Novel gas exposure system for the controlled exposure of plants to gaseous hydrogen fluoride.

Plants can serve as sensitive bioindicators of the presence of contaminant vapors in the atmosphere. This work describes a novel laboratory-based gas exposure system capable of calibrating plants as bioindicators for the detection and delineation of the atmospheric contaminant hydrogen fluoride (HF) as a preparatory step for monitoring release emissions. To evaluate changes in plant phenotype and stress-induced physiological effects attributed to HF alone, the gas exposure chamber must have additional controls to simulate otherwise optimal plant growth conditions including variables such as light intensity, photoperiod, temperature, and irrigation. The exposure system was designed to maintain constant growth conditions during a series of independent experiments that varied between optimal (control) and stressful (HF exposure) conditions. The system was also designed to ensure the safe handling and application of HF. An initial system calibration introduced HF gas into the exposure chamber and monitored HF concentrations by cavity ring-down spectroscopy for a 48-h period. Stable concentrations inside the exposure chamber were observed after approximately 15 h, and losses of HF to the system ranged from 88 to 91%. A model plant species (Festuca arundinacea) was then exposed to HF for 48 h. Visual phenotype stress-induced responses aligned with symptoms reported in the literature for fluoride exposure (tip dieback and discoloration along the dieback transition margin). Fluoride concentrations in exposed tissues compared to control tissues confirmed enhanced fluoride uptake due to HF exposure. The system described herein can be applied to other reactive atmospheric pollutants of interest in support of bioindicator research.

Weathering of field-collected floating and stranded Macondo oils during and shortly after the Deepwater Horizon oil spill.

Chemical analysis of large populations of floating (n=62) and stranded (n=1174) Macondo oils collected from the northern Gulf of Mexico sea surface and shorelines during or within seven weeks of the end of the Deepwater Horizon oil spill demonstrates the range, rates, and processes affecting surface oil weathering. Oil collected immediately upon reaching the sea surface had already lost most mass below n-C8 from dissolution of soluble aliphatics, monoaromatics, and naphthalenes during the oil's ascent with further reductions extending up to n-C13 due to the onset of evaporation. With additional time, weathering of the floating and stranded oils advanced with total PAH (TPAH50) depletions averaging 69±23% for floating oils and 94±3% for stranded oils caused by the combined effects of evaporation, dissolution, and photo-oxidation, the latter of which also reduced triaromatic steroid biomarkers. Biodegradation was not evident among the coalesced floating oils studied, but had commenced in some stranded oils.

Gas emissions, minerals, and tars associated with three coal fires, Powder River Basin, USA.

Ground-based surveys of three coal fires and airborne surveys of two of the fires were conducted near Sheridan, Wyoming. The fires occur in natural outcrops and in abandoned mines, all containing Paleocene-age subbituminous coals. Diffuse (carbon dioxide (CO(2)) only) and vent (CO(2), carbon monoxide (CO), methane, hydrogen sulfide (H(2)S), and elemental mercury) emission estimates were made for each of the fires. Additionally, gas samples were collected for volatile organic compound (VOC) analysis and showed a large range in variation between vents. The fires produce locally dangerous levels of CO, CO(2), H(2)S, and benzene, among other gases. At one fire in an abandoned coal mine, trends in gas and tar composition followed a change in topography. Total CO(2) fluxes for the fires from airborne, ground-based, and rate of fire advancement estimates ranged from 0.9 to 780mg/s/m(2) and are comparable to other coal fires worldwide. Samples of tar and coal-fire minerals collected from the mouth of vents provided insight into the behavior and formation of the coal fires.

Comparative evaluation of background anthropogenic hydrocarbons in surficial sediments from nine urban waterways.

Anthropogenic hydrocarbons in surficial urban sediments derived from nonpoint sources (e.g., stormwater runoff, surface runoff, direct atmospheric deposition, and small but persistent discharges) are the principal characteristics of "urban background". Establishing the character and concentration of urban background helps determine the incremental impacts from point sources and develop successful remedial strategies. In this study, we compared the nature and amount of total extractable hydrocarbons (THC) and polycyclic aromatic hydrocarbons (PAHs), including alkylated PAHs, within 280 surficial (mostly 0-10 cm) sediments from nine, well-studied urban waterways on the East and West U.S. Coasts. These 280 sediments were predominantly impacted by urban background. All the sediments were analyzed by consistent preparation and analytical methods and met consistent data quality objectives, thereby minimizing variations attributable to methodology. The data demonstrate that the anthropogenic hydrocarbons comprising urban background from all locations exhibit a generally consistent nature, dominated by (1) a variably shaped unresolved complex mixture (UCM) within the residual (C20+) range and (2) a variable distribution of resolved 4- to 6-ring nonalkylated (parent) PAHs, mostly dominated by fluoranthene and pyrene (and exhibiting a FL/PY ratio of 0.9 +/- 0.2). The variable nature of both the THC and PAH distributions testifies that, while there is a general consistency to urban background, there are definite differences between (and even within) different urban settings. This indicates thatthere is no single "representative" urban background THC or PAH signature. The greatest mass of THC is reasonably attributable to heavy petroleum(s) comprising the UCM, whereas the greatest mass of PAHs is reasonably attributable to combustion-derived particulate matter. The mean concentration of THC attributable to urban background was 415 mg/kg (dry wt). The concentration of EPA 16-Priority Pollutant PAHs was less than 20 000 microg/kg (dry wt) in 96% of the sediments studied. Thus, sediments containing significantly more than 20000 microg/kg of the EPA 16 Priority Pollutant PAHs (or more the 30000 microg/kg of 43 parent and alkylated PAHs) should be suspected to contain PAHs not entirely attributable to urban background, unless site- or regional-specific survey data supports a different urban background concentration profile.