RESEARCH WATCH
BIOREMEDIATION Mixed substrate effects Inorganic nutrients, notably phos phorus and nitrogen, typically are added to environmental matrices to stimulate bacterial growth rates and degrade target compounds. W. S. Steffensen and M. Alexander studied the effect on competition for avail able nutrients in systems containing mixtures of substrates, using benzylamine and caprolactam as the model substrates. Adding phospho rus to cultures of Pseudomonas putida enhanced benzylamine deg radation, compared to baseline lev els. Adding caprolactam and a caprolactam-utilizing strain of Ρ aeruginosa to the culture inhibited benzylamine degradation. This con dition was overcome by adding higher concentrations of phospho rus. These results indicated that the characterization of the environmen tal system relative to organic sub strates, inorganic nutrients, and mi croorganisms present must be considered prior to design. [Appl. Environ. Microbiol. 1995, 61(8), 2859-62]
Starvation promoters A common in situ bioremediation strategy for contaminated matrices involves adding nutrients to stimu late microorganism growth. High microbial growth rates and biomass concentrations often are associated with increased degradation of envi ronmental contaminants, but can be expensive to achieve, technically dif ficult to engineer and execute, and can result in undesirable biomass levels. A. Matin and colleagues used genetic starvation promoters in re combinant Escherichia coli to limit bacterial growth but maintain or en hance biodégradation levels, with trichloroethylene (TCE) and phenol as model compounds. Starvation promoters controlled the level of toluene monooxygenase synthesis, an enzyme system that degrades both TCE and phenol. Starving and
slow-growing cell suspensions degraded both, and nutrient demand was reduced by 60-90%. This work could greatly affect the engineering of biodégradation systems because starvation promoters have been cloned successfully in Pseudomonas sp. [Appl. Environ. Microbiol. 1995, 61 (9), 3323-28]
MEASUREMENTS
mass spectra with no significant differences. Three thermally labile compounds (asulam, thiodicarb, and thiofanox) could not achieve spectra consistency. The authors attributed this to difficulties in standardizing vaporizer conditions rather than differences in ion-source geometry. Differences in the mass spectra of carbofuran, however, reflected differences in ion source geometry. [}. Am. Soc. Mass Spectrom. 1995, 6(8), 656-67]
Phthalates in sediments
Pesticide stability
Phthalate esters are used as nonreactive plasticizers, which can migrate from plastic products into aquatic environments. M. D. Williams and colleagues studied the accuracy of experimental determination of partition coefficients of four phthalate esters. The Freudlich equation reasonably described sediment partition coefficients for the phthalate esters, but the partition coefficient decreased as the particle concentration increased. The authors postulated that this resulted from either complexation of phthalates to dissolved organic carbon or particle-induced adsorption. The experimental partition coefficients were 1 to 3 orders of magnitude lower than those estimated from the octanol-water partition coefficient. The authors suggest that sediment pore-water concentration estimates are likely to be overstated if partition coefficients are not corrected for the effects of solids. [Environ. Toxicol. Chem. 1995, 14(9), 1477-86]
Transporting the sample from the field to the lab for analysis complicates monitoring of water samples for pesticides. Solid-phase extraction (SPE) can greatly reduce the size and weight of samples to be transported; however, questions remain concerning the stability of pesticides stored on SPE disks. S. A. Senseman and colleagues studied the stability of 12 pesticides of varying physical and chemical properties on SPE disks stored at ambient or frozen temperatures following four desiccation procedures. Results from storage temperature experiments showed that frozen storage was preferable. Desiccation results were mixed. For example, freeze-drying efficiently removed components susceptible to water-stabilizing hydrolysis but increased chromatographic noise and loss of a more volatile component. [Anal. Chem. 1995, 67(17), 3064-68]
Thermospray spectra Thermospray (TSP) has been used as a liquid chromatography-mass spectrometry interface in measuring carbamate pesticides, but reports in the literature have not shown consistent mass spectra. D. Volmer and colleagues studied the influence of ionsource geometry for 16 carbamate pesticides with three different TSP interfaces. They found that controlling the experimental parameters for 12 of the 16 pesticides could lead to
POLICY The Mexican environment The North American Free Trade Agreement has increased concerns over environmental issues in Mexico, especially at the U.S. border. L. Babcock and P. Nieder present a national overview of the demographic and physical environment of Mexico. No comprehensive environmental survey of Mexico exists. Environmental impact assessments also are new to the country. Mexican envi-
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ronmental laws date to 1940, though until the current administration, environmental regulations were enforced by large agencies that also oversaw development as well. Understanding how the Mexican situation is different from those of the U.S. and Canada will help manage environmental issues in Mexico and at the border. [The Environmental Professional 1995, 17(2), 137-52]
Decision-analytic tests To manage an ecosystem, appropriate data must be gathered that establish the significance of biological effects of a stressor. M. Power and colleagues showed that the most popular statistical tests of significance are designed to draw conclusions about a system, rather than aid in management decisions. Conclusion-drawing tests have two drawbacks: They require strong evidence about the system, because conclusions will be accepted as truth, and popular statistical tests ignore the consequences of decisions on the tests. The authors conclude that decision-analytic tests avoid these drawbacks, improving the ability of environmental managers to implement cost-effective strategies based on available knowledge. [Environ. Manage. 1995, 79(5), 629-39]
REMEDIATION Vapor extraction Vapor extraction of contaminated soils removes volatile hydrocarbons and, to a lesser extent, enhances in situ biodégradation of hydrocarbons. Decreased soil moisture content, increased soil temperature, substrate removal, and soil gas level variations affect in situ biodégradation during vapor extraction. W. J. Hickey studied vapor extraction in a gasoline plume, observing substantial reduction of the gasoline fraction and microbial activity within the first 60 days. Although soil moisture content decreased and temperature increased during vapor extraction, microbial activity decreased. Hickey attributed this to preferential removal of the lower molecular weight gasoline fraction. Gasoline vapor reaccumulation was not maximized until two or three months after the vacuum stopped. Results indicate that monitoring soil vapor concentrations within the first few weeks
after the termination may not provide an accurate assessment of soil remediation. (/. Environ. Qual. 1995, 24, 571-82)
RISK Comparative risk limits E. Silbergeld studied the scientific and social limitations inherent in comparative risk assessment. Comparative risk assessments are weakened by the multifactorial nature of risk, voluntary versus involuntary exposures, and comparisons of cancer versus noncancer endpoints. She proposes reforms, including standardized risk methodology for noncancer endpoints, improved and ensured public access to risk debates, and increased health effects data collection and analyses. [New York University Environmental Law Journal 1995, 3(2), 405-30]
SEDIMENTS Pore-water methods Sediment pore-water collection methods can significantly influence analysis results. N. Sarda and G. A. Burton, Jr., studied four pore-water collection methods to ascertain the effect on ammonia analysis. They collected sediments using a hand corer with a 5-cm diameter dredge and a standard 15.5-cm2 Ekman dredge. Pore-water was extracted from each sediment sample using centrifugation. Pore-water also was directly sampled in the field using a suction technique and a "peeper" method involving sample jars fitted with mesh. The hand corer and Ekman dredge resulted in the highest pore-water ammonia concentrations for all three study sites. The authors conclude that these methods could result in artificially elevated porewater chemical analyses. [Environ. Toxicol. Chem. 1995, 14&), 1499-506]
WASTEWATER Wetlands treatment Several parameters must be considered when designing an effective constructed wetlands for wastewater treatment, such as the effects of plant types and draining, system ki-
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netics, aerobic and anaerobic respiration contributions to biochemical oxygen demand (BOD) removal, and characterization of oxygen transport effects. P. S. Burgoon and colleagues evaluated these parameters for a subsurface flow wetlands under batch and continuous flow conditions. Pilot-scale wetlands were constructed and subjected to primary or secondary wastewater. Plants enhanced the removal of carbonaceous and nitrogenous BOD but increased hydraulic retention times (HRT). Periodic draining did not affect BOD removal. BOD removal kinetics were first order for HRT of less than 24 h. Oxygen transport through plants did not significantly affect BOD removal at > 24 h HRT. Methanogenesis was found to be a major respiratory pathway for BOD removal. [Water Environ. Res. 1995, 67(5), 855-62]
Removing heavy metals Heavy metal concentrations
