PubMed · 8248790
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J J Collins. 1993-12-03. Dioxin exposure.. https://doi.org/10.1126/science.8248790
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High concentrations of H2O2 are being tested for in situ oxidation and remediation of buried organic contaminants in soils and groundwater. Peroxide is being considered as a direct chemical oxidant in Fenton-type reactions or as a source of oxidizing equivalents in bioremediation schemes. How H2O2 affects the oxidation state and solubility of Cr(III) and Cr(VI), common co-contaminants with organic chemicals, is explored here in four chemically diverse soils containing elevated levels of Cr. Soil contaminated with soluble Cr(VI) from chromite ore processing residue and soil containing high levels of recently reduced Cr (III) from electroplating waste both released dissolved Cr(VI) after single applications of up to 24 mM H2O2. In no case was there evidence that H202 reduced preexisting Cr(VI) to Cr(III), even though this would be allowed thermodynamically. Chromate in the leachates exceeded the U.S. EPA drinking water standard for total dissolved Cr (2 microM) by a factor of 10-1000. Anaerobic conditions in an organic-rich, tannery waste-contaminated soil protected Cr(III) from oxidation and mobilization. Mineral forms of Cr in serpentinitic soil near a former chromite mine also resisted oxidation on the time scale of days. Mobilization of Cr(VI) could be a hazardous consequence of using H2O2 for in situ remediation of chemically complex wastes, but H2O2 could prove attractive for ex situ treatment (i.e., soil washing). This paper demonstrates marked differences among Cr-contaminated soils in their capacity to release Cr(VI) upon chemical treatment with H2O2.
A highly sensitive, selective, and reliable analytical method has been developed and validated for characterization of asphalt fume generated under simulated road paving conditions. A dynamic asphalt fume generation system was modified to provide consistent test atmospheres at simulated asphalt road paving conditions. In the process of fume generation, asphalt was initially preheated in an oven to 170 degrees C, pumped to a large kettle, which maintained the asphalt temperature between 150 and 170 degrees C, and then transferred to the generator. The fume was conducted from the generator to an exposure chamber through a heated transfer line. Characterization of the asphalt fume test atmospheres included the following: (1) determination of the consistency of the asphalt aerosol composition within the generation system; (2) quantification of total organic matter of the asphalt fume by electron impact ionization of isotope dilution gas chromatography/ mass spectrometry); and (3) identification of individual priority polycyclic aromatic hydrocarbons (PAHs) in asphalt fume by selected ion monitoring. With the developed method, asphalt fumes could be characterized into three fractions: (1) filter collection of a large molecular size fraction over a range of mass-to-charge (m/z) ratios of 173-309; (2) XAD-2 trapping of a medium molecular size fraction over a range of m/z ratios of 121-197; and (3) charcoal trapping of a small molecular size fraction that contained mainly the volatile vapor fraction over a range of m/z ratios of 57-141. Total organic matter of the asphalt fume was quantified over the 5 exposure days. Sixteen specific priority PAHs were monitored and identified. These PAHs were determined at trace levels on the filter fraction. A novel approach, which utilizes collision-induced dissociation of fragmentation pathway leading to a characteristic fragmentation pattern by coupling microflow liquid chromatography to atmospheric pressure chemical ionization of quadrupole time-of-flight mass spectrometry, was used to further clarify the trace amount of key components present in simulated road paving asphalt fumes. These results demonstrate that asphalt fume composition could be characterized and specific priority PAHs could be identified by this method. The major advantages of this method are its highly sensitivity, selectivity, and reliability for chemical hazard characterization in a complex mixture. This method is suitable for support toxicity studies using simulated occupational exposure to asphalt fumes.
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