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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