852 research outputs found
Laboratory studies of bromide oxidation in the presence of ozone: Evidence for glass-surface mediated reaction
The reaction of sodium bromide particles in the presence of ozone was studied in a flow system both under dark conditions and with 254 nm radiation. We found that there was significant formation of gaseous bromine (probably Br2) in the presence of ozone in the dark, and that bromide deposited to the walls of the Pyrex reaction flask was its source. The observed rate of gaseous bromine formation in these experiments was approximately 100–1000 times faster than expected based on the knownrate constant for aqueous reaction of bromide with ozone. While the mechanism responsible for this enhanced reactivity was not identified, based on previous reports we suggest that the glass surface converted ozone to more reactive species, such as hydroxyl radical, which in turn oxidized bromide. In the presence of 254 nm radiation, rates of gaseous bromine collection were further enhanced, likely as a result of increased radical production in the system, and wall-deposited bromide was also the source of the gaseous bromine. In these `light' experiments, there was a significant decline in ozone mixing ratios, consistent with bromine radical chemistry. These results suggest the possibility that ozone reacting with internally mixed silicate/sea-salt particles might be a significant mechanism for the oxidation of particulate halides, and subsequent release of photoactive halogen species, in the marine boundary layer
A chemical probe technique for the determination of reactive halogen species in aqueous solution: Part 1 ? bromide solutions
International audienceReactive halogen species (X*=X˙, ˙X2?, X2 and HOX, where X=Br, Cl, or I) in seawater, sea-salt particles, and snowpacks play important roles in the chemistry of the marine boundary layer. Despite this, relatively little is known about the steady-state concentrations or kinetics of reactive halogens in these environmental samples. In part this is because there are few instruments or techniques that can be used to characterize aqueous reactive halogens. To better understand this chemistry, we have developed a chemical probe technique that can detect and quantify aqueous reactive bromine and chlorine species (Br*(aq) and Cl*(aq)). This technique is based on the reactions of short-lived X*(aq) species with allyl alcohol (CH2=CHCH2OH) to form stable 3-halo-1,2-propanediols that are analyzed by gas chromatography. Using this technique in conjunction with competition kinetics allows determination of the steady state concentrations of the aqueous reactive halogens and, in some cases, the rates of formation and lifetimes of X* in aqueous solutions. We report here the results of the method development for aqueous solutions containing only bromide (Br?)
On the nucleon self-energy in nuclear matter
We consider the nucleon self-energy in nuclear matter in the absence of Pauli
blocking. It is evaluated using the partial-wave analysis of scattering
data. Our results are compared with that of a realistic calculation to estimate
the effect of this blocking. It is also possible to use our results as a check
on the realistic calculations.Comment: 6 pages, 2 figure
Photoaging of phenolic secondary organic aerosol in the aqueous phase: evolution of chemical and optical properties and effects of oxidants
While gas-phase reactions are well established to have
significant impacts on the mass concentration, chemical composition, and
optical properties of secondary organic aerosol (SOA), the aqueous-phase
aging of SOA remains poorly understood. In this study, we performed a series
of long-duration photochemical aging experiments to investigate the
evolution of the composition and light absorption of the aqueous SOA (aqSOA)
from guaiacyl acetone (GA), a semivolatile phenolic carbonyl that is common
in biomass burning smoke. The aqSOA was produced from reactions of GA with
hydroxyl radical (•OH-aqSOA) or a triplet excited state of
organic carbon (3C∗-aqSOA) and was then photoaged in water under
conditions that simulate sunlight exposure in northern California for up to
48 h. The effects of increasing aqueous-phase •OH or 3C∗
concentration on the photoaging of the aqSOA were also studied. High-resolution aerosol mass spectrometry (HR-AMS) and UV–Vis spectroscopy were
utilized to characterize the composition and the light absorptivity of the
aqSOA and to track their changes during aging.
Compared to •OH-aqSOA, the 3C∗-aqSOA is produced more
rapidly and shows less oxidation, a greater abundance of oligomers, and
higher light absorption. Prolonged photoaging promotes fragmentation and the
formation of more volatile and less light-absorbing products. More than half
of the initial aqSOA mass is lost, and substantial photobleaching occurs
after 10.5 h of prolonged aging under simulated sunlight illumination
for 3C∗-aqSOA and 48 h for •OH-aqSOA. By performing
positive matrix factorization (PMF) analysis of the combined HR-AMS and
UV–Vis spectral data, we resolved three generations of aqSOA with distinctly
different chemical and optical properties. The first-generation aqSOA shows
significant oligomer formation and enhanced light absorption at 340–400 nm.
The second-generation aqSOA is enriched in functionalized GA species and has
the highest mass absorption coefficients in 300–500 nm, while the
third-generation aqSOA contains more fragmented products and is the least
light absorbing. These results suggest that intermediately aged phenolic
aqSOA is more light absorbing than other generations, and that the light
absorptivity of phenolic aqSOA results from a competition between brown
carbon (BrC) formation and photobleaching, which is dependent on aging time.
Although photoaging generally increases the oxidation of aqSOA, a slightly
decreased O/C of the •OH-aqSOA is observed after 48 h of
prolonged photoaging with additional •OH exposure. This is likely
due to greater fragmentation and evaporation of highly oxidized compounds.
Increased oxidant concentration accelerates the transformation of aqSOA and
promotes the decay of BrC chromophores, leading to faster mass reduction and
photobleaching. In addition, compared with •OH, photoaging by
3C∗ produces more low-volatility functionalized products, which
counterbalances part of the aqSOA mass loss due to fragmentation and
evaporation.</p
The effects of claw ligatures in American lobster (Homarus americanus) storage: a preliminary study of haemolymph parameters
American lobsters are crustaceans that are offered for sale live and are stored in controlled temperature recirculating aquaria. During their marketing they are subjected to stressors that can affect their welfare, such as air exposure, confinement and handling. European legislation does not provide specific criteria or retention requirements, and so their management depends largely on the common sense of food business operators. Claw ligatures before and during storage are not legally required but are recommended because they prevent lobsters from damaging each other and ensure workers\u2019 safety. The aim of the present study is to evaluate the effect of claw ligatures on lobsters\u2019 welfare by analysing eight different haemolymph stress parameters, vitality and weight. The calcium level showed statistical differences in the two experimental groups (P < 0.05). Our results suggested that the absence of rubber bands did not offer any significant contribution to the lobsters\u2019 welfare
On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble ewline transition metals
The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM<sub>2.5</sub> samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM<sub>2.5</sub> samples approximately 80% of DTT loss is from transition metals (especially copper and manganese), while quinones account for approximately 20%. We find a similar result for DTT loss measured in a small set of PM<sub>2.5</sub> samples from the San Joaquin Valley of California. Because of the important contribution from metals, we also tested how the DTT assay is affected by EDTA, a chelator that is sometimes used in the assay. EDTA significantly suppresses the response from both metals and quinones; we therefore recommend that EDTA should not be included in the DTT assay
POLYCHLORODIBENZODIOXINS (PCDDs), POLYCHLORODIBENZO-FURANS (PCDFs), AND DIOXIN-LIKE POLYCHLOROBIPHENYLS (DL-PCBs) IN MILK, MOZZARELLA CHEESE, WHEY, AND WHEY CHEESE FROM BUFFALOES RAISED IN THE CAMPANIA REGION
Dioxins (PCDDs and PCDFs) and PCBs are a group of and toxic organo-chlorinated chemicals comprising hundreds of structurally related compounds (congeners) classified as persistent organic pollutants (POPs). It is acknowledged that 17 PCDD and PCDF congeners are of major concern due to their toxicity; 12 PCB congeners are also recognized to express dioxin-like toxicity and are thereby identified as DL-PCBs. Due to their high persistence and lipophilic nature, dioxins and PCBs tend to accumulate in fat and their bio-accumulation through the food chain may pose the risk of causing adverse effects to human health. For the general population, dietary intake is the most important pathway of exposure to the aforesaid environmental contaminants: meat, milk and dairy products, and fish and other seafood products contribute to total daily intake for more than 90 %. To prevent excessive human exposure to dioxins and DL-PCBs, the European Commission established maximum levels for dioxins and the sum of dioxins and DL-PCBs in an array of food components mainly of animal origin (Regulation EC 1881/2006). In this study, dioxins and DL-PCB concentrations were measured in buffalo milk collected from three impounded Campania farms producing milk with different contamination levels. The fate of contaminants in mozzarella cheese, whey, and whey cheese was also investigated. Analyses were carried out by HRGC-HRMS using US EPA Method 1613. The results of this study show the carry-over of the contamination from milk to its dairy products
Generation of hydrogen peroxide from San Joaquin Valley particles in a cell-free solution
Epidemiological studies have shown a correlation between exposure to ambient particulate matter (PM) and adverse health effects. One proposed mechanism of PM-mediated health effects is the generation of reactive oxygen species (ROS) – e.g., superoxide (<sup>•</sup>O<sub>2</sub><sup>&minus;</sup>), hydrogen peroxide (HOOH), and hydroxyl radical (<sup>•</sup>OH) – followed by oxidative stress. There are very few quantitative, specific measures of individual ROS generated from PM, but this information would help to more quantitatively address the link between ROS and the health effects of PM. To address this gap, we quantified the generation of HOOH by PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California during summer and winter from 2006 to 2009. HOOH was quantified by HPLC after extracting the PM in a cell-free, phosphate-buffered saline (PBS) solution with or without 50 μM ascorbate (Asc). Our results show that the urban PM generally generates much more HOOH than the rural PM but that there is no apparent seasonal difference in HOOH generation. In nearly all of the samples the addition of a physiologically relevant concentration of Asc greatly enhances HOOH formation, but a few of the coarse PM samples were able to generate a considerable amount of HOOH in the absence of added Asc, indicating the presence of unknown reductants. Normalized by air volume, the fine PM (PM<sub>2.5</sub>) generally makes more HOOH than the corresponding coarse PM (PM<sub>cf</sub>, i.e., 2.5 to 10 μm), primarily because the mass concentration of PM<sub>2.5</sub> is much higher than that of PM<sub>cf</sub>. However, normalized by PM mass, the coarse PM typically generates more HOOH than the fine PM. The amount of HOOH produced by SJV PM is reduced on average by (78 &plusmn; 15)% when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating that transition metals play a dominant role in HOOH generation. By measuring calibration curves of HOOH generation from copper, and quantifying copper concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for HOOH production by the Fresno PM. Extrapolating our results to expected concentrations of PM-derived HOOH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to cause HOOH-mediated acute health effects, but that very high PM events might lead to cytotoxic levels of pulmonary HOOH
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