Photochimie et environnement - V. Photohydrolyse du monochlorobenzene en solution aqueuse diluee

A primary photohydrolysis of monochlorobenzene into phenol in dilute aqueous solution is occuring quantitatively whatever the experimental conditions were: pH (1<pH<12), excitation wavelength (253.7 nm or 300 nm), presence or absence of oxygen, initial concentration (in the range 10^?4M – 4.10^?3 M). The initial quantum yield of appearance of phenol has been found to be 0.10 ± 0.02 at 253.7 nm, and 0.19 ± 0.06 at 300 nm. The excited state leading to phenol cannot be quenched by acetonitrile at concentration up to 1.9 M. An heterolytic scission of the C-Cl bond parallels the concerted scission of water; a photosubstitution mechanism cannot account for the observed phenomena, especially in acidic media.Monofluoro- and bromobenzene irradiated in degased solution undergo a similar photohydrolysis; the initial quantum yields of appearance of phenol are 0.003 ± 0.001 and 0.06 ± 0.01, respectively for fluoro- and bromobenzene.     

The toxicity of pyrene in the fish : Synergism by piperonyl butoxide and by ultraviolet light

A saturated solution of pyrene in water was not toxic to the fish , even in the presence of ultraviolet light. A survival curve possessing one minimum, and therefore defining two LC₅₀ values, was obtained when fish placed in water containing increasing amounts of a pyrene solution in dimethylsulfoxide were exposed to ultraviolet light after a short incubation period. The phototoxicity was linked to the presence of undissolved pyrene. A normal survival curve with only one LC₅₀ value was found when pyrene was solubilized with the surfactant Tween-20. Practically no phototoxicity was produced when the pyrene mixtures were filtered before use, or when a saturated aqueous solution of pyrene was used. Piperonyl butoxide, present at a concentration where it was not toxic, synergized the toxicity of pyrene . The environmental significance of this observation may be considerable.     

An actor game on implementation of environmental quality standards for nitrogen in a Swedish agricultural catchment

Despite political efforts, diffuse pollution from agriculture continues to be the single largest source of nitrogen (N) emissions into the aquatic environment in many countries and regions. This fact, and the recent enactment of a new Swedish environmental code, led to the design of a study targeted at the evaluation of new N pollution abatement strategies. An actor game was chosen as the key component of the study, with a focus on four major goals: to test the implementability of legally binding environmental quality standards for nitrate concentration in groundwater and N transport to the sea, to find sets of agriculturally feasible and cost-effective measures to decrease N loads, to investigate the possibilities for collective action through negotiated and institutionalized actor cooperation, and to investigate the role of mathematical modeling in environmental N management. Characteristics from the agriculturally dominated catchment of Genevads?n (224 km2) on the southwest coast of Sweden served as the playing field for the actor game. The most noteworthy result from the study was that it appeared to be possible to meet ambitious environmental N standards with less economically drastic measures than anticipated by most of the participants. The actor game was shown to be a good method for learning about the new Swedish environmental code and its application and for gaining deeper insight into the issues of N management. In addition, the actor game functioned as an arena for gaining a more thorough understanding of the views of different stakeholders.     

Manganese uptake and accumulation by the hyperaccumulator plant Phytolacca acinosa Roxb. (Phytolaccaceae)

The perennial herb Phytolacca acinosa Roxb. (Phytolaccaceae), which occurs in Southern China, has been found to be a new manganese hyperaccumulator by means of field surveys on Mn-rich soils and by glasshouse experiments. This species not only has remarkable tolerance to Mn but also has extraordinary uptake and accumulation capacity for this element. The maximum Mn concentration in the leaf dry matter was 19,300 microg/g on Xiangtan Mn tailings wastelands, with a mean of 14,480 microg/g. Under nutrient solution culture conditions, P. acinosa could grow normally with Mn supplied at a concentration of 8000 micromol/l, although with less biomass than in control samples supplied with Mn at 5 micromol/l. Manganese concentration in the shoots increased with increasing external Mn levels, but the total mass of Mn accumulated in the shoots first increased and then decreased. At an Mn concentration of 5000 micromol/l in the culture solution, the Mn accumulation in the shoot dry matter was highest (258 mg/plant). However, the Mn concentration in the leaves reached its highest value (36,380 microg/g) at an Mn supply level of 12,000 micromol/l. These results confirm that P. acinosa is an Mn hyperaccumulator which grows rapidly, has substantial biomass, wide distribution and a broad ecological amplitude. This species provides a new plant resource for exploring the mechanism of Mn hyperaccumulation, and has potential for use in the phytoremediation of Mn-contaminated soils.     

Influence of air humidity on sampling efficiency of some solid adsorbents used for sampling organics from work-room air

The influence of air humidity on the sampling efficiency of Amberlite XAD porous polymers and activated charcoal was studied by determining the recovery of various organics at 20% and 85% relative humidity. The sampling efficiency of XAD-7 was found to decrease with increasing relative humidity, while the sampling efficiency of XAD-2 and activated charcoal was relatively unaffected for the compounds studied. Activated charcoal had a greater capacity than Amberlite XAD for several types of compounds, however.     

Assessing the recovery of lakes in southeastern Canada from the effects of acidic deposition

Reductions in North American sulfur dioxide (SO2) emissions promoted expectations that aquatic ecosystems in southeastern Canada would soon recover from acidification. Only lakes located near smelters that have dramatically reduced emissions approach this expectation. Lakes in the Atlantic provinces, Quebec and Ontario affected only by long-range sources show a general decline in sulfate (SO4(2-)) concentrations, but with a relatively smaller compensating increase in pH or alkalinity. Several factors may contribute to the constrained (or most likely delayed) acidity response: declining base cation concentrations, drought-induced mobilization of SO4(2-), damaged internal alkalinity generation mechanisms, and perhaps increasing nitrate or organic anion levels. Monitoring to detect biological recovery in southeastern Canada is extremely limited, but where it occurs, there is little evidence of recovery outside of the Sudbury/Killarney area. Both the occurrence of Atlantic salmon in Nova Scotia rivers and the breeding success of Common Loons in Ontario lakes are in fact declining although factors beyond acidification also play a role. Chemical and biological models predict that much greater SO2 emission reductions than those presently required by legislation will be needed to promote widespread chemical and latterly, biological recovery. It may be unrealistic to expect that pre-industrial chemical and biological conditions can ever be reestablished in many lakes of southeastern Canada.     

Concentrations and fluxes of organic compounds in the atmosphere of the Swedish west coast

Measurements of organic compounds in air and deposition have been carried out in parallel on the Swedish west coast. In this investigation the importance of long-range transport for the occurrence of organic compounds in deposition has been studied. Air samples were collected using a high volume sampler (HVS) and the deposition was sampled on a 1 m² Teflon-coated horizontal surface with runoff for the precipitation to an adsorbent. The samples were analyzed in order to identify and quantify different semivolatile compounds such as PAH and petrogenic hydrocarbons and chlorinated compounds such as PCB, HCH and HCB. Qualitative differences between the content of organic compounds in air and deposition during periods with varying levels of air pollution and different meteorological conditions have been studied and a comparison with other air pollutants, such as soot, has been carried out. The results of the measurements show that deposition of PAH and other hydrocarbons takes place continuously but the greatest amounts are measured in the deposition in connection with episodes together with heavy precipitation. The highest concentrations of PCB and HCH in the air were obtained during a warm dry period in May and the greatest amounts were deposited in a period in May with heavy precipitation.     

Two-step fast microwave-assisted pyrolysis of biomass for bio-oil production using microwave absorbent and HZSM-5 catalyst

A novel technology of two-step fast microwave-assisted pyrolysis(f MAP) of corn stover for bio-oil production was investigated in the presence of microwave absorbent(Si C) and HZSM-5catalyst. Effects of f MAP temperature and catalyst-to-biomass ratio on bio-oil yield and chemical components were examined. The results showed that this technology, employing microwave, microwave absorbent and HZSM-5 catalyst, was effective and promising for biomass fast pyrolysis. The f MAP temperature of 500°C was considered the optimum condition for maximum yield and best quality of bio-oil. Besides, the bio-oil yield decreased linearly and the chemical components in bio-oil were improved sequentially with the increase of catalyst-to-biomass ratio from 1:100 to 1:20. The elemental compositions of bio-char were also determined. Additionally, compared to one-step f MAP process, two-step f MAP could promote the bio-oil quality with a smaller catalyst-to-biomass ratio.     

Case Study Comparing Multiple Irrigated Land Datasets in Arizona and Colorado,USA

While there are currently a number of irrigated land datasets available for the western United States (U.S.), there is uncertainty regarding in how they relate to each other. To help understand the characteristics of available irrigated datasets, we compared (1) the Cropland Data Layer (CDL), (2) Moderate Resolution Imaging Spectroradiometer Irrigated Agriculture Dataset (IAD), (3) Digitized Irrigated Land (DIL), and (4) Consumptive Use for Irrigation (CUI) data in Arizona and Colorado, U.S. These datasets were derived from multiple sources at various spatial resolutions and temporal scales. We found spatial and temporal trends among all of them. The datasets showed decreases in irrigated land area in Arizona during the 2000–2010 time period. The change ranges and ratios were similar in all Arizona datasets. Irrigated land in Colorado decreased in DIL and CUI but increased in IAD and CDL. The agreement within the same type of dataset during different time periods was from 60% to 80% (R² from 0.35 to 0.72) in Arizona and from 50% to 80% (R² from 0.23 to 0.68) in Colorado. DIL had the highest agreement (80%) in both states. The agreement among different datasets acquired at approximately the same time frame ranged from 51% to 63% (R² from 0.14 to 0.31) in Arizona and from 47% to 69% (R² from 0.32 to 0.40) in Colorado. The results from this study support a greater understanding of the multiresolution and multitemporal nature of these datasets for various applications.     

Differentiating antecedents of organizational commitment: a test of March and Simon's model

Recent theory regarding the nature of organizational commitment suggests that viewing it as comprised of two dimensions, value commitment and continuance commitment, is of theoretical and practical value. This field study found the differential antecedents of these two commitment dimensions to be consistent with the March and Simon (1958) framework using the two-dimensional organizational commitment questionnaire from Mayer and Schoorman (1992). Organizational tenure, retirement benefits, education, and age were more highly correlated with continuance commitment, while felt participation, perceived prestige, job involvement, and role ambiguity were more highly correlated with value commitment. Analysis using LISREL 7 supported the pattern of relationships between the antecedents and the two commitment dimensions. © 1998 John Wiley & Sons, Ltd.