International audience | Siderophores are chelators with a high selectivity for Fe(III) and a good affinity for divalent metals, including Cd(II) and Ni(II). Inoculation with siderophore-producing bacteria (SPB) has thus been proposed as an alternative to chelator supply in phytoremediation. Accurate assessments of the potential of this association require a dissection of the interaction of siderophores with metals at the soil–root interface. This study focuses on pyoverdine (Pvd), the main siderophore produced by Pseudomonas aeruginosa. We first assessed the ability of Pvd to coordinate Ni(II). The stability constant of Pvd–Ni(II) (log K L′Ni = 10.9) was found to be higher than that of Pvd–Cd(II) (log K L′Cd = 8.2). We then investigated the effect of a direct supply of Pvd on the mobilization, speciation, and phytoavailability of Cd and Ni in hydroponics. When supplied at a concentration of 50 μM, Pvd selectively promoted Ni mobilization from smectite. It decreased plant Ni and Cd contents and the free ionic fractions of these two metals, consistent with the free ion activity model. Pvd had a more pronounced effect for Ni than for Cd, as predicted from its coordination properties. Inoculation with P. aeruginosa had a similar effect on Ni phytoavailability to the direct supply of Pvd.

Siderophores are chelators with a high selectivity for Fe(III) and a good affinity for divalent metals, including Cd(II) and Ni(II). Inoculation with siderophore-producing bacteria (SPB) has thus been proposed as an alternative to chelator supply in phytoremediation. Accurate assessments of the potential of this association require a dissection of the interaction of siderophores with metals at the soil–root interface. This study focuses on pyoverdine (Pvd), the main siderophore produced by Pseudomonas aeruginosa. We first assessed the ability of Pvd to coordinate Ni(II). The stability constant of Pvd–Ni(II) (log K ᴸ′ᴺⁱ = 10.9) was found to be higher than that of Pvd–Cd(II) (log K ᴸ′Cᵈ = 8.2). We then investigated the effect of a direct supply of Pvd on the mobilization, speciation, and phytoavailability of Cd and Ni in hydroponics. When supplied at a concentration of 50 μM, Pvd selectively promoted Ni mobilization from smectite. It decreased plant Ni and Cd contents and the free ionic fractions of these two metals, consistent with the free ion activity model. Pvd had a more pronounced effect for Ni than for Cd, as predicted from its coordination properties. Inoculation with P. aeruginosa had a similar effect on Ni phytoavailability to the direct supply of Pvd.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA | International audience | Streams located in vineyard areas are particularly exposed to mixtures of dissolved and particulate contaminants such as metals and organic pesticides. In this context, phototrophic biofilms are increasingly used as indicators of river water contaminations through pollution-induced community tolerance (PICT) assessments based on short-term toxicity tests with individual or mixtures of toxicants. We conducted a laboratory experiment to evaluate the relative influence of the dissolved and particulate fractions on the effects of metals and pesticides on phototrophic biofilms in a context of contamination from a vineyard watershed. Three sets of artificial channels were supplied with (i) unfiltered water from a stream reference site, (ii) unfiltered water from a stream contaminated site, and (iii) filtered water (0.45 microm) from the same contaminated site. Biofilm growth, diatom community structure, and dissolved toxicant concentrations differed slightly between channels supplied with unfiltered or filtered water from the contaminated site. However, PICT assessments with individual toxicants or mixtures of toxicants extracted from passive samplers suggested no significant difference in tolerance to metals and organic pesticides between phototrophic communities supplied with unfiltered or filtered contaminated water. Our results confirm the use of extracts from passive samplers as a promising approach in short-term toxicity tests to characterize impacts of contamination on aquatic communities.

Streams located in vineyard areas are particularly exposed to mixtures of dissolved and particulate contaminants such as metals and organic pesticides. In this context, phototrophic biofilms are increasingly used as indicators of river water contaminations through pollution-induced community tolerance (PICT) assessments based on short-term toxicity tests with individual or mixtures of toxicants. We conducted a laboratory experiment to evaluate the relative influence of the dissolved and particulate fractions on the effects of metals and pesticides on phototrophic biofilms in a context of contamination from a vineyard watershed. Three sets of artificial channels were supplied with (i) unfiltered water from a stream reference site, (ii) unfiltered water from a stream contaminated site, and (iii) filtered water (0.45 μm) from the same contaminated site. Biofilm growth, diatom community structure, and dissolved toxicant concentrations differed slightly between channels supplied with unfiltered or filtered water from the contaminated site. However, PICT assessments with individual toxicants or mixtures of toxicants extracted from passive samplers suggested no significant difference in tolerance to metals and organic pesticides between phototrophic communities supplied with unfiltered or filtered contaminated water. Our results confirm the use of extracts from passive samplers as a promising approach in short-term toxicity tests to characterize impacts of contamination on aquatic communities.

International audience | Overall recruitment of European glass eels (Anguilla anguilla) has decreased significantly since the early 1980s. Due to their long life cycle, benthic/demersal habits and high lipid content, eels might accumulate high concentrations of contaminants, but data concerning glass eels are still scarce. This study provides original data on methylmercury (MeHg) concentrations in glass eels at spatial (marine and estuarine), annual and seasonal scales. The relationship between MeHg concentrations in glass eels and their propensity to migrate up estuaries was also investigated. MeHg data were individually related to the eels’ energetic condition which was estimated by dry weight. Glass eel migratory behaviour was investigated in an experimental flume and related to the MeHg concentration and dry weight at the individual scale. Marine and estuarine glass eels were caught from 2004 to 2011. There was a strong inverse correlation between MeHg concentrations and dry weight. MeHg concentrations increased in marine and estuarine glass eels from 2004 to 2009 and from 2004 to 2010, respectively, and then, both groups decreased in 2011. On a seasonal time scale, MeHg concentrations were higher at the end of the fishing season (April). MeHg bioaccumulation is likely to result from different sources, but the lack of significant differences between marine and estuarine glass eels suggests that direct contamination during estuarine migration is low. Other sources such as maternal transfer or oceanic contamination are discussed

Overall recruitment of European glass eels (Anguilla anguilla) has decreased significantly since the early 1980s. Due to their long life cycle, benthic/demersal habits and high lipid content, eels might accumulate high concentrations of contaminants, but data concerning glass eels are still scarce. This study provides original data on methylmercury (MeHg) concentrations in glass eels at spatial (marine and estuarine), annual and seasonal scales. The relationship between MeHg concentrations in glass eels and their propensity to migrate up estuaries was also investigated. MeHg data were individually related to the eels’ energetic condition which was estimated by dry weight. Glass eel migratory behaviour was investigated in an experimental flume and related to the MeHg concentration and dry weight at the individual scale. Marine and estuarine glass eels were caught from 2004 to 2011. There was a strong inverse correlation between MeHg concentrations and dry weight. MeHg concentrations increased in marine and estuarine glass eels from 2004 to 2009 and from 2004 to 2010, respectively, and then, both groups decreased in 2011. On a seasonal time scale, MeHg concentrations were higher at the end of the fishing season (April). MeHg bioaccumulation is likely to result from different sources, but the lack of significant differences between marine and estuarine glass eels suggests that direct contamination during estuarine migration is low. Other sources such as maternal transfer or oceanic contamination are discussed.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA | International audience | Pollution-induced community tolerance (PICT) approaches involve comparing tolerance levels of natural communities to a particular contaminant or a contaminant mixture using short-term toxicity tests performed under controlled conditions. However, results from toxicity tests can be modulated by various environmental and experimental conditions, raising questions about their reproducibility and comparability. In this context, the present study aimed to determine the influence of exposure duration, periphyton suspension concentration and periphyton maturation stage on the measurement of short-term effects of copper on phototrophic periphyton communities. Our results showed the very weak influence of exposure duration in the tested range (2-6 h) on toxicity level, whereas periphyton biomass in the tested suspension (in terms of both chlorophyll a concentrations and dry weight), proved a crucial determinant in toxicity assessment. Results also highlighted the potential tolerance increase with the periphyton maturation stage. This parameter conditioned the positive linear relationship between tolerance level and periphyton suspension concentration, leading to an increase in the linear regression slope with the maturation stage. This suggests that such a relationship is probably highly periphyton-dependent. Consequently, to enable data toxicity comparisons, an a priori normalization of the periphyton suspension biomass is necessary, and PICT approaches require the use, as much of possible, of periphyton with similar maturation stage. Finally, the present study clearly shows that a better standardization of PICT approaches could help to improve reproducibility. It could thus facilitate the comparison of tolerance levels measured in the same study (e.g. spatial and/or temporal and/or inter-treatment comparison) as well as the comparison obtained from different experimental and in situ research.

Pollution-induced community tolerance (PICT) approaches involve comparing tolerance levels of natural communities to a particular contaminant or a contaminant mixture using short-term toxicity tests performed under controlled conditions. However, results from toxicity tests can be modulated by various environmental and experimental conditions, raising questions about their reproducibility and comparability. In this context, the present study aimed to determine the influence of exposure duration, periphyton suspension concentration, and periphyton maturation stage on the measurement of short-term effects of copper on phototrophic periphyton communities. Our results showed the very weak influence of exposure duration in the tested range (2–6 h) on toxicity level, whereas periphyton biomass in the tested suspension (in terms of both chlorophyll a concentrations and dry weight), proved a crucial determinant in toxicity assessment. Results also highlighted the potential tolerance increase with the periphyton maturation stage. This parameter conditioned the positive linear relationship between tolerance level and periphyton suspension concentration, leading to an increase in the linear regression slope with the maturation stage. This suggests that such a relationship is probably highly periphyton-dependent. Consequently, to enable data toxicity comparisons, an a priori normalization of the periphyton suspension biomass is necessary, and PICT approaches require the use, as much of possible, of periphyton with similar maturation stage. Finally, the present study clearly shows that a better standardization of PICT approaches could help to improve reproducibility. It could thus facilitate the comparison of tolerance levels measured in the same study (e.g., spatial and/or temporal and/or inter-treatment comparison) as well as the comparison obtained from different experimental and in situ research.