Research Watch: Modes of action - Environmental Science

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Treatment Humic acid desorption Less is known about humic acid (HA) desorption from solid surfaces compared to their adsorption, although both processes are important for understanding mechanisms governing the interaction between HA and oxides. M. J. Avena and L K. Koopal investigated HA desorption from an iron oxide surface. Results indicate that HA adsorbed on an oxide at a relatively low pH that can be partially desorbed or mobilized by an increase in pH; at a constant pH, a change in supporting electrolyte concentration also led to some desorption. The magnitude of the observed effects depended on how the change in electrolyte concentration changes the interaction in the adsorbed layer. Desorption upon dilution at constant pH was very slow compared to the fast and reversible desorption upon a pH change. (Environ. Sci. Techno!., this issue pp. 2572-2577)

noted and analyzed. (Burkhard, L. P. "Comparison of Two Models for Predicting Bioaccumulation of Hydrophobic Organic Chemicals in a Great Lakes Food Web," Environ. Toxicol. Chem. 1998, 1 7(3), 383-393) Understanding stress in trees. A conceptual model of tree reactions and adaptation to multiple stress factors is presented. (Godbold, D. L. "Stress Concepts and Forest Trees," Chemosphrre 1998, 36(4/5), 859864)

Remediation Munitions sorption and fate. Most cyclonite (RDX) sorbed on soils is available for transport, indicating a need to remediate RDX-contaminated soils to protect groundwater. (Singh, J.; et al. "Long-Term RDX Sorption and Fate in Soil," /. Environ. Qual. 1998, 27, 572-577) Phytoremediation of metals. Results indicate that duckweed is a good species for phytoremediation applications involving metal-contaminated soil cleanup. (Zayed, A.; Gowthaman, S.; Terry, N. "Phytoaccumulation of Trace Elements by Wetland Plants: I. Duckweed," /. Environ. Qual. 1998, 27, 715-721) Total organic carbon removal. A combined adsorption-ultrafiltration process allows utilities to meet total organic carbon removal goals when coagulation is not effective. (Chang, Y-J.; Choo, K-H.; Benjamin, M. M.; Reiber, S. "Combined Adsorption-UF Process Increases TOC Removal," /. Am. Water Works Assoc. 1998, 90(5), 90-102) Waste site integrity. Results indicate that mammals, invertebrates, and

plants pose a threat to barrier integrity and isolation of hazardous wastes. (Bowerman, A.; Redente, E. "Biointrusion of Protective Barriers at Hazardous Waste Sites," /. Environ. Qual. 1998, 27, 625-632)

Sediments Contaminant bioavailability. Results suggest that the extent of solubilization of sediment-bound contaminants during gut-passage in deposit feeders is a key factor in determining contaminant uptake and absorption efficiency. (Weston, D.; Mayer, L. "Comparison of In Vitro Digestive Fluid Extraction and Traditional In Vivo Approaches as Measures of Polycyclic Aromatic Hydrocarbon Bioavailability From Sediments," Environ. Toxicol. Chem. 1998, 17(5) 830-840) Toxicity tests. Guidelines for testing proposed relationships between sediment chemistry and toxicity that are based on bulk chemistry can provide useful triggers for further analysis, but should not be used alone as indicators of toxicity. (O'Connor, T. P.; Daskalakis, K. D.; Hyland, J. L.; Paul, I. E; Summers, J. K. "Comparisons of Sediment Toxicity With Predictions Based on Chemical Guidelines," Environ. Toxicol. Chem. 1998, i7(3), 468-471)

Toxicity Modes of action. Results of molecular similarity, neural network, and discriminant analysis methods can be used to identify the modes of action of toxic chemicals. (Basak, S.; et al. "A Comparative Study of Molecular Similarity, Statistical, and Neural Methods for Predicting Toxic Modes of Action," Environ. Toxicol. Chem. 1998, i7(6), 1056-1064)

Membrane filtration of water. Membrane filtration results indicate the recovery efficiency of Giardia cysts and Cryptosporidium oocysts from water. (Falk, C. C ; Karanis, P.; Schoenen, D.; Seitz, H. M. "BenchScale Experiments for the Evaluation of a Membrane Filtration Method for the Recovery Efficiency of Giardia and Cryptosporidium From Water," Water Res. 1998, 32(3), 565-568) Trichloroethylene removed from water. Palladium-on-carbon catalysts were used to effectively remove trichloroethylene from water by a process of catalyzed dehydrohalogenation. (Perrone, L.; Prati, L.; Rossi, M. "Removal of Chlorinated Organic Compounds From Water by Catalytic Dehydrohalogenation," Appl. Catal, B 1998, i5(3/4), 241-246)

Wastewater Biological phosphorus removal. Results indicate that various bacterial populations, temperature, and process stoichiometry can influence biological phosphorus removal. (Brdjanovic, D.; et al. "Influence of Temperature on Biological Phosphorus Removal: Process and Molecular Ecological Studies," Water Res. 1998, 32(4) 1035-1048) Nitrogen removal. Results suggest that a partial nitrification/complete denitrification process can be used for nitrogen removal depending on performance requirements. (Potter, T.; Tseng, C; Koopman, B. "Nitrogen Removal in a Partial Nitrification/ Complete Denitrification Process," Water Environ. Res. 1998, 70(3), 334342)

Contributors: Michael Brauer, University of British Columbia, Vancouver, Canada; Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, Conn.; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, Pa.; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, Ohio; Louis Kovach, Ecolife Associates, Wilmington, Del.; Geoffrey Nobes, McGill University, Montreal, Canada; and Raewyn Town, Queen's University of Belfast, Northern Ireland.

SEPT. 1, 1998 /ENVIRONMENTAL SCIENCE S TECHNOLOGY /NEWS * 4 2 5 A