RESEARCH WATCH
AIR Atmospheric partitioning Atmospheric transport and deposi tion of toxic chemicals may be strongly impacted by partitioning between the atmosphere and soil or vegetation. T. Harner and D. Mackay measured the octanol-air partition coefficient (KOA), believing it to be the physicochemical parameter that best describes this partitioning. Us ing glass wool generator columns and Tenax TA absorbent traps, they measured values of KOA at various temperatures for several chlorobenzenes, PCBs, and DDT. These were compared with values calculated using previously reported octanolwater and air-water partition coeffi cients. KOA varied log-linearly recip rocal to absolute temperature over the range of-10 to +20 °C. {Environ. Sci. Technol. 1995, 29(6), 1599-1606)
Kinetic parameters Kinetic parameters must be deter mined in designing a bioreactor for biodegrading environmental con taminants. M. Naziruddin, C.P.L. Grady, Jr., and H. H. Tabak examined the use of respirometry as a technol ogy for determining kinetic con stants for benzene and four of its chlorinated derivatives. Test sub strates of these volatile compounds were inoculated with acclimated mi crobial cultures in nutrient solution in sealed respirometry reactors. Be cause the bioreactors are sealed dur ing data gathering, respirometry is ideal for evaluating kinetic parame ters for volatile compounds. Monod and Andrews kinetic models derived kinetic constants for each com pound from oxygen uptake data. Re sults indicated that the models' quantitative data, collected automat ically, can be used to determine ki netic parameters. {Water Environ. Res. 1995, 67(2), 151-58)
BIODEGRADATION Benzene in sediments
GROUNDWATER
Highly reduced sediments, which can provide favorable colonization condi tions for sulfate-reducing organisms, present an important potential mech anism for the environment to rid itself of benzene through anaerobic degra dation. D. R. Lovley and colleagues investigated San Diego Bay, CA, anaer obic sediments for benzene degrada tion coupled with sulfate reduction. Benzene was metabolized by anaero bic sediments within 55 days of accli mation to 1 μΜ benzene; the rate in creased when more benzene was added. Radioactively labeled benzene demonstrated benzene mineralization and coupling of benzene metabolism to sulfate reduction without the ex pected extracellular metabolic inter mediates. This study is the first show ing almost complete mineralization of benzene in anaerobic, sulfate-reduc ing sediments without producing ex tracellular intermediates. {Appl. Envi ron. Microbiol. 1995, 61(3), 953-58)
Methane in groundwater sometimes is attributed to the presence of methanogenic bacteria. T. B. Parkin and W. W. Simpkins studied the high levels of methane in groundwater from the late Wisconsinan till and Wisconsinan loess of central Iowa to determine if the methane was being produced from methanogenic bacte ria in the sediment. Methane pro duction rates of the sediment gener ally followed the concentration profiles in the groundwater. The greatest production rates were asso ciated with individual pieces of wood on the loess. This indicates that buried particulate organic carbon fragments may be a signifi cant substrate for microbial growth. The authors attributed variable methane production rates to non uniform distribution of highly active microsites containing particulate
Methane production
organic carbon. The authors con cluded that methane was produced from the Pleistocene substrate. (/. Environ. Qual. 1995, 24, 367-72)
MEASUREMENTS MINIS configurations One technique currently receiving great attention for measuring trace quantities of volatile organic com pounds (VOCs) on site is membrane inlet mass spectrometry (MIMS). A series of studies demonstrate some of this technique's capabilities for new applications. Using MIMS with an ion trap and a notched wave form, R. Graham Cooks and col leagues showed that part-per-quadrillion concentrations of individual VOCs could be determined in water. Philip H. Hemberger and co-workers described a two-stage membrane coupled to an ion trap with a jet separator that can analyze VOCs at the part-per-trillion level in air. Frants R. Lauritsen and Soren Gylling used MIMS coupled with a quadrupole mass spectrometer to monitor the microbial degradation of chloroethylenes; both the decay of parent and rise of metabolite were observed at part-per-trillion levels. Tapio Kotiaho and colleagues used MIMS for on-site analysis of VOCs at the part-per-billion level in ground water at a chemical waste dump site. {Anal. Chem. 1995, 67(8), 1409-25)
Sediment bioassay The bioluminescent bacterium Photobacterium phosphoreum is widely used with sediment pore water as a bioassay for sediment toxicity. The bioassay has not been researched adequately with solid-phase sedi ment testing protocols. M. J. Benton and colleagues tested the effect on the apparent toxicity of different percentages of silt or clay in sedi ments using bioluminescent bacte ria. Increases in silt or clay content resulted in decreases in the mea sured toxicity in clean sediments
VOL. 29, NO. 7, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY • 2 9 7 A
