International audience | Assessing the ecological risk of combined pollution, especially from a holistic perspective with the consideration of the overarching functions of soil ecosystem, is crucial and beneficial to the improvement of ecological risk assessment (ERA) framework. In this study, four soils with similar physicochemical properties but contrasting heavy metals contamination levels were selected to explore changes in the integrated functional sensitivity (MSI), resistance (MRS) and resilience (MRL) of soil microbial communities subjected to herbicide siduron, based on which the ecological risk of the accumulation of siduron in the four studied soils were evaluated. The results suggested that the microbial biomass carbon, activity of denitrification enzyme and nitrogenase were indicative of MSI and MRS, and the same three parameters plus soil basal respiration were indicative of MRL. Significant dose-effect relationships between siduron residues in soils and MSI, MRS and MRL under combined pollution were observed. Heavy metal polluted soils showed higher sensitivity and lower resistance to the additional disturbance of herbicide siduron due to the lower microbial biomass, while the resilience of heavy metal polluted soils was much higher due to the pre-adaption to the chemical stresses. The quantifiable indicator microbial functional stability was incorporated in the framework of ERA and the results showed that the accumulation of siduron in the studied soils could exhibit potential harm to the integrated functional stability of soil microbial community. Thus, this work provides insights into the application of integrated function of soil microbial community into the framework of ERA.

International audience | Assessing the ecological risk of combined pollution, especially from a holistic perspective with the consideration of the overarching functions of soil ecosystem, is crucial and beneficial to the improvement of ecological risk assessment (ERA) framework. In this study, four soils with similar physicochemical properties but contrasting heavy metals contamination levels were selected to explore changes in the integrated functional sensitivity (MSI), resistance (MRS) and resilience (MRL) of soil microbial communities subjected to herbicide siduron, based on which the ecological risk of the accumulation of siduron in the four studied soils were evaluated. The results suggested that the microbial biomass carbon, activity of denitrification enzyme and nitrogenase were indicative of MSI and MRS, and the same three parameters plus soil basal respiration were indicative of MRL. Significant dose-effect relationships between siduron residues in soils and MSI, MRS and MRL under combined pollution were observed. Heavy metal polluted soils showed higher sensitivity and lower resistance to the additional disturbance of herbicide siduron due to the lower microbial biomass, while the resilience of heavy metal polluted soils was much higher due to the pre-adaption to the chemical stresses. The quantifiable indicator microbial functional stability was incorporated in the framework of ERA and the results showed that the accumulation of siduron in the studied soils could exhibit potential harm to the integrated functional stability of soil microbial community. Thus, this work provides insights into the application of integrated function of soil microbial community into the framework of ERA.

This is the post-print version of the following article: "Massive plastic pollution in a mega-river of a developing country: Sediment deposition and ingestion by fish (Prochilodus lineatus)", which has been published in final form at https://www.sciencedirect.com/science/article/pii/S0269749119328520 | International audience | The aim of this study was to determine the amount, composition and origin of plastic debris in one of the world largest river, the Paraná River in Argentina (South America), focusing on the impact of urban rivers, relationships among macro, meso and microplastic, socio-political issues and microplastic ingestion by fish.

The aim of this study was to determine the amount, composition and origin of plastic debris in one of the world largest river, the Paraná River in Argentina (South America), focusing on the impact of urban rivers, relationships among macro, meso and microplastic, socio-political issues and microplastic ingestion by fish.We recorded a huge concentration of macroplastic debris of domestic origin (up to 5.05 macroplastic items per m2) dominated largely by bags (mainly high- and low-density polyethylene), foodwrapper (polypropylene and polystyrene), foam plastics (expanded polystyrene) and beverage bottles (polyethylene terephthalate), particularly downstream from the confluence with an urban stream. This suggests inadequate waste collection, processing and final disposal in the region, which is regrettably recurrent in many cities of the Global South and Argentina in particular.We found an average of 4654 microplastic fragments m−2 in shoreline sediments of the river, ranging from 131 to 12687 microplastics m−2. In contrast to other studies from industrialized countries from Europe and North America, secondary microplastics (resulting from comminution of larger particles) were more abundant than primary ones (microbeads to cosmetics or pellets to the industry). This could be explained by differences in consumer habits and industrialization level between societies and economies.Microplastic particles (mostly fibres) were recorded in the digestive tract of 100% of the studied Prochilodus lineatus (commercial species).Contrary to recently published statements by other researchers, our results suggest neither macroplastic nor mesoplastics would serve as surrogate for microplastic items in pollution surveys, suggesting the need to consider all three size categories.The massive plastic pollution found in the Paraná River is caused by an inadequate waste management. New actions are required to properly manage waste from its inception to its final disposal.

International audience | Mercury pollution is currently a major public health concern, given the adverse effects of mercury on wildlife and humans. Soil plays an essential role in speciation of mercury and its global cycling, while being a habitat for a wide range of terrestrial fauna. Soil fauna, primarily soil-feeding taxa that are in intimate contact with soil pollutants are key contributors in the cycling of soil mercury and might provide relevant indications about soil pollution. We studied the enrichment of various mercury species in the nests and bodies of soil-feeding termites Silvestritermes spp. in French Guiana. Soil-feeding termites are the only social insects using soil as both shelter and food and are major decomposers of organic matter in neotropical forests. Nests of S. minutus were depleted in total and mobile mercury compared to nearby soil. In contrast, they were enriched 17 times in methylmercury. The highest concentrations of methylmercury were found in body of both studied termite species, with mean bioconcentration factors of 58 for S. minutus and 179 for S. holmgreni relative to the soil. The assessment of the body distribution of methylmercury in S. minutus showed concentrations of 221 ng g−1 for the guts and even higher for the gut-free carcasses (683 ng g−1), suggesting that methylmercury is not confined to the gut where it was likely produced, but rather stored in various tissues. This enrichment in the most toxic form of Hg in termites may be of concern on termite predators and the higher levels in the food chain that may be endangered through prey-to-predator transfers and bioaccumulation. Soil-feeding termites appear to be promising candidates as bio-indicators of mercury pollution in soils of neotropical rainforest ecosystems.

Mercury pollution is currently a major public health concern, given the adverse effects of mercury on wildlife and humans. Soil plays an essential role in speciation of mercury and its global cycling, while being a habitat for a wide range of terrestrial fauna. Soil fauna, primarily soil-feeding taxa that are in intimate contact with soil pollutants are key contributors in the cycling of soil mercury and might provide relevant indications about soil pollution. We studied the enrichment of various mercury species in the nests and bodies of soil-feeding termites Silvestritermes spp. in French Guiana. Soil-feeding termites are the only social insects using soil as both shelter and food and are major decomposers of organic matter in neotropical forests. Nests of S. minutus were depleted in total and mobile mercury compared to nearby soil. In contrast, they were enriched 17 times in methylmercury. The highest concentrations of methylmercury were found in body of both studied termite species, with mean bioconcentration factors of 58 for S. minutus and 179 for S. holmgreni relative to the soil. The assessment of the body distribution of methylmercury in S. minutus showed concentrations of 221 ng g⁻¹ for the guts and even higher for the gut-free carcasses (683 ng g⁻¹), suggesting that methylmercury is not confined to the gut where it was likely produced, but rather stored in various tissues. This enrichment in the most toxic form of Hg in termites may be of concern on termite predators and the higher levels in the food chain that may be endangered through prey-to-predator transfers and bioaccumulation. Soil-feeding termites appear to be promising candidates as bio-indicators of mercury pollution in soils of neotropical rainforest ecosystems.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples | International audience | Bed sediments and a dated sediment core were collected upstream and downstream from the city of Lyon (France) to assess the spatial and temporal trends of contamination by per- and polyfluoroalkyl substances (PFASs) in this section of the Rhône River. Upstream from Lyon, concentrations of total PFASs (ΣPFASs) in sediments are low (between 0.19 and 2.6 ng g−1 dry weight - dw), being characterized by a high proportion of perfluorooctane sulfonate (PFOS). Downstream from Lyon, and also from a fluoropolymer manufacturing plant, ΣPFASs concentrations reach 48.7 ng g−1 dw. A gradual decrease of concentrations is reported at the coring site further downstream (38 km). Based on a dated sediment core, the temporal evolution of PFASs is reconstructed from 1984 to 2013. Prior to 1987, ΣPFASs concentrations were low (≤2 ng g−1 dw), increasing to a maximum of 51 ng g−1 dw in the 1990s and then decreasing from 2002 to the present day (∼10 ng g−1 dw). In terms of the PFAS pattern, the proportion of perfluoroalkyl sulfonic acids (PFSAs) has remained stable since the 1980s (∼10%), whereas large variations are reported for carboxylic acids (PFCAs). Long chain- (C > 8) PFCAs characterized by an even number of perfluorinated carbons represent about 74% of the total PFAS load until 2005. However, from 2005 to 2013, the relative contribution of long chain- (C > 8) PFCAs with an odd number of perfluorinated carbons reaches 80%. Such changes in the PFAS pattern likely highlight a major shift in the industrial production process. This spatial and retrospective study provides valuable insights into the long-term contamination patterns of PFAS chemicals in river basins impacted by both urban and industrial activities.

Bed sediments and a dated sediment core were collected upstream and downstream from the city of Lyon (France) to assess the spatial and temporal trends of contamination by per- and polyfluoroalkyl substances (PFASs) in this section of the Rhône River. Upstream from Lyon, concentrations of total PFASs (ΣPFASs) in sediments are low (between 0.19 and 2.6 ng g⁻¹ dry weight - dw), being characterized by a high proportion of perfluorooctane sulfonate (PFOS). Downstream from Lyon, and also from a fluoropolymer manufacturing plant, ΣPFASs concentrations reach 48.7 ng g⁻¹ dw. A gradual decrease of concentrations is reported at the coring site further downstream (38 km). Based on a dated sediment core, the temporal evolution of PFASs is reconstructed from 1984 to 2013. Prior to 1987, ΣPFASs concentrations were low (≤2 ng g⁻¹ dw), increasing to a maximum of 51 ng g⁻¹ dw in the 1990s and then decreasing from 2002 to the present day (∼10 ng g⁻¹ dw). In terms of the PFAS pattern, the proportion of perfluoroalkyl sulfonic acids (PFSAs) has remained stable since the 1980s (∼10%), whereas large variations are reported for carboxylic acids (PFCAs). Long chain- (C > 8) PFCAs characterized by an even number of perfluorinated carbons represent about 74% of the total PFAS load until 2005. However, from 2005 to 2013, the relative contribution of long chain- (C > 8) PFCAs with an odd number of perfluorinated carbons reaches 80%. Such changes in the PFAS pattern likely highlight a major shift in the industrial production process. This spatial and retrospective study provides valuable insights into the long-term contamination patterns of PFAS chemicals in river basins impacted by both urban and industrial activities.

Bed sediments and a dated sediment core were collected upstream and downstream from the city of Lyon (France) to assess the spatial and temporal trends of contamination by per- and polyfluoroalkyl substances (PFASs) in this section of the Rhône River. Upstream from Lyon, concentrations of total PFASs (tPFASs) in sediments are low (between 0.19 and 2.6 ng g-1 dry weight - dw), being characterized by a high proportion of perfluorooctane sulfonate (PFOS). Downstream from Lyon, and also from a fluoropolymer manufacturing plant, tPFASs concentrations reach 48.7 ng g-1 dw. A gradual decrease of concentrations is reported at the coring site further downstream (38 km). Based on a dated sediment core, the temporal evolution of PFASs is reconstructed from 1984 to 2013. Prior to 1987, tPFASs concentrations were low (≤ 2 ng g-1 dw), increasing to a maximum of 51 ng g-1 dw in the 1990s and then decreasing from 2002 to the present day (~10 ng g-1 dw). In terms of the PFAS pattern, the proportion of perfluoroalkyl sulfonic acids (PFSAs) has remained stable since the 1980s (~10%), whereas large variations are reported for carboxylic acids (PFCAs). Long chain- (C>8) PFCAs characterized by an even number of perfluorinated carbons represent about 74% of the total PFAS load until 2005. However, from 2005 to 2013, the relative contribution of long chain- (C>8) PFCAs with an odd number of perfluorinated carbons reaches 80%. Such changes in the PFAS pattern likely highlight a major shift in the industrial production process. This spatial and retrospective study provides valuable insights into the long-term contamination patterns of PFAS chemicals in river basins impacted by both urban and industrial activities.

International audience | While numerous studies have examined the effect of N deposition on ecosystem N retention, few have analyzed the involvement of plant species and climate warming in this process. We experimentally investigated the effects of increasing N deposition (Nexo) and climate warming on the fate of Nexo in a subalpine meadow and established the involvement of plant species. Using 15N tracer, we tracked Nexo sprayed on the vegetation in belowground and aboveground plant biomasses (AGB) and in bulk soil over three growing seasons. We assessed the Nexo absorption capacity of plant species and the contribution of Nexo to their AGB N pool. The meadow retained a large proportion of Nexo (≈65%, mostly in AGB) for depositions up to four times the background N rate. Nexo present in the meadow compartments in year 2 was still present in year 3, suggesting that the ecosystem was unsaturated after three years of high N input. Nexo retention resulted more from an increase in N concentration in plant tissues than from the increase in AGB. The species-specific Nexo absorption capacity was inversely related to their AGB N concentration. Nexo accounted for up to 40% of total AGB N depending on the species and the N treatments. The contribution of species to ecosystem Nexo retention more contingent on their AGB than on their relative cover in the community, ranked as follows: C. vulgaris (14.0%) > N. stricta (7.0%) > other Poaceae = C. caryophyllea (2.5%) > other Eudicotyledons (1.5%) > non-vascular species = P. erecta > Fabaceae (0.8–0.2%). Climate warming increased AGB and decreased tissue N concentration. No warming-Nexo interaction was observed. Thus, Pyrenean subalpine meadows that have not undergone a decline in plant species richness in recent decades paradoxically display a high potential to sequester atmospheric N deposition.

While numerous studies have examined the effect of N deposition on ecosystem N retention, few have analyzed the involvement of plant species and climate warming in this process. We experimentally investigated the effects of increasing N deposition (Nexo) and climate warming on the fate of Nexo in a subalpine meadow and established the involvement of plant species. Using 15N tracer, we tracked Nexo sprayed on the vegetation in belowground and aboveground plant biomasses (AGB) and in bulk soil over three growing seasons. We assessed the Nexo absorption capacity of plant species and the contribution of Nexo to their AGB N pool. The meadow retained a large proportion of Nexo (≈65%, mostly in AGB) for depositions up to four times the background N rate. Nexo present in the meadow compartments in year 2 was still present in year 3, suggesting that the ecosystem was unsaturated after three years of high N input. Nexo retention resulted more from an increase in N concentration in plant tissues than from the increase in AGB. The species-specific Nexo absorption capacity was inversely related to their AGB N concentration. Nexo accounted for up to 40% of total AGB N depending on the species and the N treatments. The contribution of species to ecosystem Nexo retention more contingent on their AGB than on their relative cover in the community, ranked as follows: C. vulgaris (14.0%) > N. stricta (7.0%) > other Poaceae = C. caryophyllea (2.5%) > other Eudicotyledons (1.5%) > non-vascular species = P. erecta > Fabaceae (0.8–0.2%). Climate warming increased AGB and decreased tissue N concentration. No warming-Nexo interaction was observed. Thus, Pyrenean subalpine meadows that have not undergone a decline in plant species richness in recent decades paradoxically display a high potential to sequester atmospheric N deposition.