International audience | The desorption rate is an important factor determining cadmium (Cd) ecotoxicity and pollution remediation in soils. The pedotransfer functions (PTFs) of desorption rate coefficients of fresh Cd in soils have been developed in literature. We hypothesized that the aging of Cd pollution would alter Cd desorption process. Taking historically polluted soils as the object, this study aimed at testing the hypothesis and developing new PTFs of desorption rate coefficients for historical Cd. 15 d batch extraction experiments and 13 kinetic models were employed to define Cd desorption rate coefficients in 27 historically polluted soil samples. Compared with fresh Cd, the desorption rate coefficients of historical Cd were lower, and the break time of biphasic desorption processes was retarded to 3 d (4320 min). Different with the usual models for fresh Cd desorption (e.g. parabolic diffusion and two constant rate models), the best models to mimic the historical Cd desorption processes were the pseudo first order, logarithmic, Elovich, and simple Elovich models. The rate-limiting step controlling Cd desorption was changed from the intraparticle diffusion to the interface reaction with aging of pollution. New PTFs of desorption rate coefficients of historical Cd were established (R2 ≥ 0.71). Cd desorption rate coefficients increased with organic matter and clay contents, but decreased with oxalate extractable Fe content, solution pH, cation exchange capacity, and silt content. The key soil properties influencing desorption rate coefficients were not altered by the aging of pollution. The developed PTFs could guide us to adjusting the ecotoxicity and pollution remediation of Cd in historically polluted field soils.

International audience | Macrophytes are known to bioaccumulate metals, but a thorough understanding of tolerance strategies and molecular impact of metals in aquatic plants is still lacking. The present study aimed to compare Hg and Cd effects in a representative macrophyte, Elodea nuttallii using physiological endpoints and metabolite profiles in shoots and cytosol. Exposure 24 h to methyl-Hg (30 ng L), inorganic Hg (70 ng L) and Cd (280 μg L) did not affect photosynthesis, or antioxidant enzymes despite the significant accumulation of metals, confirming a sublethal stress level. In shoots, Cd resulted in a higher level of regulation of metabolites than MeHg, while MeHg resulted in the largest number of regulated metabolites and IHg treatment regulated no metabolites significantly. In cytosol, Cd regulated more metabolites than IHg and only arginine, histidine and mannose were reduced by MeHg exposure. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of data suggested that exposure to MeHg resulted in biochemical changes including aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism, nitrogen metabolism, arginine and proline metabolism, cyanoamino acid metabolism, while the treatment of Cd stress caused significant variations in aminoacyl-tRNA biosynthesis and branched-chain amino acids pathways. Data supports an impact of MeHg on N homeostasis, while Cd resulted in an osmotic stress-like pattern and IHg had a low impact. Marked differences in the responses to MeHg and IHg exposure were evidenced, supporting different molecular toxicity pathways and main impact of MeHg on non-soluble compartment, while main impact of IHg was on soluble compartment. Metabolomics was used for the first time in this species and proved to be very useful to confirm and complement recent knowledge gained by transcriptomics and proteomics, highlighting the high interest of multi-omics approaches to identify early impact of environmental pollution.

The impact of ozone (O3) pollution events on the plant drought response needs special attention because spring O3 episodes are often followed by summer drought. By causing stomatal sluggishness, O3 could affect the stomatal dynamic during a subsequent drought event. In this context, we studied the impact of O3 exposure and water deficit (in the presence or in the absence of O3 episode) on the stomatal closure/opening mechanisms relative to irradiance or vapour pressure deficit (VPD) variation. Two genotypes of Populus nigra x deltoides were exposed to various treatments for 21 days. Saplings were exposed to 80 ppb/day O3 for 13 days, and then to moderate drought for 7 days. The curves of the stomatal response to irradiance and VPD changes were determined after 13 days of O3 exposure, and after 21 days in the case of subsequent water deficit, and then fitted using a sigmoidal model. The main responses under O3 exposure were stomatal closure and sluggishness, but the two genotypes showed contrasting responses. During stomatal closure induced by a change in irradiance, closure was slower for both genotypes. Nonetheless, the genotypes differed in stomatal opening under light. Carpaccio stomata opened more slowly than control stomata, whereas Robusta stomata tended to open faster. These effects could be of particular interest, as stomatal impairment was still present after O3 exposure and could result from imperfect recovery. Under water deficit alone, we observed slower stomatal closure in response to VPD and irradiance, but faster stomatal opening in response to irradiance, more marked in Carpaccio. Under the combined treatment, most of the parameters showed antagonistic responses. Our results highlight that it is important to take genotype-specific responses and interactive stress cross-talk into account to improve the prediction of stomatal conductance in response to various environmental modifications.

The impact of ozone (O3) pollution events on the plant drought response needs special attention because spring O3 episodes are often followed by summer drought. By causing stomatal sluggishness, O3 could affect the stomatal dynamic during a subsequent drought event. In this context, we studied the impact of O3 exposure and water deficit (in the presence or in the absence of O3 episode) on the stomatal closure/opening mechanisms relative to irradiance or vapour pressure deficit (VPD) variation. Two genotypes of Populus nigra x deltoides were exposed to various treatments for 21 days. Saplings were exposed to 80 ppb/day O3 for 13 days, and then to moderate drought for 7 days. The curves of the stomatal response to irradiance and VPD changes were determined after 13 days of O3 exposure, and after 21 days in the case of subsequent water deficit, and then fitted using a sigmoidal model. The main responses under O3 exposure were stomatal closure and sluggishness, but the two genotypes showed contrasting responses. During stomatal closure induced by a change in irradiance, closure was slower for both genotypes. Nonetheless, the genotypes differed in stomatal opening under light. Carpaccio stomata opened more slowly than control stomata, whereas Robusta stomata tended to open faster. These effects could be of particular interest, as stomatal impairment was still present after O3 exposure and could result from imperfect recovery. Under water deficit alone, we observed slower stomatal closure in response to VPD and irradiance, but faster stomatal opening in response to irradiance, more marked in Carpaccio. Under the combined treatment, most of the parameters showed antagonistic responses. Our results highlight that it is important to take genotype-specific responses and interactive stress cross-talk into account to improve the prediction of stomatal conductance in response to various environmental modifications.

International audience | Environmental contamination is one of the major factors or cofactors affecting amphibian populations. Since 2000, the number of studies conducted in laboratory conditions to understand impacts of chemical exposures increased. They aimed to characterize biological effects on amphibians. This review proposes an overview of biological responses reported after exposures to metals, phytopharmaceuticals or emerging organic contaminants and focuses on endpoints relating to reproduction and development. Due to amphibian peculiar features, these periods of their life cycle are especially critical to pollutant exposures. Despite the large range of tested compounds, the same model species are often used as biological models and morphological alterations are the most studied observations. From the results, the laboratory-to-field extrapolation remained uneasy and exposure designs have to be more elaborated to be closer to environmental conditions. Few studies proposed such experimental approaches. Lastly, gametes, embryos and larvae constitute key stages of amphibian life cycle that can be harmed by exposures to freshwater pollutants. Specific efforts have to be intensified on the earliest stages and notably germ cells.

Soil contamination due to atmospheric deposition of metals originating from smelters is a global environmental problem. A common problem associated with this contamination is the discrimination between anthropic and natural contributions to soil metal concentrations: In this context, we investigated the characteristics of soil contamination in the surrounding area of a world class smelter. We attempted to combine several approaches in order to identify sources of metals in soils and to examine contamination characteristics, such as pollution level, range, and spatial distribution. Soil samples were collected at 100 sites during a field survey and total concentrations of As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, and Zn were analyzed. We conducted a multivariate statistical analysis, and also examined the spatial distribution by 1) identifying the horizontal variation of metals according to particular wind directions and distance from the smelter and 2) drawing a distribution map by means of a GIS tool. As, Cd, Cu, Hg, Pb, and Zn in the soil were found to originate from smelter emissions, and As also originated from other sources such as abandoned mines and waste landfill. Among anthropogenic metals, the horizontal distribution of Cd, Hg, Pb, and Zn according to the downwind direction and distance from the smelter showed a typical feature of atmospheric deposition (regression model: y = y0 + αe−βx). Lithogenic Fe was used as an indicator, and it revealed the continuous input and accumulation of these four elements in the surrounding soils. Our approach was effective in clearly identifying the sources of metals and analyzing their contamination characteristics. We believe this study will provide useful information to future studies on soil pollution by metals around smelters.

International audience | Microplastics (<5 mm) exhibit intrinsic features such as density, hydrophobic surface, or high surface/volume ratio, that are known to promote microbial colonization and biofilm formation in marine ecosystems. Yet, a relatively low number of studies have investigated the nature of microplastic associated bacterial communities in coastal ecosystems and the potential factors influencing their composition and structure. Here, we characterized microplastics collected in the Bay of Brest by manual sorting followed by Raman spectroscopy and studied their associated bacterial assemblages using 16S amplicon high-throughput sequencing. Our methodology allowed discriminating polymer type (polyethylene, polypropylene and polystyrene) within small size ranges (0.3-1 vs. 1-2 vs. 2-5 mm) of microplastics collected. Data showed high species richness and diversity on microplastics compared to surrounding seawater samples encompassing both free living and particle attached bacteria. Even though a high proportion of operational taxonomic units (OTU; 94 ± 4%) was shared among all plastic polymers, polystyrene fragments exhibited distinct bacterial assemblages as compared to polyethylene and polypropylene samples. No effect of microplastic size was revealed regardless of polymer type, site and date of collection. The Vibrio genus was commonly detected in the microplastic fraction and specific PCR were performed to determine the presence of potentially pathogenic Vibrio strains (namely V. aestuarianus and the V. splendidus polyphyletic group). V. splendidus related species harboring

International audience | With the large amount of attention being given to microplastics in the environment, several researchers have begun to consider the fragmentation of plastics down to lower scales (i.e., the sub-micrometer scale). The term “nanoplastics” is still under debate, and different studies have set the upper size limit at either 1000 nm or 100 nm. The aim of the present work is to propose a definition of nanoplastics, based on our recently published and unpublished research definition of nanoplastics. We define nanoplastics as particles unintentionally produced (i.e. from the degradation and the manufacturing of the plastic objects) and presenting a colloidal behavior, within the size range from 1 to 1000 nm.