Stable carbon and nitrogen isotope analysis of TNT: two-dimensional source identification.

Data from a combination of laboratory and fieldwork is presented to initiate testing of stable carbon and nitrogen isotope ratios to trace sources of TNT in contaminated soil and groundwater. Evaluation of these extraction methods resulted in 99.9 and 99.8% recovery of TNT with Soxhlet and solid-phase extraction (SPE), respectively. As a result of the high extraction efficiency, isotope fractionation did not occur, thus providing an accurate stable isotope value on TNT from laboratory and field samples. Subsequent experiments evaluated the stability of isotope signatures through incubations lasting up to four weeks with a 70% decline in the TNT concentration. During these experiments, no significant variation in stable carbon and nitrogen isotope ratios was measured. Five different sources of TNT, compared for stable carbon and nitrogen isotope ratios, showed a range of 4.2 and 15%, respectively. This large range in the isotope ratios suggests excellent potential to trace sources in a complex environment. Finally, a site was surveyed for concentrations and isotope values of TNT extracted from groundwaters. Values from this site were substantially different relative to the variation measured on standards and in laboratory incubation experiments. The data set indicates good potential to use stable isotopes to determine TNT sources and fate in the environment.

Effect of the fine fraction of particulate matter versus the coarse mass and other pollutants on daily mortality in Santiago, Chile.

Daily counts of non-accidental deaths in Santiago, Chile, from 1988 to 1996 were regressed on six air pollutants--fine particles (PM2.5), coarse particles (PM10-2.5), CO, SO2, NO2, and O3. Controlling for seasonal and meteorological conditions was done using three different models--a generalized linear model, a generalized additive model, and a generalized additive model on previously filtered data. Single- and two-pollutant models were tested for lags of 1-5 days and the average of the previous 2-5 days. The increase in mortality associated with the mean levels of air pollution varied from 4 to 11%, depending on the pollutants and the way season of the year was considered. The results were not sensitive to the modeling approaches, but different effects for warmer and colder months were found. Fine particles were more important than coarse particles in the whole year and in winter, but not in summer. NO2 and CO were also significantly associated with daily mortality, as was O3 in the warmer months. No consistent effect was observed for SO2. Given particle composition in Santiago, these results suggest that combustion-generated pollutants, especially from motor vehicles, may be associated with increased mortality. Temperature was closely associated with mortality. High temperatures led to deaths on the same day, while low temperatures lead to deaths from 1 to 4 days later.

Stable carbon isotope analysis of nucleic acids to trace sources of dissolved substrates used by estuarine bacteria.

The natural abundance of stable carbon isotopes measured in bacterial nucleic acids extracted from estuarine bacterial concentrates was used to trace sources of organic matter for bacteria in aquatic environments. The stable carbon isotope ratios of Pseudomonas aeruginosa and nucleic acids extracted from cultures resembled those of the carbon source on which bacteria were grown. The carbon isotope discrimination between the substrate and total cell carbon from bacterial cultures averaged 2.3% +/- 0.6% (n = 13). Furthermore, the isotope discrimination between the substrate and nucleic acids extracted from bacterial cultures was 2.4% +/- 0.4% (n = 10), not significantly different from the discrimination between bacteria and the substrate. Estuarine water samples were prefiltered through 1-micron-pore-size cartridge filters. Bacterium-sized particles in the filtrates were concentrated with tangential-flow filtration and centrifugation, and nucleic acids were then extracted from these concentrates. Hybridization with 16S rRNA probes showed that approximately 90% of the nucleic acids extracted on two sample dates were of eubacterial origin. Bacteria and nucleic acids from incubation experiments using estuarine water samples enriched with dissolved organic matter from Spartina alterniflora and Cyclotella caspia had stable carbon isotope values similar to those of the substrate sources. In a survey that compared diverse estuarine environments, stable carbon isotopes of bacteria grown in incubation experiments ranged from -31.9 to -20.5%. The range in isotope values of nucleic acids extracted from indigenous bacteria from the same waters was similar, -27.9 to -20.2%. Generally, the lack of isotope discrimination between bacteria and nucleic acids that was noted in the laboratory was observed in the field.(ABSTRACT TRUNCATED AT 250 WORDS)