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41.
Emo Chiellini Andrea Corti Salvatore D’Antone Norman C. Billingham 《Journal of Polymers and the Environment》2007,15(3):169-178
Most of the standardized biodegradation tests used to assess the ultimate biodegradation of environmentally degradable polymers
are based solely on the determination of net evolved carbon dioxide. However, under aerobic conditions, it has to be considered
that heterotrophic microbial consortia metabolize carbon substrates both to carbon dioxide and in the production of new cell
biomass. It is generally accepted that in the relatively short term, 50% of the carbon content of most organic substrates
is converted to CO2, with the remaining carbon being assimilated as biomass or incorporated into humus. The latter is particularly important
when the metabolism of the organic matter occurs in a soil environment. A straightforward relationship between the free-energy
content of a carbon substrate (expressed as the standard free-energy of combustion) and its propensity for conversion to new
microbial biomass rather than mineralization to CO2 has been established. This can potentially lead to underestimation of biodegradation levels of test compounds, especially
when they consist of carbon in a fairly low formal oxidation state and relatively high free-energy content. In the present
work, the metabolism of different kind of carbon substrates, especially in soil, is reviewed and compared with our own experimental
results from respirometric tests. The results show that conversion of highly oxidized materials, such as the commonly used
reference materials, cellulose or starch, to CO2 may be significantly overestimated. The addition of glucosidic material to soil leads to greatly increased respiration and
is accompanied by a very low conversion to biomass or humic substances. In contrast, relatively less oxidized substrates metabolize
more slowly to give both CO2 and biomass to an extent which may be significantly underestimated if glucosidic materials are used as the reference. The
need for an overall carbon balance taking into account both the carbon immobilized as biomass and that volatized as CO2 must be considered in standard respirometric procedures for assessing the biodegradability of slowly degrading macromolecules. 相似文献
42.
43.
The investigation concerns the impact of the new school environment on a group of 50 male and female children aged 11–16 years, who leave home to reside temporarily at boarding school, in terms of the characteristics of problems and worries reported and the incidence of spontaneous reports of homesickness. More problems relating to the school than to the home environment were reported but proportionally more worry units were reported associated with home problems for both males and females. There was no sex differences in this respect. The reported level of spontaneously reported homesickness was 16% and there were no sex differences. Factors such as age, geographical distance of move and decision to go away to school were not influential in determining the level of reported problems or incidence of spontaneous reports of homesickness. A relationship was found with level of problems reported and recent life history but the result proved difficult to interpret. 相似文献
44.
The aerobic visible-light-photosensitised irradiation of methanolic solutions of either of the phenolic-type contaminants model compounds (ArOH) p-phenylphenol (PP), p-nitrophenol (NP) and phenol (Ph), and for two additional phenolic derivatives, namely p-chlorophenol (ClP) and p-methoxyphenol (MeOP), used in some experiments, was carried out. Employing the natural pigment riboflavin (Rf) as a sensitiser, the degradation of both the ArOH and the very sensitiser was observed. A complex mechanism, common for all the ArOH studied, operates. It involves superoxide radical anion (O2√−) and singlet molecular oxygen (O2(1Δg)) reactions. Maintaining Rf in sensitising concentrations levels (≈0.02 mM), the mechanism is highly dependent on the concentration of the ArOH. Kinetic experiments of oxygen and substrate consumption, static fluorescence, laser flash photolysis and time-resolved phosophorescence detection of O2(1Δg) demonstrate that at ArOH concentrations in the order of 10 mM, no chemical transformation occurs due to the complete quenching of Rf singlet excited state. When ArOH is present in concentrations in the order of mM or lower, O2√− is generated from the corresponding Rf radical anion, which is produced by electron transfer reaction from the ArOH to triplet excited Rf. The determined reaction rate constants for this step show a fairly good correlation with the electron-donor capabilities for Ph, PP, NP, ClP and MeOP. In this context, the main oxidative species is O2√−, since O2(1Δg) is quenched in an exclusive physical fashion by the ArOH. The production of O2√− regenerates Rf impeding the total degradation of the sensitiser. This kinetic scheme could partially model the fate of ArOH in aquatic media containing natural photosensitisers, under environmental conditions. 相似文献
45.
Mazzoleni C Kuhns HD Moosmüller H Keislar RE Barber PW Robinson NF Watson JG Nikolic D 《Journal of the Air & Waste Management Association (1995)》2004,54(6):711-726
During the spring and summer of 2000, 2001, and 2002, gaseous and particulate matter (PM) fuel-based emission factors for approximately 150,000 low-tailpipe, individual vehicles in the Las Vegas, NV, area were measured via on-road remote sensing. For the gaseous pollutants (carbon monoxide, hydrocarbons, and nitrogen oxide), a commercial vehicle emissions remote sensing system (VERSS) was used. The PM emissions were determined using a Lidar-based VERSS. Emission distributions and their shapes were analyzed and compared with previous studies. The large skewness of the distributions is evident for both gaseous pollutants and PM and has important implications for emission reduction policies, because the majority of emissions are attributed to a small fraction of vehicles. Results of this Las Vegas study and studies at other geographical locations were compared. The gaseous pollutants were found to be close to those measured by VERSS in other U.S. cities. The PM emission factors for spark ignition and diesel vehicles are in the range of previous tunnel and dynamometer studies. 相似文献
46.
47.
Singlet molecular oxygen—mediated photooxidation of monochloro and mononitrophenols. A kinetic study
A kinetic and mechanistic study on the aerobic dye sensitized photooxidation of the mono—nitro and chlorophenols was carried out. A singlet molecular oxygen mechanism operates in the photooxidation. Solvent and substituent effects, suggest the intermediacy of a complex with partial charge transfer character, as has been postulated for other phenols. Chemical (reactive) and physical interactions of the substrates with singlet molecular oxygen were discriminated. Quantum yields for photooxidation (higher for the chlorophenols) range from 3 × 10‐2 to 2 × 10‐3, as measured by substrate or oxygen consumption. These values indicate the viability of a singlet molecular oxygen photooxidation as a way for the degradation of nitro and chlorophenol environmental contaminants. 相似文献
48.
The size of particles in urban air varies over four orders of magnitude (from 0.001 μm to 10 μm in diameter). In many cities
only particle mass concentrations (PM10, i.e. particles <10 μm diameter) is measured. In this paper we analyze how differences
in emissions, background concentrations and meteorology affect the temporal and spatial distribution of PM10 and total particle
number concentrations (PNC) based on measurements and dispersion modeling in Stockholm, Sweden. PNC at densely trafficked
kerbside locations are dominated by ultrafine particles (<0.1 μm diameter) due to vehicle exhaust emissions as verified by
high correlation with NOx. But PNC contribute only marginally to PM10, due to the small size of exhaust particles. Instead
wear of the road surface is an important factor for the highest PM10 concentrations observed. In Stockholm, road wear increases
drastically due to the use of studded tires and traction sand on streets during winter; up to 90% of the locally emitted PM10
may be due to road abrasion. PM10 emissions and concentrations, but not PNC, at kerbside are controlled by road moisture.
Annual mean urban background PM10 levels are relatively uniformly distributed over the city, due to the importance of long
range transport. For PNC local sources often dominate the concentrations resulting in large temporal and spatial gradients
in the concentrations. Despite these differences in the origin of PM10 and PNC, the spatial gradients of annual mean concentrations
due to local sources are of equal magnitude due to the common source, namely traffic. Thus, people in different areas experiencing
a factor of 2 different annual PM10 exposure due to local sources will also experience a factor of 2 different exposure in
terms of PNC. This implies that health impact studies based solely on spatial differences in annual exposure to PM10 may not
separate differences in health effects due to ultrafine and coarse particles. On the other hand, health effect assessments
based on time series exposure analysis of PM10 and PNC, should be able to observe differences in health effects of ultrafine
particles versus coarse particles. 相似文献
49.
50.
Adrian C. Gleiss Serena Wright Nikolai Liebsch Rory P. Wilson Brad Norman 《Marine Biology》2013,160(11):2981-2992
Activity patterns of animals often relate to environmental variables such as food availability and predation pressure. Technological advances are providing us with new tools to monitor and better understand these activity patterns. We used animal-attached data loggers recording acceleration and depth to compare activity patterns and vertical habitat use of whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia. Whale sharks showed a moderate reverse diel vertical migration but exhibited a clear crepuscular pattern in locomotory activity. Peak activity occurred at sunset, whereas vertical movement peaked prior to this. Typical ram surface filter feeding could be identified and occurred primarily during sunset and the first hours of night. At such times, direct observations indicated whale sharks were feeding on tropical krill swarms. Kinematic analysis of postural data and data from vertical movement suggests that whale sharks at Ningaloo spend ~8 min per day actively ram surface filter feeding. Considering the high biomass present in krill schools, it is estimated that whale sharks at Ningaloo have a similar energy intake as those at other aggregation sites. Diel patterns in activity and diving behaviour suggest that whale sharks have tuned their diving behaviour in anticipation of the formation of these high-density patches which appear to only be periodically, but predictably available at sunset. Our results confirm that diel patterns in vertical habitat selection and vertical movements do not necessarily reflect patterns in activity and foraging behaviour. Direct quantification of activity and behaviour is required in gaining accurate representation of diel activity patterns. 相似文献