Pyrene measurements in sooting low pressure methane flames by jet-cooled laser-induced fluorescence.

This paper presents in detail the study we carried out concerning the pyrene measurement by jet-cooled laser-induced fluorescence (JCLIF) in different sooting low pressure methane flames. The aim of this paper is both to demonstrate the potentialities of this technique for the measurement of such moderately sized polycyclic aromatic hydrocarbons under sooting flame conditions and to provide new experimental data for the understanding and the development of chemical models of the soot formation processes. Several concentration profiles of pyrene measured in different sooting flame (various pressure and equivalence ratio) are presented. The validation of the JCLIF method for pyrene measurements is explained in detail as well as the calibration procedure, based on the standard addition method, which has been implemented for the quantification of the concentration profiles. Sensitivity lower than 1 ppb was obtained for the measurement of this species under sooting flame conditions.

High-resolution profiles of trace metals in the pore waters of riverine sediment assessed by DET and DGT.

The techniques of DET (diffusive equilibrium in thin films) and DGT (diffusive gradients in thin films) were applied to obtain high-resolution vertical profiles of trace metals in freshwater sediments. In the framework of the EU-Interreg project Stardust (http://www.vliz.be/projects/stardust/) between France and Belgium, in which the mobility of sediment bound metals is investigated, sediment samples were collected from the Upper Scheldt River (at Helkijn, Belgium) and the Leie River (at Warneton, located at the Belgian-French border). Intra- and inter-laboratory comparisons of the gel techniques were carried out between the two laboratories involved. In general, a good agreement was observed, taking sediment heterogeneity into account. At both stations, metal pore water profiles show more or less similar tendencies although the sediment at Warneton was more anoxic than at Helkijn. A strong correlation between Fe and Co was found at Helkijn as well as at Warneton. The metal gradients at the water/sediment interface were calculated from the high resolution profiles and the conventional, low resolution profiles. Significant differences were observed.

Use of constrained DET probe for a high-resolution determination of metals and anions distribution in the sediment pore water.

The constrained DET (diffusive equilibrium in thin films) probe filled with agarose gel was successfully used for measuring depth profiles of metals and anions in estuarine sediments at high-resolution (mm). The agarose gel was tested for equilibration times and recoveries. For manganese (10 mg l(-1)), the equilibration time between an aqueous solution and the agarose gel was reached after 60 min. In the presence of humic acids it was five times longer. As a consequence, for field applications a deployment time of 5-24 h was applied. The subsequent elution of manganese into nitric acid was completed in less than 10 min even without mixing. For agarose gel in contact with solutions of 10 mg l(-1) ions (cadmium, copper and manganese, bromide, chloride, nitrate and sulfate), recoveries obtained were close to 100%. DET probes were applied in test laboratory sediment and in real sediment in the Authie (France) estuary. Depth profiles for 19 elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Sr, Tl, V, and Zn) and four anions (bromide, chloride, nitrate and sulfate) were established for the test laboratory sediment. In the real sediment, the pore water concentrations of iron and manganese using gel probes were comparable with those obtained by a conventional method (box core-anoxic slicing followed by centrifugation).

Distribution of iron and manganese in the Seine river estuary: approach with experimental laboratory mixing.

The physico-chemical behaviour of iron and manganese has been observed during many surveys covering various hydrodynamic conditions in the Seine river estuary system. The results obtained confirm the non-conservative behaviour of these two metals. Generally, dissolved iron exhibits non-conservative removal and shows a rapid decrease in low salinity; it is moved from fresh waters with high concentrations to saline waters with very low concentrations. This can be attributed to the flocculation processes as confirmed by laboratory experiments. Dissolved manganese versus salinity curves exhibit a peak concentration in the low salinity zone. Laboratory mixing experiments have been undertaken comparing iron and manganese adsorption/desorption from suspended material versus salinity, using a series of water samples collected in the up-river and marine regions in order to assess the importance of particulate material and salinity on iron and manganese distributions. The salinity was controlled by varying the marine to fresh water ratio. The reaction kinetics aspect is developed in more detail for manganese in the last series of remobilization experiments starting from a stock of suspended particles collected in the upstream river site (Caudebec) in mixtures of waters, according to time and salinity. This study has allowed us to show that iron and manganese behaviour in the Seine estuary is strongly influenced: (i) by the high turbidity zone and by the presence of calcium carbonate which could stabilise the Mn(II) form; and (ii) by the increase of salinity, calcium, magnesium and suspended matter concentrations and by complex formation.

[Nitrate contamination of the groundwater of the Akkar Plain in northern Lebanon]. / Contaminaltion par les nitrates des eaux souterraines de la plaine d'Akkar au Liban du Nord.

The Akkar Plain in northern Lebanon covers an area of 130 km2 and is the second largest agricultural region in the country. It also borders the Mediterranean Sea (Figure 1). Groundwater supplies are the only source of drinking water in this region and there is no public drinking water network. This area has a population of about 75,000 inhabitants, who have depended on and used the water from these aquifers for many years, with no treatment, filtration or monitoring system in place. The inhabitants and farmers depend on groundwater supplies for crop irrigation and other uses. The plain provides ideal conditions for agriculture and the use of chemical fertilizers has been increasing. Over-fertilization, resulting in the application of excess nitrogen, and the lack of vegetation during the winter have disturbed the nitrogen cycle, leading to the pollution of groundwater supplies with high concentrations of nitrate. Nitrates seep slowly into the soil at a rate of about 0.5 to 1 meter per year until they reach the water table. However, tons of nitrogen are carried into the groundwater each year by runoff and infiltration. If a water source is found to be heavily contaminated with nitrate, it is probably too late and too difficult to correct the problem within a short period of time. Corrective measures may not be effective, as shown by current high nitrate concentrations despite previous efforts to resolve the problem. Therefore, we must try to keep nitrate levels within acceptable limits. If action is not taken now, future generations will pay the price of current bad practice in agriculture. International water quality guidelines permit a maximum of 50 mg nitrates/l for adults and of 25 mg/l for infants and pregnant women. The intake of nitrates in drinking water by humans is currently one of the major environmental problems associated with agricultural practice. Nitrate is itself inert but concern arises due to its possible conversion into nitrite, which is highly toxic. We analyzed the nitrate content of water samples from 15 private wells currently used for human consumption and agricultural in an effort to deal with the nitrate pollution of groundwater supplies in the Akkar Plain. We found that 14 of the 15 wells had a nitrate concentration above 50 mg/l, with a maximum of 163 mg/l. In addition, salt water was found to have contaminated groundwater supplies in some of the villages along the coastline in the north. Our results indicate that the groundwater is seriously contaminated with nitrates, to the extent that it does not meet international drinking water standards. These high nitrate levels may have adverse effects and cause disease. The toxic effects of nitrate contamination are most severe in individuals with weak immune systems, such as the elderly and children. We are currently developing solutions and preventive measures for this extremely worrying situation, based on these data.

Chemical and electrochemical behaviour of nitric and nitrous acids in sulpholane.

With a glass electrode filled with mercury as indicator electrode for hydrogen ions, the acidity constant of nitric acid and the stability constants of the complexes HA(-)(2) (A Cl(-), NO(-)(3)) in sulpholane at 303 K have been determined potentiometrically. The acidity constant of nitrous acid has also been determined in supholane medium because of the low stability of this acid in aprotic media. On the basis of the results, some aspects of the electrochemical and thermodynamic properties of oxygen-nitrogen compounds are discussed in order to explain the catalytic effect of NO(+) in aromatic nitration by N(2)O(4) and/or N(2)O(3) in aprotic solvents.

[Not Available]. / Comportement electrochimique du tetraoxyde de diazote dans le sulfolane.

Knowing the values of the equilibrium constants corresponding to the reactions N(2)O(4) right harpoon over left harpoon 2NO(2) and N(2)O(4) right harpoon over left harpoon NO(+) + NO(3)(-) in sulpholane, we have undertaken the electrochemical study of N(2)O(4) by means of linear and cyclic voltammetry at the platinum electrode. The N(2)O(4) species undergoes one oxidation step N(2)O(4) right harpoon over left harpoon 2NO(2) right harpoon over left harpoon 2NO(2)(+) + 2e and two reduction steps NO(2) + N(2)O(4) + e(-)right harpoon over left harpoon N(2)O(3) + NO(3)(-) (1st wave), followed by 3N(2)O(4) + 2e(-) right harpoon over left harpoon 2N(2)O(3) + 2NO(3)(-), N(2)O(4) + e(-) right harpoon over left harpoon NO + NO(3)(-), 2N(2)O(3) + e(-) right harpoon over left harpoon 3NO + NO(3)(-) (2nd wave). The redox properties of N(2)O(4) are complicated by trace quantities of water because of the formation of the electroactive species N(2)O(3), HNO(3) and HNO(2) according to N(2)O(4) + H(2)O right harpoon over left harpoon HNO(2) + HNO(3) and N(2)O(4) + HNO(2) right harpoon over left harpoon N(2)O(3) + HNO(3). The standard potentials of the couples concerned have been evaluated and are discussed. sont discutés et évalués.

[Not Available]. / Etude de la capacite complexante des eaux de l'estuaire et de la baie de seine.

Analyses for the metals Cd, Pd and Cu in the estuary and bay of the Scine have been made. The site was chosen because of the very high tides, which produce considerable water displacement. For the purpose of analysis the metals have been divided into three categories: free metals, metals forming complexes that are unstable at low pH, and metals forming stable complexes that are destroyed in an acidic medium by ultraviolet radiation. The special properties of copper have been used to establish a "complexing capacity" of the different water samples studied. By making the simple hypothesis of the existence of an equilibrium of the type Cu + L right harpoon over left harpoon CuL, where L represents the ligand, the total ligand concentration, as well as the stability constants of the CuL complexes, has been determined. These results are presented and discussed.

[Not Available]. / Comportement electrochimique des thiocyanosulfates.

In a systematic study of the sulphonating properties of SO(3)B complexes, we have paid attention to the thiocyanosulphates KSO(3)SCN and NH(4)SO(3)SCN. We have shown conductimetrically that these salts are dissociated and that the ionic salvation is weak in the chosen solvent-sulpholane-which is strongly aprotic in character. We have determined potentiometrically the equilibrium constant K of the reaction MSO(3)SCN measured angle MSCN + SO(3), by means of the electrochemical couple Ag + SO(3)SCN(-) measured angle AgSCN + SO(3) + e(-). The values foun the ammonium and potassium salts are K = 10(-11.5 +/- 0.45) and 10(-9.7 +/- 0.7) respectively. Thiocyanosulphates appear to be stronger than chlorosulphates as sulphonating agents. Therefore SCN(-) is a weaker base than Cl(-) in sulpholane medium.

[Not Available]. / Etude electrochimique des sels de nitryle en milieu aprotonique.

The electrochemical reduction of NO(2)ClO(4) solutions at a platinum electrode in sulpholane has been studied. The results suggest the following scheme for the reduction of NO(+)(2) : 2NO(+)(2) + 2e(-) <==> 2NO(2) <==> N(2)O(4). A fast dimerization of nitrogen dioxide, which is favoured by the high donor number of sulpholane, follows the charge-transfer step. The NO(+)(2) ion is much more oxidative than the NO(+) ion in sulpholane, whereas the oxidizing power of the two species is nearly the same in nitromethane or acetonitrile solution. This result can be used to explain the role of water present at trace level.