Distribution of metals in mechanical fractions of soils from a lake catchment in Venezuela

Soil samples were collected from both the surface and at depth from the lowlands around Lake Valencia and from the adjacent mountains. This paper reports results for Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn in mechanical fractions of the soils. Lowland soils, developed on lacustrine sediments, show a predominance of medium- to fine-grain size fractions whereas the shallow mountain soils show the highest percentage of particles in the coarse to medium fractions. Concentrations of most of the elements investigated increased toward finer particle sizes. The generally higher metal concentrations in lowland soils compared with mountain soils are consistent with release by weathering in the uplands and accumulation in the lowlands. The presence of carbonates derived from ubiquitous shelly material in the lowland soils may explain increases of Ca and Mg in labile fractions. In the lowland area, there is little evidence for the translocation of metals in the soil profiles, despite the high rainfall of a tropical climate, and the calcareous nature of these soils could account for the immobility of metals.     

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C₁₄H₁₄N₃SO₃Na) and orange II (C₁₆H₁₁N₂SO₄Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO₂ irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H₂O₂, S₂O₈²⁻) and some ions (Cl⁻, SO₄²⁻) on the process was also studied.     

Sorption, degradation, and leaching of tebuthiuron and diuron in soil columns

A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.     

Chemical degradation of chlorophenols with Fenton's reagent (Fe + H2O2)

Aqueous solutions of Fenton's reagent (Fe²⁺ + H₂O₂) have been used to effect the total decomposition of the chlorophenols: 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 3,4-dichlorophenol and 2,4,5-trichlorophenol. The mineralization of these chlorinated aromatic substrates to CO₂ and free Cl⁻ has been studied as a function of [Fe²⁺] and [HClO₄]. Increasing the concentration of Fe²⁺ enhances the decomposition process, while an increase in the concentration of HClO₄, inhibits the reaction. The presence of Fe³⁺ alone (without any Fe²⁺) with H₂O₂ has no effect on the degradation of the chlorophenols. In all cases, the stoichiometric quantity of free Cl⁻ was obtained at the completion of the decomposition reaction; but the rates of disappaearance of the chlorophenol and of the formation of the Cl⁻ are not similar. This suggests that some chlorinated aliphatic species may be formed as possible intemediates.     

Testing the extended biotic index in Slovakia: consistency, advantages, and limitations versus the saprobic assessment method of water quality.

The European Union Water Framework Directive requires the achievement of environmental objectives for the ecological quality of water bodies. A comparable implementation of the Directive throughout member countries of the European Union is necessary to verify equal protection of surface waters. The Directive specifies that member states determine ecological quality by means of biological indices. To improve comparability of water quality assessment, this research carried out an intercalibration trial between the Slovak Saprobic Index and the Italian protocol of the Extended Biotic Index, as part of a cooperative program between Italy and the Slovak Republic. When assessing streams with no or low pollution, statistics showed similar results for both methods. In contrast, the comparison of indices was not accurate in the case of severely affected waters. Reliable conversion formulas are feasible to transform the Italian Extended Biotic Index into the Slovak Saprobic Index, and not vice versa.     

Ground-level ozone mapping in large urban areas using multivariate statistical analysis: application to the São Paulo Metropolitan Area

A statistical study on the behavior of ground-level O3 concentration in different regions of a large urban area was carried out, with emphasis on pollutant gas concentrations and meteorological variables. The study was based on data generated by a network of measuring stations distributed throughout the S?o Paulo Metropolitan Area, in regions with different characteristics of traffic and economic activities. The combined application of principal component analysis and clustering techniques to data collected from 1997 until 2000 has led to the identification of implicit relationships between variables that have been associated with dominant processes related to O3 formation in different locations. Similarities between different regions of the city have also been detected and associated with local characteristics. The results indicate that the application of such statistical techniques to data collected in large urban areas enables the grouping of different regions according to their behavior in terms of O3 levels, as well as the identification of dominant processes in each group. These techniques are thus important in the planning of air pollution policies, especially in the case of O3, a pollutant that is not directly related to pollution levels alone.     

Nitration and hydroxylation of benzene in the presence of nitrite/nitrous acid in aqueous solution

This paper studies the nitration and hydroxylation of benzene in the presence of nitrite/nitrous acid in aqueous solution, both in the dark upon addition of hydrogen peroxide and under 360 nm irradiation. In both cases the detected transformation intermediates were phenol (P), nitrobenzene (NB), 2-nitrophenol (2NP) and 4-nitrophenol (4NP). P and NB directly form from benzene, and the initial formation rate of P is at least an order of magnitude higher than that of NB. In our experiments nitrophenols arise from P nitration, as can be inferred by their time evolution and isomer ratio (2NP:4NP=60:40, 3NP below detection limit). Nitrophenols may also form upon hydroxylation of NB, but in a different ratio (2NP:3NP:4NP=45:30:25). The detection of 3NP is thus a marker for the hydroxylation of NB, since this isomer is not formed in P nitration processes. The formation rates of P and NB increase with decreasing pH, both in the presence of HNO₂ + H₂O₂ in the dark (which produce HOONO) and in the presence of NO₂⁻/HNO₂ under irradiation. In the former case the pH dependence reflects the formation rate of HOONO. In the case of the irradiation experiments the pH effect can be accounted for by the higher molar absorbivity and photolysis quantum yield of nitrous acid when compared with nitrite. Interestingly, benzene does not react with HNO₂ alone in the dark. An important feature of benzene nitration in the presence of NO₂⁻/HNO₂ under irradiation is that the process is not inhibited by the addition of hydroxyl scavengers, differently from the case of phenol nitration. This finding indicates that nitrite irradiation might lead to the nitration of certain aromatic compounds in natural waters even in the presence of natural hydroxyl scavenging agents, which are usually thought to limit the environmental role of many photochemical processes.     

Comparison of different probe molecules for the quantification of hydroxyl radicals in aqueous solution

We show that the transformation of benzene into phenol is a more selective probe for the hydroxyl radical than the transformation of nitrobenzene or the generation of 4-hydroxybenzoic acid from benzoic acid. The benzene to phenol system showed adequate performance as a probe upon irradiation of lake water samples and humic acids. We show that the use of nitrobenzene and benzoic acid as hydroxyl probes should be avoided because of poor selectivity. Moreover, all the tested probe molecules underwent important interference by irradiated antraquinone-2-sulphonate, and considerably overestimated the formation of the hydroxyl radicals.     

Adsorption and desorption variability of four herbicides used in paddy rice production

This investigation was performed to determine the effect of physicochemical soil properties on penoxsulam, molinate, bentazon, and MCPA adsorption–desorption processes. Four soils from Melozal (35° 43′ S; 71° 41′ W), Parral (36° 08′ S; 71° 52′ W), San Carlos (36° 24′ S; 71° 57′ W), and Panimavida (35° 44′ S; 71° 24′ W) were utilized. Herbicide adsorption reached equilibrium after 4 h in all soils. The Freundlich L-type isotherm described the adsorption process, which showed a high affinity between herbicides and sorption sites mainly because of hydrophobic and H-bonds interaction. Penoxsulam showed the highest adsorption coefficients (4.23 ± 0.72 to 10.69 ± 1.58 mL g^?1) and were related to soil pH. Molinate showed K_d values between 1.72 ± 0.01 and 2.3 ± 0.01 mL g^?1and were related to soil pH and organic matter, specifically to the amount of humic substances. Bentazon had a high relationship with pH and humic substances and its K_d values were the lowest, ranging from 0.11 ± 0.01 to 0.42 ± 0.01 mL g^?1. MCPA K_d ranged from 0.14 ± 0.02 to 2.72 ± 0.01 mL g^?1, however its adsorption was related to humic acids and clay content. According to these results, the soil factors that could explain the sorption process of the studied herbicides under paddy rice soil conditions, were principally humic substances and soil pH. Considering the sorption variability observed in this study and the potential risk for groundwater contamination, it is necessary to develop weed rice management strategies that limit use of herbicides that exhibit low soil adsorption in areas with predisposing conditions to soil leaching.     

Neuro-fuzzy and neural network systems for air quality control

In order to define efficient air quality plans, Regional Authorities need suitable tools to evaluate both the impact of emission reduction strategies on pollution indexes and the costs of such emission reductions. The air quality control can be formalized as a two-objective nonlinear mathematical problem, integrating source–receptor models and the estimate of emission reduction costs. Both aspects present several complex elements. In particular the source–receptor models cannot be implemented through deterministic modelling systems, that would bring to a computationally unfeasible mathematical problem. In this paper we suggest to identify source–receptor statistical models (neural network and neuro-fuzzy) processing the simulations of a deterministic multi-phase modelling system (GAMES). The methodology has been applied to ozone and PM10 concentrations in Northern Italy. The results show that, despite a large advantage in terms of computational costs, the selected source–receptor models are able to accurately reproduce the simulation of the 3D modelling system.