oxidation is used to enhance coagulation in raw water. Few studies exist that evaluate ozone as an oxidant in the oxidation of extracellular organic matter (EOM) produced by algae. A.
3 2 4 A • VOL. 30, NO. 8, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Paralkar and J. K. Edzwald investigated the effects of ozone on EOM oxidation and the subsequent effects on coagulation. Results indicate that EOM impact on coagulation depends on the type of algae and the EOM concentration. At low doses, ozone caused the release of EOM from algae and enhanced coagulation. At higher ozone doses, EOM was oxidized more completely and had little effect on coagulation. (/. AWWA 1996, 88(4), 143-54)
MEASUREMENTS Colloid composition Because of their large surface-tomass ratio, colloids play an important role in contaminant transport and immobilization. However, methods to reliably characterize their composition are scarce. Y. E. Freedman and co-workers used solid sampling graphite furnace atomic absorption spectrometry to determine copper and cadmium content in groundwater colloids. They collected colloids from a groundwater aquifer by passive filtration onto a dialysis cell in the field. Results of subsequent analysis by solid sampling agreed with those obtained by total digestion. The copper and cadmium content of the colloids varied with depth below the water table and also
0013-936X/96/0930-324AS12.00/0 © 1996 American Chemical Society
Sediments used to monitor water quality M. B. Nilsson and colleagues proposed near-infrared reflectance (NIR) spectroscopy of lake sediments as a rapid, cost-effective method for environmental monitoring of water quality. They evaluated spectra of the top centimeter of sediments in Swedish lakes along with historical measurements of pH, total phosphorus, and total organic carbon. Using partial least-squares regression, the authors developed models predicting each water quality parameter from entire NIR spectra of the sediment. They achieved the best predictions using water quality measurements averaged over the preceding four years. The method could be used for longterm monitoring of lakes, because relatively few sediment samples would be required to establish timeintegrated averages of water quality. [Environ. Sci. Technol., this issue, 2586-90}
with time, reflecting the natural fluxes of colloids that have variable metal contents. By using this method, sample collection for field analysis took two days, whereas sample collection for analysis by conventional methods, which require larger samples, would require 31 days. (Environ. Sci. Technol. 1996, 30(7), 2270-77)
Determining DNA adducts An important step in carcinogenesis occurs when a chemical or its metabolite modifies DNA, forming a DNA adduct. However, determining these adducts is difficult because the chemical modifies only between one in 106 and one in 1012 bases, leading to very low concentrations. J. P. Barry and colleagues coupled capillary zone electrophoresis (CZE) to negative ion electrospray mass spectrometry (ES-MS). They were able to determine adducts formed between DNA and a benzo[a]pyrene metabolite. They introduced the adducts into the CZE apparatus with a sample stacking technique that allowed a 1000-fold preconcentration. To increase sensitivity and selectivity, the ES-MS was operated to selectively monitor reaction. With this technique they determined adducts as low as 85 pg. When they combined the technique with a solid-phase ex-
traction procedure, they determined concentration levels as low as 4 adducts per 107 unmodified bases. {Anal. Chem. 1996, 68(8), 1432-38)
Fewer cleanup procedures Extensive preconcentration and cleanup techniques, which generate large amounts of waste, are required to determine polycyclic aromatic hydrocarbons (PAH) or polychlorinated dibenzo-p-dioxins (PCDD) in serum. S. R. Sirimanne and colleagues found that micelle-mediated extraction can be used with HPLC to determine these compounds without extensive cleanup procedures. They added Triton-X (0.5-12%) and sodium chloride (2.5-5.5 M) to a 0.5or 5-mL aliquot of serum, which was mixed, heated, and centrifuged with the supernatant decanted. They then removed coextractives from the supernatant by precipitation with acetonitrile and filtration and subjected a 50-pL aliquot to HPLC analysis. Using this technique, they recovered 100% of PAH spiked at 250-550 ppb and 97% of PCDD spiked at 3.9-4.4 ppm. {Anal. Chem. 1996, 68(9), 1556-60)
SOIL Single-species tests J. E. Kammenga and colleagues developed a toxicity test to assess the effect of soil contaminants using a single species. The test was conducted with an artificial soil composed of 70% sand, 20% kaoline clay, 10% Sphagnum peat, and the nematode Plectus acuminatus. They added cadmium, copper, and pentachlorophenol to the soil, then counted juvenile and adult species of the nematode after three weeks of incubation, using the ratio of juvenile to adult nematodes as a test parameter. The authors concluded that single-species tests could supplement present toxicity tests that use other invertebrates in artificial soil. {Environ. Toxicol. Chem. 1996, 25(5), 722-27)
Sorption coefficients In order to conduct accurate fate and transport modeling, sorption of organic compounds to soils must be understood. Typically, sorption coefficients have been determined using batch, column, and centrifuge tech-
Photodegrading furans in lake waters The environmental fate of polychlorinated dibenzofurans in aquatic systems is important because these compounds are highly toxic. K. J. Friesen and colleagues studied the aquatic photodegradation of 2,3,7,8tetrachlorodibenzofuran and 2,3,4,7,8pentachlorodibenzofuran in a distilled water-acetonitrile solution and in lake water. Results showed that these two compounds had half-lives of 1.2 and 0.19 day, respectively, in lake water and half-lives of 6.3 and 46.2 days, respectively, in the distilled water-acetonitrile system. They attributed the enhanced degradation rates in the lake water to the presence of unknown photosensitizers. Results also showed that photodegradation occurred by way of reductive dechlorination, which produced several less chlorinated dibenzofurans. (Environ. Sci. Technol. this issue, 2504-10)
niques in soils with water contents above field capacity. E. A. Rochette and W. C. Koskinen determined the sorption coefficient of atrazine in soils with water contents below field capacity using supercritical fluid extraction with carbon dioxide (C02). The density of supercritical fluid C02, soil water content, and temperature each affected the sorption coefficient. Although the method is rapid, requiring less than two hours, and holds promise for removing organics from aqueous soil phases, the authors call for more studies to determine the method's sensitivity. {Soil Sci. Soc. Am. J. 1996, 60, 453-60)
Pesticide mobility Widespread pesticide use has led to concerns about pesticide transport through soils into groundwater. E. L. Kruger and colleagues studied the relative mobilities of atrazine, atrazine degradates, metolachlor, and simazine in a series of 10 soils using soil thin-layer chromatography (STLC). Radiolabeled pesticides were spotted on STLC plates prepared from the different soil types, and the plates were developed with ultrapure water, with the mobility imaged by X-ray film. The pesticides were split into four groups based on mobility. All compounds' mobilities correlated negatively with organic matter con-
VOL.30, NO. 8, 1996/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 3 2 5 A
