Replacement of H2O2 by O2 in Fenton and photo-Fenton reactions

The consumption of oxygen during the degradation of aniline by Fenton and photo-Fenton reactions is studied. The effect that parameters like aniline, Fe(II) and H2O2 initial concentration, pH, temperature and O2 flow rate have on the ratio O2 consumed/H2O2 consumed is examined. The determination of those combinations of experimental conditions for which an effective partial replacement of H2O2 by O2 as electron acceptor takes place is investigated. The results show that this replacement takes place in a variable extent, but the presence of H2O2 is necessary along the reaction, and the maximum consumption of O2 only takes place when the ratio amount of aniline mineralized vs. initial aniline concentration is minimal.     

Development of a sample equilibration system for the TEOM continuous PM monitor

In recent years, scientific discussion has included the influence of thermodynamic conditions (e.g., temperature, relative humidity, and filter face velocity) on PM retention efficiency of filter-based samplers and monitors. Method-associated thermodynamic conditions can, in some instances, dramatically influence the presence of particle-bound water and other light-molecular-weight chemical components such as particulate nitrates and certain organic compounds. The measurement of fine particle mass presents a new challenge for all PM measurement methods, since a relatively greater fraction of the mass is semi-volatile. The tapered element oscillating microbalance (TEOM) continuous PM monitor is a U.S. Environmental Protection Agency (EPA) PM10 equivalent method (EQPM-1090079). Several hundred of these monitors are deployed throughout the United States. The TEOM monitor has the unique characteristic of providing direct PM mass measurement without the calibration uncertainty inherent in mass surrogate methods. In addition, it provides high-precision, near-real-time continuous data automatically. Much attention has been given to semi-volatile species retention of the TEOM method.     

The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples.     

Photooxidation mechanism of nitrogen-containing compounds at TiO2/H2O interfaces: an experimental and theoretical examination of hydrazine derivatives

The photocatalytic oxidation of oxalyldihydrazide, N,N'-bis(hydrazocarbonyl)hydrazide, N,N'-bis(ethoxycarbonyl)hydrazide, malonyldihydrazide, N-malonyl-bis[(N'-ethoxycarbonyl)hydrazide] was examined in aqueous TiO2 dispersions under UV illumination. The photomineralization of nitrogen and carbon atoms in the substrates into N2 gas, NH4+ (and/or NO3-) ions, and CO2 gas was determined by HPLC and GC analysis. The formation of carboxylic acid intermediates also occurred in the photooxidation process. The photocatalytic mechanism is discussed on the basis of the experimental results, and with molecular orbital (MO) simulation of frontier electron density and point charge. Substrate carbonyl groups readily adsorb on the TiO2 surface, and the bonds between carbonyl group carbon atoms and adjacent hydrazo group nitrogen atoms are cleaved predominantly in the initial photooxidation process. The hydrazo groups were photoconverted mainly into N2 gas (in mineralization yields above 70%) and partially to NH4 ions (below 10%). The formation of NO3- ions was scarcely recognized.     

Monitoring, modelling and environmental exposure assessment of industrial chemicals in the aquatic environment

Monitoring and laboratory data play integral roles alongside fate and exposure models in comprehensive risk assessments. The principle in the European Union Technical Guidance Documents for risk assessment is that measured data may take precedence over model results but only after they are judged to be of adequate reliability and to be representative of the particular environmental compartments to which they are applied. In practice, laboratory and field data are used to provide parameters for the models, while monitoring data are used to validate the models' predictions. Thus, comprehensive risk assessments require the integration of laboratory and monitoring data with the model predictions. However, this interplay is often overlooked. Discrepancies between the results of models and monitoring should be investigated in terms of the representativeness of both. Certainly, in the context of the EU risk assessment of existing chemicals, the specific requirements for monitoring data have not been adequately addressed. The resources required for environmental monitoring, both in terms of manpower and equipment, can be very significant. The design of monitoring programmes to optimise the use of resources and the use of models as a cost-effective alternative are increasing in importance. Generic considerations and criteria for the design of new monitoring programmes to generate representative quality data for the aquatic compartment are outlined and the criteria for the use of existing data are discussed. In particular, there is a need to improve the accessibility to data sets, to standardise the data sets, to promote communication and harmonisation of programmes and to incorporate the flexibility to change monitoring protocols to amend the chemicals under investigation in line with changing needs and priorities.     

Tissue, sex and age specific accumulation of heavy metals (Zn, Cu, Pb, Cd) by populations of the mole (Talpa europaea L.) in a central urban area

Heavy metal accumulation was studied in urban populations of moles, Talpa europaea L. (Insectivora) at three sites along the "Donaukanal" in Vienna. Kidneys, liver, lung, gonads, spleen, pancreas, femur, stomach + content, heart and skin were analysed for Zn, Cu, Pb and Cd contents. Female moles showed higher Zn concentrations in spleen, gonads and skin, higher Cd concentrations in femur and stomach and lower Cu content in kidneys compared to males. Age classes were determined using teeth section. A significant increase in Cd concentration with age was found in kidneys, liver, heart, lung, skin and femur, with the highest increase for kidney samples. Pb accumulated in bone tissue (femur) with increasing age. Although significant site differences in heavy metal concentrations of soil and vegetation samples existed, these differences were only partly reflected by tissue contents.     

Modeling traffic-related air pollution in street canyons of Beijing

It is important to develop a general model to accurately simulate the air pollution in urban street areas. In this paper, the Operational Street Pollution Model (OSPM) initially developed in Denmark is tested with measured data from a relatively wide and open street in Beijing. Major factors influencing the dispersion, such as emission factors, stationary source emissions, and solar radiation, are analyzed. Results show that the model can reflect the basic dispersion pattern in the street but gives systematically higher concentrations. After modifications to estimate street-level wind speed in the model, performance is obviously improved.     

In situ monitoring of the mutagenic effects of the gaseous emissions of a solid waste incinerator in metropolitan São Paulo, Brazil, using the Tradescantia stamen-hair assay

The present work was designed to determine the potential genotoxicity at the vicinity of a solid waste incinerator in the metropolitan area of S?o Paulo, using the Tradescantia stamen-hair bioassay. Experiments were carried out between December 1998 and April 1999 in four regions (40 pots of plants per site) selected on the basis of their pollution levels predicted by theoretical modeling of the dispersion of the incinerator's plume. The exposure sites were defined as follows: highest level (incinerator); a high level (museum) located 1.5 km from the emission point; a moderate level (school, at a distance of 3.5 km from the incinerator); and a control (at Jaguariúna countryside). The difference in genotoxicity among the groups was statistically significant (p < 0.001). The frequency of mutations observed in the countryside was significantly lower [2.25 +/- 1.55, mean +/- SD (standard deviation)] than that of the sites close to the incinerator. The frequency of mutations measured at the school (3.70 +/- 1.36) was significantly lower than that measured at both the museum (4.89 +/- 1.12) and the incinerator (5.69 +/- 1.34). In conclusion, we found a positive correlation between the spatial distribution of the emissions of the incinerator located in an urban area and the mutagenic events measured by the Tradescantia stamen-hair assay. The in situ approach employed in this study was simple, efficient, and of low cost. No air or chemical extraction of pollutants was necessary for genotoxicity testing as required by other assays.     

The use of mosses and pine needles to detect persistent organic pollutants at local and regional scales

Polycyclic aromatic hydrocarbons (PAHs) were analysed in mosses (Hypnum cupressiforme) and pine needles (Pinus sylvestris) collected in the Czech Republic between 1988-94 at a regional background site in Kosetice, south Bohemia (1988-94) and two industrial sources. One industrial site (sampled 1989-91) in middle Moravia, was near a factory producing PAHs, carbon black and phthalates, the other (sampled 1991-93) near a coal and gas fuel production plant in western Bohemia. Selected chlorinated pesticides and polychlorinated biphenyl congeners were also analysed in samples at the regional background site. This study clearly shows that vegetation sampling can be used to show spatial differences in the atmospheric burden of a range of persistent organic pollutants with differences in the mixtures of compounds reflecting differences in their regional or local use/atmospheric emission.     

Seedling insensitivity to ozone for three conifer species native to Great Smoky Mountains National Park

Field symptoms typical of ozone injury have been observed on several conifer species in Great Smoky Mountains National Park, and tropospheric ozone levels in the Park can be high, suggesting that ozone may be causing growth impairment of these plants. The objective of this research was to test the ozone sensitivity of selected conifer species under controlled exposure conditions. Seedlings of three species of conifers, Table Mountain pine (Pinus pungens), Virginia pine (Pinus virginiana), and eastern hemlock (Tsuga canadensis), were exposed to various levels of ozone in open-top chambers for one to three seasons in Great Smoky Mountains National Park in Tennessee, USA. A combination of episodic profiles (1988) and modified ambient exposure regimes (1989-92) were used. Episodic profiles simulated an average 7-day period from a monitoring station in the Park. Treatments used in 1988 were: charcoal-filtered (CF), 1.0x ambient, 2.0x ambient, and ambient air-no chamber (AA). In 1989 a 1.5x ambient treatment was added, and in 1990, additional chambers were made available, allowing a 0.5x ambient treatment to be added. Height, diameter, and foliar injury were measured most years. Exposures were 3 years for Table Mountain pine (1988-90), 3 years for hemlock (1989-91), and 1 and 2 years for three different sets of Virginia pine (1990, 1990-91, and 1992). There were no significant (p<0.05) effects of ozone on any biomass fraction for any of the species, except for older needles in Table Mountain and Virginia pine, which decreased with ozone exposure. There were also no changes in biomass allocation patterns among species due to ozone exposure, except for Virginia pine in 1990, which showed an increase in the root:shoot ratio. There was foliar injury (chlorotic mottling) in the higher two treatments (1.0x and 2.0x for Table Mountain and 2.0x for Virginia pine), but high plant-to-plant variability obscured formal statistical significance in many cases. We conclude, at least for growth in the short-term, that seedlings of these three conifer species are insensitive to ambient and elevated levels of ozone, and that current levels of ozone in the Park are probably having minimal impacts on these particular species.