International audience | Microbial communities driving the nitrogen cycle contribute to ecosystem services such as crop production and air, soil, and water quality. The responses to herbicide stress of ammonia-oxidizing and ammonia-denitrifying microbial communities were investigated by an analysis of changes in structure-function relationships. Their potential activities, abundances (quantitative PCR), and genetic structure (denaturing gradient gel electrophoresis) were assessed in a microcosm experiment. The application rate (1 × FR, 0.45 μg g(-1) soil) of the mesotrione herbicide did not strongly affect soil N-nutrient dynamics or microbial community structure and abundances. Doses of the commercial product Callisto® (10 × FR and 100 × FR) or pure mesotrione (100 × FR) exceeding field rates induced short-term inhibition of nitrification and a lasting stimulation of denitrification. These effects could play a part in the increase in soil ammonium content and decrease in nitrate contents observed in treated soils. These functional impacts were mainly correlated with abundance shifts of ammonia-oxidizing Bacteria (AOB) and Archaea (AOA) or denitrifying bacteria. The sustained restoration of nitrification activity, from day 42 in the 100 × FR-treated soils, was likely promoted by changes in the community size and composition of AOB, which suggests a leading role, rather than AOA, for soil nitrification restoration after herbicide stress. This ecotoxicological community approach provides a nonesuch multiparameter assessment of responses of N-cycling microbial guilds to pesticide stress.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA | International audience | This special issue of ESPR is focused on microbial ecotoxicology. What is ‘microbial ecotoxicology'? It is a branch of science that studies both (i) the ecological impacts of chemical (synthetic or natural origin) or biological (toxic species) pollution at the microbial scale and on the various functions that they ensure in the ecosystems and (ii) the role of microbial communities in the ecodynamic of the pollutants (source, transfer, degradation, transformation). It is a multidisciplinary scientific endeavor at the crossroad between microbial ecology, microbial toxicology, physics and chemistry (Fig. 1). It responds to an increasing demand worldwide of the politics and society because of the threat on environmental and human health caused by intense anthropogenic activities. In the context of the Anthropocene, microbial ecotoxicology seeks not only to conduct fundamental researches to understand the impact of pollutants on microbial processes and vice versa but also to carry out applied researches to provide tools readily usable by the society to monitor the evolution of the quality of the environment and to restore polluted sites.

International audience | The insecticide chlordecone applied for decades in banana plantations currently contaminates 20,000 ha of arable land in the French West Indies. Although the impact of various pesticides on soil microorganisms has been studied, chlordecone toxicity to the soil microbial community has never been assessed. We investigated in two different soils (sandy loam and silty loam) exposed to different concentrations of CLD (D0, control; D1 and D10, 1 and 10 times the agronomical dose) over different periods of time (3, 7, and 32 days): (i) the fate of chlordecone by measuring C-14-chlordecone mass balance and (ii) the impact of chlordecone on microbial community structure, abundance, and function, using standardized methods (-A-RISA, taxon-specific quantitative PCR (qPCR), and C-14-compounds mineralizing activity). Mineralization of C-14-chlordecone was inferior below 1 % of initial C-14-activity. Less than 2 % of C-14-activity was retrieved from the water-soluble fraction, while most of it remained in the organic-solvent-extractable fraction (75 % of initial C-14-activity). Only 23 % of the remaining C-14-activity was measured in nonextractable fraction. The fate of chlordecone significantly differed between the two soils. The soluble and nonextractable fractions were significantly higher in sandy loam soil than in silty loam soil. All the measured microbiological parameters allowed discriminating statistically the two soils and showed a variation over time. The genetic structure of the bacterial community remained insensitive to chlordecone exposure in silty loam soil. In response to chlordecone exposure, the abundance of Gram-negative bacterial groups (beta-, gamma-Proteobacteria, Planctomycetes, and Bacteroidetes) was significantly modified only in sandy loam soil. The mineralization of C-14-sodium acetate and C-14-2,4-d was insensitive to chlordecone exposure in silty loam soil. However, mineralization of C-14-sodium acetate was significantly reduced in soil microcosms of sandy loam soil exposed to chlordecone as compared to the control (D0). These data show that chlordecone exposure induced changes in microbial community taxonomic composition and function in one of the two soils, suggesting microbial toxicity of this organochlorine.

International audience

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED | International audience | Areas similar to free water surface constructed wetlands (FWS CWs) placed between wastewater treatment plants and receiving water bodies, under the perception that they increase water quality. More than 500 systems are in operation with a multitude of configurations and intended outcomes. In order to monitor these areas, research is being carried out to understand the fate of water and conventional pollutants in these systems. To this aim, a FWS CW located in southern France is monitored with traditional grab samples and 24-h flow composite samples. This site has also been instrumented with 6 Ion-Selective Electrodes (ISEs) probes recording continuously ammonium and nitrate concentrations. Because pollutant concentrations are usually low in treated wastewater, sometimes close to quantification limits of laboratory methods, we are developing appropriate methodologies for the management of the probes and the data processing. In this context, we propose a reliable methodology to increase the quality of data from ISE probes. This methodology is based on (i) laboratory experiments for sensor characterization and (ii) field tests. Laboratory experiments allowed characterizing the operating parameters like response time, linearity range, quantification limits, and interferences. Furthermore, for one-year, field tests are led every two weeks to (i) evaluate the required cleaning frequency and (ii) do grab samples analyses that help to validate data from the 6 ISEs. A drift in time appears to be significant for ammonium sensor. An additional experiment is currently monitoring this drift to correct this effect on measurement. This study has confirmed that it is fundamental to understand the technical limitations of the measuring equipment and set appropriate maintenance and calibration methodologies in order to have an accurate interpretation of data. The result is an operating protocol mainly concerning an acceptable cleaning frequency of two weeks, a stronger complementary calibration method using water from the experimental site, an evaluation of the drift and the determination of quantification limits of these ISEs (1 mg/L for ammonium and 0.5 m/L for nitrate). This protocol generates validated data that can be used to study nitrate and ammonium dynamics. In combination with the usual 24-h composite sampling method, it gives a good understanding of the fate of nitrogen within this FWS CW system. An example of data processing will be submitted.

International audience | Environmental controls of 2-methyl-4-chlorophenoxyacetic acid (MCPA) degradation are poorly understood. We investigated whether microbial MCPA degraders are stimulated by (maize) litter and whether this process depends on concentrations of MCPA and litter. In a microcosm experiment, different amounts of litter (0, 10 and 20 g kg(-1)) were added to soils exposed to three levels of the herbicide (0, 5 and 30 mg kg(-1)). The treated soils were incubated at 20 A degrees C for 6 weeks, and samples were taken after 1, 3 and 6 weeks of incubation. In soils with 5 mg kg(-1) MCPA, about 50 % of the MCPA was dissipated within 1 week of the incubation. Almost complete dissipation of the herbicide had occurred by the end of the incubation with no differences between the three litter amendments. At the higher concentration (30 mg kg(-1)), MCPA endured longer in the soil, with only 31 % of the initial amount being removed at the end of the experiment in the absence of litter. Litter addition greatly increased the dissipation rate with 70 and 80 % of the herbicide being dissipated in the 10 and 20 g kg(-1) litter treatments, respectively. Signs of toxic effects of MCPA on soil bacteria were observed from related phospholipid fatty acid (PLFA) analyses, while fungi showed higher tolerance to the increased MCPA levels. The abundance of bacterial tfdA genes in soil increased with the co-occurrence of litter and high MCPA concentration, indicating the importance of substrate availability in fostering MCPA-degrading bacteria and thereby improving the potential for removal of MCPA in the environment.

International audience | Nitrogen (N) fertilizer is an important yield limiting factor for sunflower production. The correlation between yield components and growth parameters of three sunflower hybrids (Hysun-33, Hysun-38, Pioneer-64A93) were studied with five N rates (0, 60, 120, 180, 240 kg ha−1) at three different experimental sites during the two consecutive growing seasons 2008 and 2009. The results revealed that total dry matter (TDM) production and grain yield were positively and linearly associated with leaf area index (LAI), leaf area duration (LAD), and crop growth rate (CGR) at all three sites of the experiments. The significant association of yield with growth components indicated that the humid climate was most suitable for sunflower production. Furthermore, the association of these components can be successfully used to predict the grain yield under diverse climatic conditions. The application of N at increased rate of 180 kg ha−1 resulted in maximum yield as compared to standard rate (120 kg ha−1) at all the experimental sites. In this way, N application rate was significantly correlated with growth and development of sunflower under a variety of climatic conditions. Keeping in view such relationship, the N dose can be optimized for sunflower crop in a particular region to maximize the productivity. Multilocation trails help to predict the input rates precisely while taking climatic variations into account also. In the long run, results of this study provides basis for sustainable sunflower production under changing climate.

International audience | In a globalized world, the world trade fleet plays a pivotal role in limiting transport costs. But, the management of obsolete ships is an acute problem, with most Ship Recycling Facilities (SRF) situated in developing countries. They are renowned for their controversial work and safety conditions and their environmental impact. Paradoxically, dismantlement is paid for by the shipowners in accordance with international conventions therefore it is more profitable for them to sell off ships destined for scrapping. Scuttling, the alternative to scrapping, is assessed in the present review to compare the cost/benefit ratios of the two approaches. Although scrapping provides employment and raw materials – but with environmental, health and safety costs – scuttling provides fisheries and diving tourism opportunities but needs appropriate management to avoid organic and metal pollution, introduction of invasive species and exacerbation of coastal erosion. It is also limited by appropriate bottom depth, ship type and number. The present review inventories the environmental, health, safety, economic, and forensic aspects of each alternative.