Negative Effects of Copper Oxide Nanoparticles on Carbon and Nitrogen Cycle Microbial Activities in Contrasting Agricultural Soils and in Presence of Plants

Metal-oxide nanoparticles (NPs) such as copper oxide (CuO) NPs offer promising perspectives for the development of novel agro-chemical formulations of pesticides and fertilizers. However, their potential impact on agro-ecosystem functioning still remains to be investigated. Here, we assessed the impact of CuO-NPs (0.1, 1, and 100 mg/kg dry soil) on soil microbial activities involved in the carbon and nitrogen cycles in five contrasting agricultural soils in a microcosm experiment over 90 days. Additionally, in a pot experiment, we evaluated the influence of plant presence on the toxicity of CuO-NPs on soil microbial activities. CuO-NPs caused significant reductions of the three microbial activities measured (denitrification, nitrification, and soil respiration) at 100 mg/kg dry soil, but the low concentrations (0.1 and 1 mg/kg) had limited effects. We observed that denitrification was the most sensitive microbial activity to CuO-NPs in most soil types, while soil respiration and nitrification were mainly impacted in coarse soils with low organic matter content. Additionally, large decreases in heterotrophic microbial activities were observed in soils planted with wheat, even at 1 mg/kg for soil substrate-induced respiration, indicating that plant presence did not mitigate or compensate CuO-NP toxicity for microorganisms. These two experiments show that CuO-NPs can have detrimental effects on microbial activities in soils with contrasting physicochemical properties and previously exposed to various agricultural practices. Moreover, we observed that the negative effects of CuO-NPs increased over time, indicating that short-term studies (hours, days) may underestimate the risks posed by these contaminants in soils

Impact of engineered nanoparticles on the activity, abundance, and diversity of soil microbial communities: a review

This report presents an exhaustive literature review of the effects of engineered nanoparticles on soil microbial communities. The toxic effects on microbial communities are highly dependent on the type of nanoparticles considered. Inorganic nanoparticles (metal and metal oxide) seem to have a greater toxic potential than organic nanoparticles (fullerenes and carbon nanotubes) on soil microorganisms. Detrimental effects of metal and metal oxide nanoparticles on microbial activity, abundance, and diversity have been demonstrated, even for very low concentrations (250 mg kg(-1)), representing a worst case scenario. Considering that most of the available literature has analyzed the impact of an acute contamination of nanoparticles using high concentrations in a single soil, several research needs have been identified, and new directions have been proposed. The effects of realistic concentrations of nanoparticles based on the concentrations predicted in modelization studies and chronic contaminations should be simulated. The influence of soil properties on the nanoparticle toxicity is still unknown and that is why it is crucial to consider the ecotoxicity of nanoparticles in a range of different soils. The identification of soil parameters controlling the bioavailability and toxicity of nanoparticles is fundamental for a better environmental risk assessment

Biopurification of air containing a low concentration of TEX: comparison of removal efficiency using planted and non-planted biofilters

International audienceBACKGROUND: Underground car parks are confined spaces where traffic generates many pollutants such as toluene, ethylbenzene and xylene (TEX) and nitrogen oxides (NOx). The objective of this work was to evaluate the removal efficiency of low concentrations of TEX using planted and non-planted biofilters. Two pilot-scale units of biofiltration were set up. The gaseous mixture was generated to obtain a total TEX concentration of 600 µg m−3. Elimination performance of both biofilters was monitored for 96 days. Microbial behavior and the potential capacity to degrade the NOx, were investigated. RESULTS: The removal efficiency (RE) was 30% in the non-planted and 15% in the planted biofilter at day 3. The RE decreased more rapidly in planted biofilter than in non-planted until nutrient addition at day 77. Consequently, the RE increased to 70% in both reactors. The potential for carbon mineralization was higher than those found in soils. The denitrification activity indicated good conditions for synthesis and maintenance of the denitrifying enzyme pool in the mound of soil. This suggested that NOx could also be treated in such a system. CONCLUSION: The efficiency of the planted biofilters in removing TEX was evaluated and found to have good potential for improving air quality. Copyright © 2012 Society of Chemical Industr

Denitrification in the upper vadose zone layers: a comparison between a fluvic hypercalcaric cambisol and a haplic calcisol

The vertical distributions of heterotrophs, NO$_{3}^{-}$-reducers and denitrifiers, specific respiratory and denitrifying activities were studied in the upper vadose zone of two profiles, distinguished from each other by the risk of transitory anaerobic conditions. According to pedological observations, 3 and 4 layers were defined in the fluvic hypercalcaric cambisol and haplic calcisol profiles, respectively. Bacterial enumerations were performed using the Most Probable Number (MPN) method. Aerobic respiratory and denitrifying activities were estimated from the depletion of O$_{2}$ and the accumulation of N$_{2}$O in the presence of C$_{2}$H$_{2}$, respectively, for soil in sealed flasks incubated in optimal conditions. The denitrifier - to - heterotroph ratio indicates that the denitrifying ability favors micro-organisms in the competition for deep layer colonization in the poorly aerated site. Whereas specific aerobic respiration does not vary or increase with depth, the specific denitrifying activity decreases with depth and is mostly affected by organic-C in the poorly aerated site. The use of specific denitrifying activity should be accounted for in models of denitrification.Dénitrification dans la zone non saturée superficielle : comparaison entre un fluvic hypercalcaric cambisol et un haplic calcisol. Dans cette étude les distributions verticales des micro-organismes hétérotrophes, des réducteurs de nitrate et des dénitrifiants, ainsi que de leurs activités spécifiques respiratoires et dénitrifiantes, ont été comparées dans la zone non saturée superficielle de deux sites se distinguant par le risque de conditions anoxiques transitoires. Suite à une caractérisation pédologique, 3 et 4 horizons ont été distingués respectivement aux niveaux d'un fluvic hypercalcaric cambisol et d'un haplic calcisol. Les nombres de bactéries ont été estimés par la méthode du nombre le plus probable (MPN). Les activités respiratoire aérobie et dénitrifiante ont été caractérisées par le suivi respectif de la disparition de O$_2$ ou de l'accumulation de N$_2$O en présence de C$_2$H$_2$, pour du sol incubé en conditions optimales à l'intérieur de flacons scellés. Le rapport dénitrifiants/hétérotrophes indique que l'aptitude à dénitrifier donne un avantage dans la compétition pour coloniser les horizons profonds du site le moins bien aéré. Alors que l'activité respiratoire aérobie spécifique semble constante ou s'accroître avec la profondeur, l'activité spécifique dénitrifiante décroît. Elle est affectée par le C-organique plus faible dans le site moins aéré. L'introduction de l'activité spécifique dénitrifiante dans les modèles de dénitrification pourrait améliorer les prédictions de concentration en NO$_3^{-}$ arrivant à la nappe

Combined study of titanium dioxide nanoparticle transport and toxicity on microbial nitrifying communities under single and repeated exposures in soil columns

Soils are exposed to nanoparticles (NPs) as a result of their increasing use in many commercial products. Adverse effects of NPs on soil microorganisms have, been reported in several ecotoxicological studies using microcosms. Although repeated exposures are more likely to occur in soils, most of these previous studies were performed as a single exposure to NPs. Contrary to single, contamination, the study of multiple NP contaminations in soils requires the use of specialized setups. Using a soil column experiment, we compared the influence of single and repeated exposures (one, two, or three exposures that resulted in the same final concentration applied) on the transport of titanium dioxide (TiO2) NPs through soil and the effect of these different exposure scenarios on the abundance and activity of soil nitrifying microbial communities after a 2 month incubation. The transport of TiO2 NPs was very limited under both single and repeated exposures and was highest for the lowest concentration injected during the first application. Significant decreases in nitrification-activity and ammonia-oxidizing archaea and bacteria populations were observed only for the repeated exposure scenario (three TiO2 NP contaminations). These results suggest that, under repeated exposures, the transport of TiO2 NPs to deep soil layers and groundwater is limited and that a chronic contamination is more harmful for the soil microbiological functioning than a single exposure

Denitrification in the upper vadose zone layers: a comparison between a fluvic hypercalcaric cambisol and a haplic calcisol

International audienceThe vertical distributions of heterotrophs, NO 3--reducers and denitrifiers, specific respiratory and denitrifying activities were studied in the upper vadose zone of two profiles, distinguished from each other by the risk of transitory anaerobic conditions. According to pedological observations, 3 and 4 layers were defined in the fluvic hypercalcaric cambisol and haplic calcisol profiles, respectively. Bacterial enumerations were performed using the Most Probable Number (MPN) method. Aerobic respiratory and denitrifying activities were estimated from the depletion of O 2 and the accumulation of N 2O in the presence of C 2H 2, respectively, for soil in sealed flasks incubated in optimal conditions. The denitrifier - to - heterotroph ratio indicates that the denitrifying ability favors micro-organisms in the competition for deep layer colonization in the poorly aerated site. Whereas specific aerobic respiration does not vary or increase with depth, the specific denitrifying activity decreases with depth and is mostly affected by organic-C in the poorly aerated site. The use of specific denitrifying activity should be accounted for in models of denitrificationDénitrification dans la zone non saturée superficielle : comparaison entre un fluvic hypercalcaric cambisol et un haplic calcisol . Dans cette étude les distributions verticales des micro-organismes hétérotrophes, des réducteurs de nitrate et des dénitrifiants, ainsi que de leurs activités spécifiques respiratoires et dénitrifiantes, ont été comparées dans la zone non saturée superficielle de deux sites se distinguant par le risque de conditions anoxiques transitoires. Suite à une caractérisation pédologique, 3 et 4 horizons ont été distingués respectivement aux niveaux d'un fluvic hypercalcaric cambisol et d'un haplic calcisol. Les nombres de bactéries ont été estimés par la méthode du nombre le plus probable (MPN). Les activités respiratoire aérobie et dénitrifiante ont été caractérisées par le suivi respectif de la disparition de O 2 ou de l'accumulation de N 2O en présence de C 2H 2, pour du sol incubé en conditions optimales à l'intérieur de flacons scellés. Le rapport dénitrifiants/hétérotrophes indique que l'aptitude à dénitrifier donne un avantage dans la compétition pour coloniser les horizons profonds du site le moins bien aéré. Alors que l'activité respiratoire aérobie spécifique semble constante ou s'accroître avec la profondeur, l'activité spécifique dénitrifiante décroît. Elle est affectée par le C-organique plus faible dans le site moins aéré. L'introduction de l'activité spécifique dénitrifiante dans les modèles de dénitrification pourrait améliorer les prédictions de concentration en NO 3- arrivant à la nappe

Influence of soil properties on the toxicity of TiO₂ nanoparticles on carbon mineralization and bacterial abundance

Information regarding the impact of low concentration of engineered nanoparticles on soil microbial communities is currently limited and the importance of soil characteristics is often neglected in ecological risk assessment. To evaluate the impact of TiO2 nanoparticles (NPs) on soil microbial communities (measured on bacterial abundance and carbon mineralization activity), 6 agricultural soils exhibiting contrasted textures and organic matter contents were exposed for 90 days to a low environmentally relevant concentration or to an accidental spiking of TiO2-NPs (1 and 500mgkg(-1) dry soil, respectively) in microcosms. In most soils, TiO2-NPs did not impact the activity and abundance of microbial communities, except in the silty-clay soil (high OM) where C-mineralization was significantly lowered, even with the low NPs concentration. Our results suggest that TiO2-NPs toxicity does not depend on soil texture but likely on pH and OM content. We characterized TiO2-NPs aggregation and zeta potential in soil solutions, in order to explain the difference of TiO2-NPs effects on soil C-mineralization. Zeta potential and aggregation of TiO2-NPs in the silty-clay (high OM) soil solution lead to a lower stability of TiO2-NP-aggregates than in the other soils. Further experiments would be necessary to evaluate the relationship between TiO2-NPs stability and toxicity in the soil