Validation of a multilevel sampling device to determine the vertical variability of chlorinated solvent in a contaminated aquifer.

The vertical heterogeneity of contaminant concentrations in aquifers is well known, but obtaining representative samples is still a subject of debate. In this paper, the question arises from sites where numerous fully screened wells exist and there is a need to define the vertical distribution of contaminants. For this purpose, several wells were investigated with different techniques on a site contaminated with chlorinated solvents. A core-bored well shows that a tetrachloroethene (PCE) phase is sitting on and infiltrating a less permeable layer. Downstream of the cored well, the following sampling techniques were compared on fully screened wells: low flow pumping at several depths, pumping between packers and a new multilevel sampler for fully screened wells. Concerning low flow rate pumping, very low gradients were found, which may be due to the existence of vertical flow inside the well or in the gravel pack. Sampling between packers gave results comparable with the cores, separating a layer with PCE and trichloroethene from another one with cis 1,2-dichloroethene and vinyl chloride as major compounds. Detailed sampling according to pumped volume shows that even between packers, cleaning of the inter-packer volume is necessary before each sampling. Lastly, the proposed new multilevel sampler gives results similar to the packers but has the advantages of much faster sampling and a constant vertical positioning, which is fairly important for long-term monitoring in highly stratified aquifers.

In situ assessment of phytotechnologies for multicontaminated soil management.

Due to human activities, large volumes of soils are contaminated with organic pollutants such as polycyclic aromatic hydrocarbons, and very often by metallic pollutants as well. Multipolluted soils are therefore a key concern for remediation. This work presents a long-term evaluation of the fate and environmental impact of the organic and metallic contaminants of an industrially polluted soil under natural and plant-assisted conditions. A field trial was followed for four years according to six treatments in four replicates: unplanted, planted with alfalfa with or without mycorrhizal inoculation, planted with Noccaea caerulescens, naturally colonized by indigenous plants, and thermally treated soil planted with alfalfa. Leaching water volumes and composition, PAH concentrations in soil and solutions, soil fauna and microbial diversity, soil and solution toxicity using standardized bioassays, plant biomass, mycorrhizal colonization, were monitored. Results showed that plant cover alone did not affect total contaminant concentrations in soil. However, it was most efficient in improving the contamination impact on the environment and in increasing the biological diversity. Leaching water quality remained an issue because of its high toxicity shown by micro-algae testing. In this matter, prior treatment of the soil by thermal desorption proved to be the only effective treatment.

A new strategy useful for rapid identification of microsatellites from DNA libraries with large size inserts.

Microsatellites are new powerful polymorphic markers used for gene mapping. Their characterization requires that all the sequence surrounding the repeat be known in order to be able to design primers for PCR amplification. However, when using DNA libraries with large cloned inserts, this sequence characterization is not immediately practicable. In this paper, we describe a new strategy, based both on the use of a microsatellite specific probing and on the creation of nested deleted clones with the Exonuclease III, in order to position microsatellites in a range allowing direct sequencing. This method was applied to the screening of a mouse chromosome 19 DNA specific library. In this way, thirteen clones were identified by specific probing and seven were submitted to the nested deletion strategy. Five of them presented microsatellite sequences in specific deleted subclones which were selected and sequenced. Primers were designed for each of them and polymorphism between the genomes of several inbred strain of mouse have been determined. These microsatellites were mapped, three of them to chromosome 19 and two to chromosome 11.