Natural attenuation of mecoprop has been studied by determining changes in enantiomeric fraction in different redox environments down gradient from a landfill in the Lincolnshire limestone. Such changes could be due to differential metabolism of the enantiomers, or enantiomeric inversion. In order to confirm the processes occurring in the field, microcosm experiments were undertaken using limestone acclimatised in different redox zones. No biodegradation was observed in the methanogenic, sulphate-reducing or iron-reducing microcosms. In the nitrate-reducing microcosm (S)-mecoprop did not degrade but (R)-mecoprop degraded with zero order kinetics at 0.65 mg l(-1)day(-1) to produce a stoichiometric equivalent amount of 4-chloro-2-methylphenol. This metabolite only degraded when the (R)-mecoprop disappeared. In aerobic conditions (S)- and (R)-mecoprop degraded with zero order kinetics at rates of 1.90 and 1.32 mg l(-1)day(-1) respectively. The addition of nitrate to dormant iron-reducing microcosms devoid of nitrate stimulated anaerobic degradation of (R)-mecoprop after a lag period of about 20 days and was associated with the production of 4-chloro-2-methylphenol. Nitrate addition to sulphate-reducing/methanogenic microcosms did not stimulate mecoprop degradation. However, the added nitrate was completely utilised in oxidising sulphide to sulphate. There was no evidence for enantiomeric inversion. The study reveals new evidence for fast enantioselective degradation of (R)-mecoprop under nitrate-reducing conditions. 相似文献
Constant and intermittent cold stressed juvenile northern bobwhite (Colinus virginianus) were exposed to chlorpyrifos, an organophosphorus insecticide, following avian dietary LC(50) test procedures. Chlorpyrifos concentrations ranged from 100 to 1000 ppm; ambient temperatures (T(a)) included 35.0 (control), 32.5, 30.0 and 27.5 degrees C. Survival decreased significantly under constant cold conditions. Non-survivors averaged 33% weight loss, but survivor weight dropped with increasing dose and decreasing T(a). Control quail at all temperatures maintained a constant body temperature (T(b)); however, T(b) of dosed quail fell with increasing dose and decreasing T(a). Non-surviving cold stressed quail had higher cholinesterase (ChE) activity that non-survivors at 35 degrees C; in addition, dead quail failed to average the 50% inhibition of ChE used to implicate a ChE depressant in death. Daily exposure of quail to 12 h of warmth increased survival. Survivors of intermittent cold stress experienced less weight loss than constant cold survivors due to reduced metabolic costs. Synergistic effects were evident in juvenile northern bobwhite exposed simultaneously to chlorpyrifos and cold stress; however, mortality and certain sublethal effects were mitigated when cold exposure was intermittent. 相似文献
The largest carbon (C) pool in United States forests is the soil C pool. We present methodology and soil C pool estimates used in the FORCARB model, which estimates and projects forest carbon budgets for the United States. The methodology balances knowledge, uncertainties, and ease of use. The estimates are calculated using the USDA Natural Resources Conservation Service STATSGO database, with soil dynamics following assumptions based on results of site-specific studies, and area estimates from the USDA Forest Service. Forest Inventory and Analysis data and national-level land cover data sets. Harvesting is assumed to have no effect on soil C. Land use change and forest type transitions affect soil C. We apply the methodology to the southeastern region of the United States as a case study. 相似文献
Investigation of a groundwater plume containing up to 24 g l(-1) phenolic compounds suggested that over a period of nearly 50 years, little degradation had occurred despite the presence of a microbial community and electron acceptors within the core of the plume. In order to study the effect of contaminant concentration on degradation behaviour, laboratory microcosm experiments were performed under aerobic and anaerobic conditions at four different concentrations obtained by diluting contaminated with uncontaminated groundwater. The microcosms contained groundwater with total phenols at ca. 200, 250, 660 and 5000 mg l(-1), and aquifer sediment that had been acclimatised within the plume for several months. The microcosms were operated for a period of 390-400 days along with sterile controls to ascertain whether degradation was microbially mediated or abiotic. Under aerobic conditions, degradation only occurred at concentrations up to 660 mg l(-1) total phenols. At phenol concentrations below 250 mg l(-1) a benzoquinone intermediate, thought to originate from the degradation of 2,5-dimethylphenol, was isolated and identified. This suggested an unusual degradative pathway for this compound; its aerobic degradation more commonly proceeding via catecholic intermediates. Under anaerobic conditions, degradation only occurred in the most dilute microcosm (total phenols 195 mg l(-1)) with a loss of p-cresol accompanied by a nonstoichiometric decrease in nitrate and sulphate. By inference, iron(III) from the sediment may also have been used as a terminal electron acceptor, in which case the amount of biologically available iron released was calculated as 1.07 mg Fe(III)/g of sediment. The study shows that natural attenuation is likely to be stimulated by dilution of the plume. 相似文献
Objective: Road accidents are an important public health concern, and speeding is a major contributor. Although flow theory (FLT) is a valid model for understanding behavior, currently the nature of the roles and interplay of FLT constructs within the theory of planned behavior (TPB) framework when attempting to explain the determinants of motivations for intention to speed and speeding behavior of car drivers is not yet known. The study aims to synthesize TPB and FLT in explaining drivers of advanced vehicles intentions to speed and speed violation behaviors and evaluate factors that are critical for explaining intention and behavior.
Method: The hypothesized model was validated using a sample collected from 354 fully licensed drivers of advanced vehicles, involving 278 males and 76 females on 2 occasions separated by a 3-month interval. During the first of the 2 occasions, participants completed questionnaire measures of TPB and FLT variables. Three months later, participants' speed violation behaviors were assessed.
Results: The study observed a significant positive relationship between the constructs. The proposed model accounted for 51 and 45% of the variance in intention to speed and speed violation behavior, respectively. The independent predictors of intention were enjoyment, attitude, and subjective norm. The independent predictors of speed violation behavior were enjoyment, concentration, intention, and perceived behavioral control.
Conclusions: The findings suggest that safety interventions for preventing speed violation behaviors should be aimed at underlying beliefs influencing the speeding behaviors of drivers of advanced vehicles. Furthermore, perceived enjoyment is of equal importance to driver's intention, influencing speed violation behavior. 相似文献
Measurements of urban air quality at monitoring stations in developed countries have frequently involved the criteria gaseous
pollutants, particulates, hazardous air pollutants, perceived air quality and relevant meteorological conditions. Large numbers
of indicators have therefore been established to quantify emissions, concentrations and environmental and human health impacts
of each of these groups of substances. To simplify the data for management, several indicators have been grouped together
to form urban air quality indices but the weightings of individual variables is contentious.
In industrialising and developing countries, data may be limited and traditional air pollutant indicators cannot often be
constructed. The emphasis therefore has to be placed on the development of policy-relevant indicators, such as Response Indicators
that reflect different policy principles for regulating air pollutant emissions. Indices that quantify the air quality management
capabilities and capacities at the city level provide further useful decision-relevant tools. Four sets of indices, namely,
1. air quality measurement capacity, 2. data assessment and availability, 3. emissions estimates, and 4. management enabling
capabilities, and a composite index to evaluate air quality management capability, were constructed and applied to 80 cities.
The indices revealed that management capability varied widely between the cities. In some of the cities, existing national
knowledge on urban air quality could have been more effectively used for management.
It was concluded that for effective urban air quality management, a greater emphasis should be given, not just to monitoring
and data capture programmes, but to the development of indicators and indices that empower decision-makers to initiate management
response strategies. Over-reliance on restricted, predetermined sets of traditional air quality indicators should be avoided. 相似文献
A field-based system used to quantify the response of acid grassland to reduced atmospheric nitrogen and sulphur deposition, and to investigate the effects of elevated soil temperature on acid grassland development is described. The system is based on 12 retractable roofs, covering undisturbed experimental plots of acid grassland and three controls. Nine roofs are used to exclude natural precipitation and three roofs used to retain emitted IR radiation at night. An irrigation system has been developed to simulate natural precipitation, allowing for the application of specific treatment regimes of ambient, reduced nitrogen and reduced nitrogen/sulphur deposition beneath the nine rain exclusion plots. Plant, soil parameters, leachate chemistry and gaseous fluxes are being monitored and initial results on soil water chemistry are described. Warming appeared to enhance nitrate concentrations in soil water but this was not sustained beyond the first year of treatment. In contrast, the deposition reduction treatments decreased soil water nitrate concentrations within a few weeks of reducing deposition. This was not observed for other solutes such as sulphate or ammonium suggesting a more direct link between deposition of nitrate and leaching losses. 相似文献