wintering areas are near major agricultural sites, where pesticide applications are high. M. A. Mora tested this hypothesis by comparing POPs, such as DDE, found in resident and migrant birds in Mexico with pesticide residues found in resident birds in the southwestern United States. The data suggest that DDE is no more prevalent in birds in Mexico than those in the United States. Additional work is needed on birds in southern Mexico where DDT was heavily applied to cotton and is still used for malaria control (Environ Toxicol Chem 1997 i6(1) 3-11)
REMEDIATION Organo-clay sorption Organo-clays can be used to remediate nonpolar, nonionic, organic compounds such as benzene and toluene. Organo-clays are clays in which the interlayer cations have been replaced by large organic cations that can sorb organic contaminants. W. F. Jaynes and G. E Vance studied the sorption of a mixture of benzene, toluene, ethylbenzene, and xylenes (BTEX) to organo-clays constructed with different interlayer organic cations. Components of the BTEX mixture were sorbed more effectively than those from a pure phase of the compound The BTEX mixture increased the organic matter content within the organo-clay plex thereby enhancing partitioning into the organic matter [Soil Sci Soc Am J 1996 60 1742-49)
Binding heavy metals in soil n
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boil remediation methods tor heavy metals ideally should oe cheap and work without destroying soil structure or fertility. B. A. Lothenbach and colleagues report on the adsorption of heavy metals onto aluminum-based binding agents, Al-montmorillonite and AI13-montmorillonite. Under batch conditions, Ni, Cu, and Zn were specifically adsorbed on the agents. Optimum pH ranges for adsorption on Al-montmorillonite were pH 6-8 for Ni and Zn, pH 4-6 for Cu, and pH 7-9 for Cd. Al13 adsorbed Ni, Cu, and Zn, in the pH range 6.1-7.5 but formed soluble complexes at lower pH. No significant immobilization of Pb occurred. The agents should have little effect on soil nutrients such as Mg and K. {Environ. Sci. Technoi., ,his issue, pp. .452-62)
selecting cosolvents to enhance HOC solubility in environmental engineering projects. [Environ. Toxicol. Chem. 1996, 15, 2233-39)
RCRA compounds in sludge Activated sludge treatment systems have been designed to remove readily biodegradable compounds from domestic sewage. Little information is available on their ability to remove toxic compounds such as those regulated by the Resource Conservation and Recovery Act (RCRA). S. K. Bhattacharya and colleagues studied the efficiency of an activated sludge process in removing 11 RCRA compounds. A mixture of 0.25 mg/L of each compound was fed continuously to an acclimated activated sludge reactor. Reductions in the compounds caused by volatilization sorption and biodegradation were measured for seven weeks Volatilization losses in primary sedimentation exceeded 10% for carbon tetrachloride and related compounds Removal of >949' was onstrated for 9 of the 11 compounds [Water Environ Res 1996 68 260-69)
risk assessment process. It includes issues such as pathogen/host interactions, secondary spread, immunity, and propagation of the microorganism. The authors note the need for better methods to incorporate factors such as age and immune status. [Risk Anal. 1996, 26(6), 841-48)
Accepting QRA Despite heated criticism, quantitative risk assessment (QRA) remains the cornerstone of national environmental protection efforts in the United States. A. Tal argues that environmentalists forego chances to better protect public health by not accepting some form of QRA. Some perceive the focus on QRA, instead of pollution prevention, as an admission that pollution is tolerable. Despite imperfections, statutes and court decisions have established the permanence of QRA, says the author. [Environ. Forum 1997, 14(1), 13-21)
WASTEWATER
HOC solubility
Designing batch reactors
The solubility of a hydrophobic organic compound (HOC) determines how the compound will partition itself among air, water, and other environmental media. The presence of organic cosolvents can affect solubility and partitioning. A. Li and associates studied correlations between the change of naphthalene solubility and various physicochemical properties of cosolvents. They measured nine physicochemical parameters of 21 cosolvents witii correlations to the solubility of naphthalene in water. The solubility parameter which is a measure of the cohesive forces of the solvents had the strongest correlation It thus provides a convenient screening tool for
The sequencing batch reactor (SBR) is an increasingly popular biological system for treatment of industrial and municipal wastewater. G. F. Nakhla and colleagues report development of a model for designing SBRs for inhibitory and noninhibitory wastewater. They used die Monod equation to describe microbial growth kinetics. Their model predicts cell and substrate concentrations tiiroughout the treatment cycle and emphasizes the importance of feed rate as an operating parameter. Model predictions were compared with actual data derived from the literature for SBRs Predictions were comparable to literature data [Water Environ Res 1997 69 6-13)
RISK Pathogen assessment Public health authorities assess the risks of disease after exposure to environmental pathogens such as Giardia and Cryptosporidium witii methods developed for risk assessment of chemicals. But there are difficulties in using the chemical framework for assessing the risks associated with pathogens. J. Foran and the ILSI Risk Science Institute Pathogen Risk Assessment Working Group report a risk assessment conceptual framework specific to pathogens. The framework is based on the four-step
2 1 2 A • VOL. 31, NO. 5, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
