A dynamic leaching method for the assessment of trace metals released from hydraulic binders.

With respect to sustainable development, the leachability of trace metal from solid materials in contact with water has focused much attention over the years. Portland cements produced in industrial kilns generally contain from 10 to 300 mg/kg of trace metals. The behaviour of these endogenous metals has been, in this regard, the target of different leaching studies. Many of these researches concluded that heavy metals release are lower than analytical detection limits. Although satisfying from an environmental point of view, it induces a lack in the knowledge about the trace metals behavior during the leaching of cement based material. Accordingly, we designed the CTG-LEACHCRETE device, a dynamic leaching system (modified Soxhlet type) that overcomes this difficulty and allows long term monitoring. The experimental procedure is presented and preliminary results are discussed.

Heavy metal contamination of settling particles in a retention pond along the A-71 motorway in Sologne, France.

A retention pond is a part of a drainage system designed to control water flow during rainstorms and to trap contaminated solid particles washed off by runoff water from a motorway. A series of studies have been carried out concerning the physico-chemical characteristics of the particles which settle down in such a pond in order to evaluate the effectiveness of the pond as a trap for heavy metals such as Pb, Zn and Cd. The highly contaminated roadside soil and the uncontaminated background soil were also studied for comparison. The settling particles had heavy metal concentrations 2-8 times higher than the background Sologne soil, depending on the metals. Heavy metal concentrations in the roadside soil were 7-26 times higher than those in the former. Sequential extractions, using the procedure of Tessier et al. (1979) illustrate that the highly contaminated roadside soil consisted mainly of the readily soluble fractions for all three heavy metals, with a limited proportion of residual metals. In the settling particles, the proportion of the latter is significantly increased, up to one-third of the total. The high concentration differences between the roadside soil and the settling particles indicates that most of the heavy metals are lost to the surroundings even before reaching the retention pond. Cadmium exhibited a specific behavior in that the most soluble fraction (exchangeable), which is negligible for Pb and Zn, occupied as much as one-fourth of the total in the roadside soil. Based on the 'enrichment factor' normalized to Fe introduced by Helz in 1976, the degree of contamination by heavy metals for the roadside soil and the settling particles was evaluated. The level of contamination was very severe in the roadside soil, while it was not so great in the settling particles. Suggestions are made to improve their removal efficiency.

In vitro assessment of the biopersistence of vitreous fibers: state of the art from the physical-chemical point of view.

Biopersistence is a function of different parameters: low solubility of the vitreous phase in physiological media, good mechanical properties of altered fibers, limited ability of phagocytosis to digest residual fragments. This article emphasizes solubility problems. From studies related to nuclear waste storage and other industrial problems, the mechanisms (formation of a leached layer of variable thickness and structure) and the kinetic laws describing the dissolution of vitreous fibers are now fairly well known. Appropriate methods depend only on the composition of the vitreous fibers that have to be chosen to determine intrinsic dissolution rates. All other parameters influencing the dissolution rate have to be fixed radius of the fibers, composition of the saline solution) or within a convenient range (flow-rate, s/v ratio). Alternatively, physicochemical parameters may be derived from a known relation (Arrhenius plot for T, kinetic equation for pH, geometrical equation for S). In spite of their widespread use, flow-through systems, in our opinion, give less precise kinetic results than large-volume closed systems with small s/v ratios (less than 0.5 cm-1). In closed and open systems, we suggest the use of two parameters for describing the dissolution rates at 37 degrees C: the initial rate constant, vo, and the time constant, k, for a rate decreasing at variable S.

Chemical behavior of aluminum and phosphorus during dissolution of glass fibers in physiological saline solutions.

The dissolution of textile glass fibers of four different compositions has been investigated at 37 degrees C. In these glasses, which are isolation type, the P2O5 contents scatter between 0 and 2 wt% and Al2O3 from 0.12 to 3.4 wt%. Both static (30-mg fibers; 250-ml solution) and dynamic (50-mg fibers; 40 ml/day flow rate) conditions with or without bubbling of a gas mixture (95:5, N2-CO2) have been used. Two physiological solutions, one proposed by Kanapilly and the other by Scholtze, were used. After each run (1, 3, 7, 14, and sometimes 30, 62 days) the solutions were analyzed for B and Si by inductively coupled plasma (ICP), the weight losses were determined, and the residual solid were observed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static runs give a better agreement between measured and calculated weight losses from solution analyses than dynamic experiments. SEM examinations indicate diameter reduction and formation of a hydrated Si-rich layer. Sometimes hollow tubes, suggesting the detachment of these layers, are observed. XPS and energy dispersive X-ray (EDX) analysis indicate the formation of a veneer of calcium phosphate for the most rapidly dissolving glass. In other cases an Al increase is observed at the solid solution interface. Whatever experimental conditions are used, the relative dissolution rates of the four glasses are identical. The kinetics may be modeled with variable dissolution rates from initial high values to final low ones. The latter reflect the very low solubility of the residual product.

[Comparative study, with photoelectron spectroscopy of the adsorption of phospholipids by 3 fibrous silicate minerals (chrysotile, crocidolite, attapulgite)]. / Etude comparative, par spectroscopie de photoélectrons de l'adsorption de phospholipides par trois minéraux silicatés fibreux (chrysotile, crocidolite, attapulgite).

The method used in this study for preparing mineral samples has allowed us to obtain a highly reproducible surface state, which in turn means that we can better exploit the results of the XPS analysis. With high initial concentrations, the three minerals studied appeared to be covered with a bilayer of phospholipids. The greatest adsorption was obtained with initial phospholipid concentrations of 100, 150 and 300 micrograms/ml for crocidolite, chrysotile and attapulgite respectively. It would appear that these differences in surface reactivity can be related to the different levels of risk associated with the inhalation of these fibres.

[Choriocarcinoma in mother and child (author's transl)]. / Métastases chez un nourrisson d'un choriocarcinome placentaire.

The case of a 2 month-old child with metastatic choriocarcinoma is reported. Death occurred rapidly and necropsy failed to find a primary tumor; the choriocarcinoma was therefore thought to be developed in the placenta. A year later, a uterine exploration was performed in the mother. In spite of normal chorionic gonadotrophin levels the histological findings were compatible with choriocarcinoma.

Chemical and photoelectron spectrometry analysis of the adsorption of phospholipid model membranes and red blood cell membranes on to chrysotile fibres.

A study of the interaction of phospholipid model membranes and red blood cell membranes with UICC A chrysotile fibres using chemical analysis and photoelectron spectrometry showed that the interaction agreed with an adsorption of the membranes on to the chrysotile fibres. The photoelectron spectrometry analysis allowed the statement that phospholipid model membranes are adsorbed as bilayer. Chemical analysis showed that for each milligram of chrysotile the amount of phospholipids adsorbed was about 155 microgram and the available surface for phospholipids was about 38 m/g. It was established that entire membranes were adsorbed. A mechanism for the haemolytic capacity of chrysotile is suggested.

Surface interaction between chrysotile and solutions (dissolution and adsorption): systematic x-ray photoelectron spectroscopy studies.

To test the reactivity of asbestos in relation to its physical and structural properties, surface analysis was made by X-ray photoelectron spectroscopy. The dissolution kinetics of chrysotile in strong reagents demonstrate two rate-limiting steps for the reaction: Mg2+ diffusion and chemical reaction. In some components of the Krebs cycle and in dilute hydrochloric and in oxalic acids, the reaction is limited by the exchange of Mg2+ in the first mineral layer. The interaction of model phospholipid membranes with chrysotile fibres was also studied; the results are in good agreement with the hypothesis of bilayer adsorption. Photoelectron data for adsorption of ghosts indicate that both proteins and phospholipids must be adsorbed onto chrysotile fibres.

[Adsorption of phospholipids by chrysotile fibers : comparison of data from chemical analysis and photoelectron spectrometry (PSX method)]. / Etude de l'adsorption des phospholipides par les fibres de chrysotile : confrontation des données de l'analyse chimique et de la spectrométrie de photoélectrons (méthode XPS).

The adsorption of dipalmitoyl phosphatidyl choline (DPPC) by chrysotile fibers was carried out by chemical and photoelectron spectroscopy analysis. The adsorption isotherms have shown that maximum adsorption was about 130 microgram of DPPC per milligram of chrysotile. The results are in good agreement with estimates of a bilayer adsorption.