Comparison of metastable atom bombardment and electron capture negative ionization for the analysis of polychloroalkanes

A new method for quantifying C10-C13 polychloroalkanes (PCAs or chloroparaffins, CPs) in environmental samples using metastable atom bombardment ionization (MAB) and high resolution mass spectrometry is presented. Contrary to electron capture negative ionization (ECNI), MAB can produce spectra for molecules having a low number of chlorine atoms. These molecules are present in commercial PCAs and are responsible for a large fraction of the total PCA concentration in water samples analysed. Using ECNI or MAB, no molecular ion can be seen in the spectra. ECNI spectra contain important peaks corresponding to [M-Cl]- and [M-HCl]-* while the base peak in MAB spectra is [M-Cl]+ with no [M-HCl]+* present. The mass range for C10-C13 CPs is very large and scanning the masses for all the compounds involved would lead to a loss of sensitivity. Two chromatographic analysis are thus performed using high resolution selective ion monitoring with only a limited number of masses recorded per run. To reduce analysis time, a short capillary column is used. Application of this method to the analysis of high-volumes water samples (dissolved and particulates portions separately) from the St. Lawrence river near Quebec City using MAB is presented. Contribution of molecules with a low chlorine content in the samples account for between 10% and 46% to the total concentration. Congeners distribution between the different fractions indicates that molecules with a low number of carbon atoms are preferentially retained on the particulates. Within a carbon number group, there is a slight tendency to accumulate molecules with a high number of chlorine atoms in the dissolved fraction.     

A multiobjective optimization framework for multicontaminant industrial water network design

The optimal design of multicontaminant industrial water networks according to several objectives is carried out in this paper. The general formulation of the water allocation problem (WAP) is given as a set of nonlinear equations with binary variables representing the presence of interconnections in the network. For optimization purposes, three antagonist objectives are considered: F(1), the freshwater flow-rate at the network entrance, F(2), the water flow-rate at inlet of regeneration units, and F(3), the number of interconnections in the network. The multiobjective problem is solved via a lexicographic strategy, where a mixed-integer nonlinear programming (MINLP) procedure is used at each step. The approach is illustrated by a numerical example taken from the literature involving five processes, one regeneration unit and three contaminants. The set of potential network solutions is provided in the form of a Pareto front. Finally, the strategy for choosing the best network solution among those given by Pareto fronts is presented. This Multiple Criteria Decision Making (MCDM) problem is tackled by means of two approaches: a classical TOPSIS analysis is first implemented and then an innovative strategy based on the global equivalent cost (GEC) in freshwater that turns out to be more efficient for choosing a good network according to a practical point of view.     

Functional autoregressive forecasting of long-term seabed evolution

There is a need for decadal predictions of the seabed evolution, for example to inform resurvey strategies when maintaining navigation channels. The understanding of the physical processes involved in morphological evolution, and the viability of process models to accurately model evolution over these time scales, are currently limited. As a result, statistical approaches are used to supply long-term forecasts. In this paper, we introduce a novel statistical approach for this problem: the autoregressive Hilbertian model (ARH). This model naturally assesses the time evolution of spatially-distributed measurements. We apply the technique to a coastal area in the East Anglian coast over the period 1846 to 2002, and compare with two other statistical methods used recently for seabed prediction: the autoregressive model and the EOF model. We evaluate the performance of the three methods by comparing observations and predictions for 2002. The ARH model enables a reduction of 10% of the root mean squared errors. Finally, we compute the variability in the predictions related to time sampling using the jackknife, a method that uses subsamples to quantify uncertainties.     

Impact of repeated irrigation of lettuce cultures with municipal wastewater on soil bacterial community diversity and composition

Environmental Science and Pollution Research - The effect of wastewater irrigation on the diversity and composition of bacterial communities of soil mesocosms planted with lettuces was studied over...     

Aqueous solubility and n-octanol/water partition coefficient correlations

Studies of the fate of chemicals require the knowledge of numerous parameters, among which of utmost importance are the water solubility and the n-octanol/water partition coefficient.

Numerous writers have demonstrated that there is a close correlation between these two parameters. The literature offers about fifteen cases of correlations between solubility and n-octanol/water partition coefficient with, for some of them, and for solids, a third variable: the fusion point. Unfortunately, the coefficients are often the results of theoretical considerations and the size of the data base is often small.

A study carried out on 300 products shows clearly the importance of the size of the data base. It is demonstrated that the coefficients obtained in practice are different from those which had been calculated theoretically. In particular, the introduction of a fusion point correction appears to be justified only to a limited extent.

This analysis has shown that there is a need to reexamine the theoretical approach and determine why the coefficients of the regression equation do not appear to adopt the values excepted from theoretical considerations.     

Photochimie et environnement X- evaluation de la toxicite des produits de phototransformation de l'hydroquinone et des chlorophenols en milieu aqueux

A test of acute toxicity on DAPHNIA MAGNA is suggested to evaluate the efficiency of the phototransformation as a route of abiotic degradation. This test is recommended for compounds phototransformed into a complex mixture of products. Hydroquinone, 2-chloro-, 4-chloro-, 2,4-dichloro-, 2,4,6-trichloro- and pentachlorophenol were studied as examples. In any case the phototransformation is an useful depollution technique on condition the irradiation to be completed as far as the ultimate step of phototransformation.     

Termite assemblages in a West-African semi-deciduous forest and teak plantations

Responses of termite assemblages to the conversion of semi-deciduous forest into teak plantations were studied in the Lama Forest Reserve in Benin, West Africa. Four belt transect surveys were run in each of the two forest types, adopting a modified termite diversity assessment protocol. Termite assemblages were remarkably species-poor in both forest types, with only 19 species encountered altogether. The low species richness was due to the rarity of soil-feeders of the soil/humus interface and the absence of true soil-feeders in the compact vertisol soil. Species richness was significantly higher in semi-deciduous forest than in teak plantations, but termite encounters were significantly lower. Termite assemblage and feeding group structure differed significantly among forest types. Wood-feeders were recorded only in semi-deciduous forest. In contrast, fungus-growers were more species-rich and about four times more abundant in teak plantations, mainly due to one Ancistrotermes species. The humification score, which depicts the position of termite assemblages along a gradient of increasing humification of their food substrate, was significantly higher in teak plantations, due to the absence of wood-feeders and the preponderance of fungus-growers. Combined principal components and multiple regression analysis identified two significant predictors of termite assemblages, soil water content and leaf litter biomass. The abundance of fungus-growers in teak plantations seemed to be mainly related to the high leaf litter biomass. Indirect evidence also suggests that lower predation pressure by ants on termites in teak plantations may have contributed to the abundance of termites.     

Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed.     

Effects of surfactant and temperature on biotransformation kinetics of anthracene and pyrene

The biotransformation and mineralization of a mixture of two polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, which are known contaminants of soil and groundwater, by an enrichment culture in the presence or absence of 100 mg l(-1) Tergitol NP-10, a non-ionic surfactant, and at temperatures of 10 degrees C and 25 degrees C were investigated. The overall biotransformation of 2 mg l(-1) total PAHs with free cell suspensions in batch culture was greater than 97.2% at both examined temperatures. At 25 degrees C, the overall mineralization of anthracene was 48.8% and that of pyrene was 66.1%. However, the decrease of temperature to 10 degrees C had a negative effect on the mineralization of PAHs and reduced it to 18.5% and 61.5% for anthracene and pyrene, respectively. Using a higher PAHs concentration of 20 mg l(-1) at 25 degrees C, the overall biotransformation of anthracene was 80.7% and that of pyrene was 100%, where only 17.3% anthracene and 7.6% pyrene were mineralized to carbon dioxide and water. The addition of surfactant at 25 degrees C increased the overall mineralization of anthracene and pyrene to 33.0% and 27.6%, respectively. However, the addition of surfactant at 10 degrees C had a negative impact on the overall biotransformation of anthracene and pyrene, reducing them to 20.6% and 14.0%, respectively. These results have significant implications in the bioremediation of PAHs-contaminated sites.