ASSESSMENTS Pesticides and plants To predict exposure of wildlife to pesticide residues in plants, EPA uses a simple linear relationship de­veloped in the 1970s (the Kenaga nomogram). John Fletcher and co­workers from the University of Okla­homa and EPA have reevaluated the accuracy of these estimates by com­paring recent measured residue lev­els with predictions made with the EPA method. Generally the nomo­gram is conservative in its predic­tions, with actual values exceeding predictions in 7.8% of the cases ex­amined. The authors recommend increasing predicted values for for­age and fruit by threefold and con­densing the number of plant catego­ries from six to four. (Environ. Toxicol. Chem. 1994, 13(9), 1383-91)

BIODEGRADATION

Anaerobic degradation Heterocyclic compounds tend to be more polar and water soluble than their homocyclic counterparts. Therefore, they have a greater poten­tial for transport to anoxic subsur­face aquifers. Neal Adrian and Jo­seph Suflita of the University of Oklahoma have studied the anaero­bic biodégradation of a series of het­erocyclic compounds (pyridines, pyrimidines, uracils, triazines, furans, and thiophenes) and their halogenated and carboxylated ana­logs in anoxic aquifer slurries. Ex­cept for pyrimidine, the nonsubsti-tuted heterocyclics studied tended to resist anaerobic biodégradation. Adding carboxyl groups to the ring tended to increase the rate of bio-degradation, whereas the addition of a halogen reduced or precluded the rate of biodégradation. Brominated compounds did, however, show more mineralization than did their chlorinated analogs. (Environ. Toxi­col. Chem. 1994, 13, 1551-57)

Long-term PCB data from air filters It has been established that polvchlorinated biphenyls (PCBs) are spread through­out the globe by atmospheric transport processes. Models of these processes suggest that volatilization from past inputs to soil and water can occur and could influence current control strategies. The effectiveness of these strategies can be evaluated with long-term environmental trend data. Kevin Jones and colleagues at Lancaster University and AEA Technology (U.K.) have provided a consistent long-term data set from a single site in the United Kingdom. From yearly mea­surements taken since 1972, they determined the PCB concentration in a set of air filters. Although the filters had been stored at room temperature, the results showed total PCB on the particulates declined by a factor of 4.6-4.7 between the 1972-1976 and 1987-1992 averages. Contemporary particulate/vapor ratios and total suspended particulate data (contemporary and historical) were used to esti­mate total atmospheric PCB over the period studied. The rate of decline was greatest in the earlier years and has been much slower in recent times (Environ. Sci. Technol., this issue, p. 272).

Plastic films Competition for available landfill space for waste plastic films in the United States has catalyzed the de­velopment of degradable plastic film products. The need for more stan­dardized measurement techniques with which to evaluate the environ­mental fate of these products is criti­cal in defining and characterizing their degradability claims. Asha Ya-bannavar and Richard Bartha of Rut­gers University have tested and com­pared traditional and novel techniques for evaluating these claims.

Photosensitized polyethylene (PE), starch-PE, extensively plasti-cized polyvinyl chloride, and poly­propylene films were incorporated into aerobic soil and their biodégra­dation evaluated for three months. C02 evolution, residual weight re­covery, loss of tensile strength, gas chromatography, and gel permeation chromatography (GPC) were the methods used for evaluation. C02

evaluation was adequate for screen­ing plastic film biodégradation, but confirmation of polymer degrada­tion by GPC was recommended for films with additives. (Appl. Environ. Microbiol. 1994, 60, 3608-14)

BIOREMEDIATION

TCE degradation Trichloroethylene (TCE) exhibits en­vironmental toxicity, is recalcitrant to microbial degradation, and is a widespread environmental contami­nant. Pseudomonas cepacia G4 is a microorganism that can degrade TCE in the presence of toluene. An­drew Landa and colleagues at the University of Groningen describe the kinetics of TCE degradation by this organism in a chemostat, as well as the effect of high concentrations of TCE on cell growth and TCE trans­formation.

The efficiency of TCE conversion decreased when the TCE loading was elevated from 7 to 330 pmol/L/h. The utilization of toluene and cell yield were not affected at TCE load­ing rates of up to 145 pmol/L/h. The paper presents a kinetic model that can be applied to bioreactor design. The results demonstrate that Ρ cepa­cia G4 can be used in a bioreactor designed to degrade TCE and that this organism is more resistant to shock loadings of TCE than are other organ­isms studied to date. (Appl. Environ. Microbiol. 1994, 60, 3368-74)

1 0 A • VOL. 29, NO. 1, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 0013-936X/95/0929 10A$09.00/0 © 1994 American Chemical Society

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