International audience | At present, some triazine herbicides occurrence in European groundwater, 13 years after their use ban in the European Union, remains of great concern and raises the question of their persistence in groundwater systems due to several factors such as storage and remobilization from soil and unsaturated zone, limited or absence of degradation, sorption insaturated zones, or to continuing illegal applications. In order to address this problem and to determine triazine distribution in the saturated zone, their occurrence is investigated in the light of the aquifer hydrodynamic on the basis of a geochemical approach using groundwater dating tracers (3H/3He). In this study, atrazine, simazine, terbuthylazine, deethylatrazine, deisopropylatrazine, and deethylterbuthylazine are measured in 66 samples collected between 2011 and 2013 from 21 sampling points, on the Vistrenque shallow alluvial aquifer (southern France), covered by a major agricultural land use. The frequencies of quantification range from 100 to 56 % for simazine and atrazine, respectively (LQ = 1 ng L−1). Total triazine concentrations vary between 15 and 350 ng L−1 and show three different patterns with depth below the water table : (1) low concentrations independent of depth but related to water origin, (2) an increase in concentrations with depth in the aquifer related to groundwater residence time and triazine use prior to their ban, and (3) relatively high concentrations at low depths in the saturated zone more likely related to a slow desorption of these compounds from the soil and unsaturated zone. The triazine attenuation rate varies between 0.3 for waters influenced by surface water infiltration and 4.8 for water showing longer residence times in the aquifer, suggesting an increase in these rates with water residence time in the saturated zone. Increasing triazine concentrations with depth is consistent with a significant decrease in the use of these pesticides for the last 10 years on this area and highlights the efficiency of their ban.

At present, some triazine herbicides occurrence in European groundwater, 13 years after their use ban in the European Union, remains of great concern and raises the question of their persistence in groundwater systems due to several factors such as storage and remobilization from soil and unsaturated zone, limited or absence of degradation, sorption in saturated zones, or to continuing illegal applications. In order to address this problem and to determine triazine distribution in the saturated zone, their occurrence is investigated in the light of the aquifer hydrodynamic on the basis of a geochemical approach using groundwater dating tracers (³H/³He). In this study, atrazine, simazine, terbuthylazine, deethylatrazine, deisopropylatrazine, and deethylterbuthylazine are measured in 66 samples collected between 2011 and 2013 from 21 sampling points, on the Vistrenque shallow alluvial aquifer (southern France), covered by a major agricultural land use. The frequencies of quantification range from 100 to 56 % for simazine and atrazine, respectively (LQ = 1 ng L⁻¹). Total triazine concentrations vary between 15 and 350 ng L⁻¹ and show three different patterns with depth below the water table: (1) low concentrations independent of depth but related to water origin, (2) an increase in concentrations with depth in the aquifer related to groundwater residence time and triazine use prior to their ban, and (3) relatively high concentrations at low depths in the saturated zone more likely related to a slow desorption of these compounds from the soil and unsaturated zone. The triazine attenuation rate varies between 0.3 for waters influenced by surface water infiltration and 4.8 for water showing longer residence times in the aquifer, suggesting an increase in these rates with water residence time in the saturated zone. Increasing triazine concentrations with depth is consistent with a significant decrease in the use of these pesticides for the last 10 years on this area and highlights the efficiency of their ban.

Oil spills pose a threat to aquatic organisms. However, the physiological effects of crude oil on cardiac function and on thermal tolerance of juvenile fish are still poorly understood. Consequently, in this paper, we will present results of two separate experiments where we exposed juvenile rainbow trout and European sea bass to crude oil and made cardiac thermal tolerances and maximum heart rate (fHmax) measurements after 1 week (rainbow trout) and 6-month recovery (sea bass). In both species, the fHmax was lower in crude oil-exposed fish than in the control ones at temperatures below the optimum but this difference disappeared at higher temperatures. More importantly, the oil-exposed fish had significantly higher Arrhenius break point temperature for fHmax, which gave an estimate for optimum temperature, than the control fish in both species even though the exposure conditions and recovery times differed between species. The results indicated that exposure of juvenile fish to crude oil did not have a significant negative impact upon their cardiac performance in high temperatures and upper thermal tolerance increased when the fish were tested 1 week or 6 months after the exposure. Our findings suggest that the cardiac function and thermal tolerance of juvenile fish are relatively resistant to a crude oil exposure.

Oil spills pose a threat to aquatic organisms. However, the physiological effects of crude oil on cardiac function and on thermal tolerance of juvenile fish are still poorly understood. Consequently, in this paper, we will present results of two separate experiments where we exposed juvenile rainbow trout and European sea bass to crude oil and made cardiac thermal tolerances and maximum heart rate (f Hₘₐₓ) measurements after 1 week (rainbow trout) and 6-month recovery (sea bass). In both species, the f Hₘₐₓ was lower in crude oil-exposed fish than in the control ones at temperatures below the optimum but this difference disappeared at higher temperatures. More importantly, the oil-exposed fish had significantly higher Arrhenius break point temperature for f Hₘₐₓ, which gave an estimate for optimum temperature, than the control fish in both species even though the exposure conditions and recovery times differed between species. The results indicated that exposure of juvenile fish to crude oil did not have a significant negative impact upon their cardiac performance in high temperatures and upper thermal tolerance increased when the fish were tested 1 week or 6 months after the exposure. Our findings suggest that the cardiac function and thermal tolerance of juvenile fish are relatively resistant to a crude oil exposure.

Marine mercury (Hg) concentrations have been monitored in the French coastline for the last half a century using bivalves. The analyses presented in this study concerned 192 samples of bivalves (mussels: Mytilus edulis and Mytilus galloprovincialis and oysters: Crassostrea gigas and Isognomon alatus) from 77 sampling stations along the French coast and in the French Antilles sea. The goals of this study were to assess MeHg levels in various common bivalves from French coastline, and to identify possible geographic, taxonomic or temporal variations of concentrations. We show that the evolution of methylmercury (MeHg) concentrations covary with total mercury (HgT) concentrations. Moreover, in most of the study sites, HgT concentrations have not decreased since 1987, despite regulations to decrease or ban mercury used for anthropic activities.

Marine mercury (Hg) concentrations have been monitored in the French coastline for the last half a century using bivalves. The analyses presented in this study concerned 192 samples of bivalves (mussels: Mytilus edulis and Mytilus galloprovincialis and oysters: Crassostrea gigas and Isognomon alatus) from 77 sampling stations along the French coast and in the French Antilles sea. The goals of this study were to assess MeHg levels in various common bivalves from French coastline, and to identify possible geographic, taxonomic or temporal variations of concentrations. We show that the evolution of methylmercury (MeHg) concentrations covary with total mercury (HgT) concentrations. Moreover, in most of the study sites, HgT concentrations have not decreased since 1987, despite regulations to decrease or ban mercury used for anthropic activities.

We demonstrated the use of a new organometallic nanoprobe for competitive surface-enhanced Raman scattering (SERS) immunoassay devoted to the detection of polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (BaP) in seawater. The nanoprobes are gold nanoparticles (GNPs) labeled by a Raman reporter, the 5,5'-dithiobis(succinimidyl-2-nitrobenzoate) (DSNB) and functionalized with monoclonal antibodies anti-BaP. The antibodies are bound with a high specificity to the analyte while the GNPs enhanced the Raman scattering of the DSNB. This type of immunoassay involved the grafting of BaP onto a sensing surface. Thus, NH2-terminated self-assembled monolayer is formed on the surface of gold substrate using cysteamine. Amines finally reacted with 6-formylbenzo[a]pyrene. So, this SERS detection involves four steps: (i) the nanoprobes are incubated with the sample; (ii) a drop of the mixture is then put onto the substrate; (iii) the surface is rinsed; and (iv) the surface is analyzed by Raman spectroscopy. To synthesize the nanoprobes, firstly, we prepared GNPs according to Frens' method. Then, GNPs were spontaneously labeled by the DSNB Raman reporter, thanks to a strong gold-sulfur interaction. Thereafter, BaP antibodies were cross-linked to the DSNB labeled GNPs by reaction of proteins primary amino groups with N-hydroxyl succinimide (NHS). Before use in SERS detection, their activity was controlled by surface plasmon resonance technique. The present method allows us to detect BaP at trace concentration (2 nmol/L). The results demonstrate that the proposed method has a great potential for application in the monitoring of seawater.

We demonstrated the use of a new organometallic nanoprobe for competitive surface-enhanced Raman scattering (SERS) immunoassay devoted to the detection of polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (BaP) in seawater. The nanoprobes are gold nanoparticles (GNPs) labeled by a Raman reporter, the 5,5′-dithiobis(succinimidyl-2-nitrobenzoate) (DSNB) and functionalized with monoclonal antibodies anti-BaP. The antibodies are bound with a high specificity to the analyte while the GNPs enhanced the Raman scattering of the DSNB. This type of immunoassay involved the grafting of BaP onto a sensing surface. Thus, NH₂-terminated self-assembled monolayer is formed on the surface of gold substrate using cysteamine. Amines finally reacted with 6-formylbenzo[a]pyrene. So, this SERS detection involves four steps: (i) the nanoprobes are incubated with the sample; (ii) a drop of the mixture is then put onto the substrate; (iii) the surface is rinsed; and (iv) the surface is analyzed by Raman spectroscopy. To synthesize the nanoprobes, firstly, we prepared GNPs according to Frens’ method. Then, GNPs were spontaneously labeled by the DSNB Raman reporter, thanks to a strong gold-sulfur interaction. Thereafter, BaP antibodies were cross-linked to the DSNB labeled GNPs by reaction of proteins primary amino groups with N-hydroxyl succinimide (NHS). Before use in SERS detection, their activity was controlled by surface plasmon resonance technique. The present method allows us to detect BaP at trace concentration (2 nmol/L). The results demonstrate that the proposed method has a great potential for application in the monitoring of seawater.

Concerning in situ passive sampler deployment, several technical priorities must be considered. In particular, deployment time must be sufficiently long not only to allow a significant quantity to be accumulated to facilitate analysis but also to ensure that the signal is above the quantification limit and out of the blank influence. Moreover, regarding the diffusive gradient in thin films (DGT) technique, deployment time must also be sufficiently long (at least 5 days) to avoid the interactions of the solutes with the material diffusion layer of the DGT and for the steady state to be reached in the gel. However, biofouling occurs in situ and modifies the surface of the samplers. In this article, we propose a kinetic model which highlights the biofouling effect. This model was able to describe the mitigation of the flux towards the DGT resin observed on Cd, Co, Mn, Ni and Zn during a 22-day deployment in the Seine River. Over a period of 22 days, biofouling had a significant impact on the DGT concentrations measured, which were decreased twofold to threefold when compared to concentrations measured in unaffected DGTs.

Concerning in situ passive sampler deployment, several technical priorities must be considered. In particular, deployment time must be sufficiently long not only to allow a significant quantity to be accumulated to facilitate analysis but also to ensure that the signal is above the quantification limit and out of the blank influence. Moreover, regarding the diffusive gradient in thin films (DGT) technique, deployment time must also be sufficiently long (at least 5 days) to avoid the interactions of the solutes with the material diffusion layer of the DGT and for the steady state to be reached in the gel. However, biofouling occurs in situ and modifies the surface of the samplers. In this article, we propose a kinetic model which highlights the biofouling effect. This model was able to describe the mitigation of the flux towards the DGT resin observed on Cd, Co, Mn, Ni and Zn during a 22-day deployment in the Seine River. Over a period of 22 days, biofouling had a significant impact on the DGT concentrations measured, which were decreased twofold to threefold when compared to concentrations measured in unaffected DGTs.