Impact des traitement de potabilisation sur le CODB et la distribution des substances humiques et non humiques de la matière organique naturelle

Cette étude a consisté à évaluer et à comparer l'impact des traitements de coagulation-floculation, ozonation et filtration sur charbon actif en grains sur la matière organique dissoute de différentes eaux de rivières et de retenues françaises en s'appuyant sur le suivi de deux paramètres principaux, la fraction biodégradable du carbone organique dissous (CODB) et la distribution des substances humiques et non humiques (établie sur la base d'un protocole de filtration en série sur résines XAD-8 et XAD-4 ).Dans le cas des eaux étudiées, la coagulation-floculation s'est accompagnée d'une diminution importante du COD, soit 38 à 70 %, impact qui se répercute dans des proportions équivalentes au niveau de sa fraction biodégradable soit 38 à 88%. Dans la majorité des cas, la clarification conduit à l'élimination préférentielle des substances humiques (définies comme hydrophobes), qui correspondent aux fractions de plus hautes masses moléculaires. Comparativement, et pour des taux supérieurs à 1 mg O3/mg C, l'ozonation entra"ne une réduction de la fraction des substances humiques qui se traduit par une augmentation de la fraction des substances non humiques et en particulier des substances hydrophiles non adsorbées sur résines XAD-8 et XAD-4. Cette modification, d'autant plus marquée que le taux d'ozone est important, s'accompagne d'une augmentation proportionnelle de la fraction biodégradable du COD. Le suivi en usine a montré que les taux d'ozone appliqués lors d'une interozonation modifient peu la nature du COD. Par contre, la filtration sur charbon actif en aval change de manière importante la distribution de la matière organique dissoute avec une augmentation relative de la fraction hydrophobe et des composés de faibles masses moléculaires apparentes (< 1 000 daltons).The goal of our study was to evaluate the impact of water treatment processes (i.e. coagulation- flocculation, ozonation and GAC filtration) on the natural organic matter (NOM) of various river and reservoir waters based on DOC and BDOC analyses and the determination of the humic/non humic NOM distribution (fractionation of the DOC at acidic pH using two successive XAD-8 and XAD-4 resin columns). Analyses carried out on ten French raw surface waters have shown that the BDOC fraction accounted for 11 to 38 % of the DOC. The humic/non humic distribution of the NOM varied slightly with the origin of the studied water. About 50 to 60 % of the DOC was found to be incorporated into the humic fraction (NOM adsorbed on the XAD-8 resin), the hydrophilic acids (adsorbed on the XAD-4 resin) accounted for 10 to 25 % of the DOC while the non adsorbed hydrophilic solutes (hydrophilic neutrals that constitute the XAD-8/XAD-4 effluent) represented 15 to 30 % of the DOC.Clarified water samples were collected from water treatment plants after coagulation/flocculation/sand filtration when no preoxidation was used. For water utilities which included a preoxidation step in their treatment process, raw water samples were coagulated and flocculated at a laboratory scale with Jar Test equipment using the same conditions (nature of the coagulant, pH, dose) as those used in the corresponding treatment plant. Globally, 38 to 70 % of the DOC and 38 to 88 % of the BDOC were removed during coagulation-flocculation, depending on the water site. In general, the humic/non humic NOM distribution of clarified waters showed a slight increase in the proportion of the non humic organic fraction as compared to raw waters, which indicates that humic substances (higher molecular weight organics) are preferentially removed during coagulation-flocculation. Ozonation experiments were carried out on a raw water and a clarified water sampled from the same water site using a semi batch reactor (ozone was generated from high purity oxygen). For both waters, very little variation of the humic/non humic NOM distribution was observed for applied ozone doses around 0.5 mg O3/mg C or below. For higher ozone doses, the NOM distribution was dramatically changed despite only a small reduction of the DOC. The large reduction of the humic fraction was followed by a proportional increase of the non adsorbed hydrophilic solute fraction (small reduction of the DOC). As the applied ozone dose was increased from 1 to 3 mg O3/mg DOC, the non-adsorbed hydrophilic solute fraction also increased. The shift from high molecular weight organics such as humic materials to more hydrophilic organics (high polarity and low molecular weight organic solutes) during ozonation has often been mentioned in the literature. The increase of the non humic substances was followed by an increase of the BDOC. Results have also shown that higher ozone doses yield higher BDOC. Similar observations could be made with the raw and the clarified water.As a conclusion of this work, samples were collected at the different steps of a water treatment plant (raw water, clarified water, intermediate ozonated water, GAC filtered water). The impact of coagulation/flocculation, and intermediate ozonation on BDOC and the humic/non humic NOM distribution confirmed the previous observations. The GAC filtration had a large impact on the DOC distribution while the BDOC was only slightly reduced. The NOM of the treated water was found to be more hydrophobic in nature with compounds that showed apparent molecular weights below 1 000 daltons (more than 80 % of the DOC)

2′-Chloro-4-meth­oxy-3-nitro­benzil

In the title compound, C15H10ClNO5, the dihedral angle between the aromatic rings is 87.99 (5)°. The O—C—C—O torsion angle between the two carbonyl units is −119.03 (16)°. The crystal structure is stabilized by a weak intermolecular C—H⋯O hydrogen bond

An efficient method to find potentially universal population genetic markers, applied to metazoans

<p>Abstract</p> <p>Background</p> <p>Despite the impressive growth of sequence databases, the limited availability of nuclear markers that are sufficiently polymorphic for population genetics and phylogeography and applicable across various phyla restricts many potential studies, particularly in non-model organisms. Numerous introns have invariant positions among kingdoms, providing a potential source for such markers. Unfortunately, most of the few known EPIC (Exon Primed Intron Crossing) loci are restricted to vertebrates or belong to multigenic families.</p> <p>Results</p> <p>In order to develop markers with broad applicability, we designed a bioinformatic approach aimed at avoiding multigenic families while identifying intron positions conserved across metazoan phyla. We developed a program facilitating the identification of EPIC loci which allowed slight variation in intron position. From the <it>Homolens </it>databases we selected 29 gene families which contained 52 promising introns for which we designed 93 primer pairs. PCR tests were performed on several ascidians, echinoderms, bivalves and cnidarians. On average, 24 different introns per genus were amplified in bilaterians. Remarkably, five of the introns successfully amplified in all of the metazoan genera tested (a dozen genera, including cnidarians). The influence of several factors on amplification success was investigated. Success rate was not related to the phylogenetic relatedness of a taxon to the groups that most influenced primer design, showing that these EPIC markers are extremely conserved in animals.</p> <p>Conclusions</p> <p>Our new method now makes it possible to (i) rapidly isolate a set of EPIC markers for any phylum, even outside the animal kingdom, and thus, (ii) compare genetic diversity at potentially homologous polymorphic loci between divergent taxa.</p

Evolutionary stasis of the pseudoautosomal boundary in strepsirrhine primates

Sex chromosomes are typically comprised of a non-recombining region and a recombining pseudoautosomal region. Accurately quantifying the relative size of these regions is critical for sex-chromosome biology both from a functional and evolutionary perspective. The evolution of the pseudoautosomal boundary (PAB) is well documented in haplorrhines (apes and monkeys) but not in strepsirrhines (lemurs and lorises). Here, we studied the PAB of seven species representing the main strepsirrhine lineages by sequencing a male and a female genome in each species and using sex differences in coverage to identify the PAB. We found that during primate evolution, the PAB has remained unchanged in strepsirrhines whereas several recombination suppression events moved the PAB and shortened the pseudoautosomal region in haplorrhines. Strepsirrhines are well known to have much lower sexual dimorphism than haplorrhines. We suggest that mutations with antagonistic effects between males and females have driven recombination suppression and PAB evolution in haplorrhines

Identifying frequency decorrelated dust residuals in B-mode maps by exploiting the spectral capability of bolometric interferometry

Astrophysical polarized foregrounds represent the most critical challenge in Cosmic Microwave Background (CMB) B-mode experiments. Multi-frequency observations can be used to constrain astrophysical foregrounds to isolate the CMB contribution. However, recent observations indicate that foreground emission may be more complex than anticipated. We investigate how the increased spectral resolution provided by band splitting in Bolometric Interferometry (BI) through a technique called spectral imaging can help control the foreground contamination in the case of unaccounted Galactic dust frequency decorrelation along the line-of-sight. We focus on the next generation ground-based CMB experiment CMB-S4, and compare its anticipated sensitivities, frequency and sky coverage with a hypothetical version of the same experiment based on BI. We perform a Monte-Carlo analysis based on parametric component separation methods (FGBuster and Commander) and compute the likelihood on the recovered tensor-to-scalar ratio. The main result of this analysis is that spectral imaging allows us to detect systematic uncertainties on r from frequency decorrelation when this effect is not accounted for in component separation. Conversely, an imager would detect a biased value of r and would be unable to spot the presence of a systematic effect. We find a similar result in the reconstruction of the dust spectral index, where we show that with BI we can measure more precisely the dust spectral index also when frequency decorrelation is present. The in-band frequency resolution provided by BI allows us to identify dust LOS frequency decorrelation residuals where an imager of similar performance would fail. This opens the prospect to exploit this potential in the context of future CMB polarization experiments that will be challenged by complex foregrounds in their quest for B-modes detection.Comment: 13 Pages, 15 figures, 4 tables. Submitted to A&

Rapid De Novo Evolution of X Chromosome Dosage Compensation in Silene latifolia, a Plant with Young Sex Chromosomes

Evidence for dosage compensation in Silene latifolia, a plant with 10-million-year-old sex chromosomes, reveals that dosage compensation can evolve rapidly in young XY systems and is not an animal-specific phenomenon

Population Genomic Inferences from Sparse High-Throughput Sequencing of Two Populations of Drosophila melanogaster

Short-read sequencing techniques provide the opportunity to capture genome-wide sequence data in a single experiment. A current challenge is to identify questions that shallow-depth genomic data can address successfully and to develop corresponding analytical methods that are statistically sound. Here, we apply the Roche/454 platform to survey natural variation in strains of Drosophila melanogaster from an African (n = 3) and a North American (n = 6) population. Reads were aligned to the reference D. melanogaster genomic assembly, single nucleotide polymorphisms were identified, and nucleotide variation was quantified genome wide. Simulations and empirical results suggest that nucleotide diversity can be accurately estimated from sparse data with as little as 0.2× coverage per line. The unbiased genomic sampling provided by random short-read sequencing also allows insight into distributions of transposable elements and copy number polymorphisms found within populations and demonstrates that short-read sequencing methods provide an efficient means to quantify variation in genome organization and content. Continued development of methods for statistical inference of shallow-depth genome-wide sequencing data will allow such sparse, partial data sets to become the norm in the emerging field of population genomics

Fully Bayesian tests of neutrality using genealogical summary statistics

<p>Abstract</p> <p>Background</p> <p>Many data summary statistics have been developed to detect departures from neutral expectations of evolutionary models. However questions about the neutrality of the evolution of genetic loci within natural populations remain difficult to assess. One critical cause of this difficulty is that most methods for testing neutrality make simplifying assumptions simultaneously about the mutational model and the population size model. Consequentially, rejecting the null hypothesis of neutrality under these methods could result from violations of either or both assumptions, making interpretation troublesome.</p> <p>Results</p> <p>Here we harness posterior predictive simulation to exploit summary statistics of both the data and model parameters to test the goodness-of-fit of standard models of evolution. We apply the method to test the selective neutrality of molecular evolution in non-recombining gene genealogies and we demonstrate the utility of our method on four real data sets, identifying significant departures of neutrality in human influenza A virus, even after controlling for variation in population size.</p> <p>Conclusion</p> <p>Importantly, by employing a full model-based Bayesian analysis, our method separates the effects of demography from the effects of selection. The method also allows multiple summary statistics to be used in concert, thus potentially increasing sensitivity. Furthermore, our method remains useful in situations where analytical expectations and variances of summary statistics are not available. This aspect has great potential for the analysis of temporally spaced data, an expanding area previously ignored for limited availability of theory and methods.</p