Pentachloronitrobenzene is a fungicide that is degraded in anoxic soils and sediments through unknown processes that are often thought to be biologically mediated. The present research describes the kinetics for the abiotic reduction of this compound in aqueous Fe(II)/goethite systems at near-neutral pH values. The results provide evidence for a rate-affecting surface-association process rather than a direct (i.e., kinetically second-order) reaction with an adsorbed Fe(II) species. It is therefore likely that the iron oxide surface participates directly in the reaction. Furthermore, reduction is observed in the apparent presence of trace amounts of suspended iron oxide nanoparticles, formed in situ by the oxidation of Fe(II). Given that Fe(III) colloids and other nanoscale phases may occur in natural sediments, such abiotic reactions could significantly influence the environmental fate of nitroaromatic compounds.
The herbicide trifluralin (2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine) is widely used in agriculture and may pose toxic risks to some aquatic organisms. While its degradation has been investigated in field studies, this research is the first to elucidate the specific abiotic transformations that trifluralin may undergo in reducing environments such as flooded soils and wetland sediments. Kinetic data and product identities were determined for the degradation of trifluralin in Fe(II)/goethite suspensions at near-neutral pH values. Under these conditions, trifluralin is consumed rapidly through a surface-mediated process that includes three distinct reactions: reduction of nitro groups, dealkylation of propylamines, and cyclization to form benzimidazoles. All detected products are among those that have been reported in natural soils and sediments. Therefore, these transformation pathways may play a significant role in affecting the fate of trifluralin in the environment.
Little cigar mainstream smoke is less well-characterized than cigarette mainstream smoke in terms of chemical composition. This study compared four popular little cigar products against four popular cigarette products to determine compounds that are either unique to or more abundant in little cigars. These compounds are categorized as new or distinctive exposures, respectively. Total particulate matter samples collected from machine-generated mainstream smoke were extracted with methylene chloride, and the extracts were analyzed using two-dimensional gas chromatography–time-of-flight mass spectrometry. The data were evaluated using novel data-processing algorithms that account for characteristics specific to the selected analytical technique and variability associated with replicate sample analyses. Among more than 25 000 components detected across the complete data set, ambrox was confirmed as a new exposure, and 3-methylbutanenitrile and 4-methylimidazole were confirmed as distinctive exposures. Concentrations of these compounds for the little cigar mainstream smoke were estimated at approximately 0.4, 0.7, and 12 μg/rod, respectively. In achieving these results, this study has demonstrated the capability of a powerful analytical approach to identify previously uncharacterized tobacco-related exposures from little cigars. The same approach could also be applied to other samples to characterize constituents associated with tobacco product classes or specific tobacco products of interest. Such analyses are critical in identifying tobacco-related exposures that may affect public health.
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