Cu isotope records of Cu-based antifouling paints in sediment core profiles from the largest European Marina, The Port Camargue.

The intensive use of copper (Cu) compounds as an alternative biocide in antifouling paints (APs) has resulted in wide Cu contamination into the marine environment, especially near marina harbor activities. In this work, the applicability of Cu isotopes to discriminate Cu origins related to the use of Cu-based APs in marine environments was tested. To this, Cu isotopes in APs, shipyard sludges, and sediment cores sampled in the Cu-contaminated Mediterranean marina of Port Camargue were determined. APs represent an important dominant anthropogenic source for metals in this site, making it ideal to test Cu isotopes as tracers. The overall isotope composition of four sediment cores and a surface sample varied between -0.13 and 0.44 ‰ (δ65Cu relative to NIST-976). Selected APs brands show a similar Cu concentration ~0.15 % and δ65Cu average of 0.54 ± 0.05 ‰. The plot of δ65Cu vs concentration for all datasets allowed dissociating natural and APs end-members. However, sample isotope systematics were not consistent with a conservative mixing binary source process. Heavily Cu-contaminated sediments show isotope signatures lighter than APs brands. However, the most Cu-contaminated sample, located directly above the careening area, shows a δ65Cu slightly lighter than APs (0.44 ‰ vs 0.54 ‰, respectively). Results suggest the preferential releasing of a heavy isotope pool by APs when these compounds are solubilized in seawater. The isotope fractionation was attributed to potential chemical Cu coordination changes during its elemental partition between paint and marina seawater and the fractionation induced by the organic ligands in the water column, before deposition. Further laboratory experiments are recommended to model the isotope fractionation mechanisms related to Cu release by APs. Because the APs' isotope signature is modified in marine environments, the use of Cu isotopes as tracers of AP in marine environments is challenging and needs more investigation.

Characterization of the active bacterial community involved in natural attenuation processes in arsenic-rich creek sediments.

Acid mine drainage of the Carnoulès mine (France) is characterized by acid waters containing high concentrations of arsenic and iron. In the first 30 m along the Reigous, a small creek draining the site, more than 38% of the dissolved arsenic was removed by co-precipitation with Fe(III), in agreement with previous studies, which suggest a role of microbial activities in the co-precipitation of As(III) and As(V) with Fe(III) and sulfate. To investigate how this particular ecosystem functions, the bacterial community was characterized in water and sediments by 16S rRNA encoding gene library analysis. Based on the results obtained using a metaproteomic approach on sediments combined with high-sensitivity HPLC-chip spectrometry, several GroEL orthologs expressed by the community were characterized, and the active members of the prokaryotic community inhabiting the creek sediments were identified. Many of these bacteria are ß-proteobacteria such as Gallionella and Thiomonas, but γ-proteobacteria such as Acidithiobacillus ferrooxidans and α-proteobacteria such as Acidiphilium, Actinobacteria, and Firmicutes were also detected.

Predominance of aqueous Tl(I) species in the river system downstream from the abandoned Carnoulès mine (Southern France).

Thallium concentration reached up to 534 µg L(-1) in the Reigous acid mine drainage downstream from the abandoned Pb-Zn Carnoulès mine (Southern France). It decreased to 5.44 µg L(-1) in the Amous River into which the Reigous creek flows. Tl(I) predominated (>98% of total dissolved Tl) over Tl(III), mainly in the form of Tl(+). Small amounts of Tl(III) evidenced in Reigous Creek might be in the form of aqueous TlCl(2)(+). The range of dissolved to particulate distribution coefficients log K(d) = 2.5 L kg(-1) to 4.6 L kg(-1) indicated low affinity of Tl for particles, mainly ferrihydrite, formed in the AMD-impacted watershed. The low retention of Tl(+) on ferrihydrite was demonstrated in sorption experiments, the best fit between experimental and modeled data being achieved for surface complexation constants log K(ads) = -2.67 for strong sites and log K(ads) = -3.76 for weak sites. This new set of constants allowed reasonable prediction of the concentrations of aqueous and particulate Tl resulting from the mixing of water from Reigous Creek and the Amous River water during laboratory experiments, together with those measured in the Amous River field study.

Thermodesulfovibrio hydrogeniphilus sp. nov., a new thermophilic sulphate-reducing bacterium isolated from a Tunisian hot spring.

A new thermophilic sulphate-reducing bacterium (strain Hbr5T) was enriched and isolated from a terrestrial Tunisian hot spring. It was a non-spore-forming Gram-negative curved or vibrio-shaped bacterium. It appeared singly or in long chains and was actively motile by a polar flagellum. It possessed c-type cytochromes and desulfofuscidin. Growth occurred between 50 and 70 degrees C, with an optimum of 65 degrees C at pH 7.1. In the presence of sulphate as a terminal electron acceptor, this strain readily used H2 but formate only poorly. It could use sulphate, thiosulphate, sulphite or arsenate as electron acceptors. Its DNA G+C content was 36.1 mol%. Based on phenotypic, genomic, and phylogenetic characteristics, strain Hbr5T (=DSM 18151T, =JCM 13991T) is proposed to be assigned to a novel species of genus Thermodesulfovibrio, T. hydrogeniphilus sp. nov.

Effects of copper and butyltin compounds on the growth, photosynthetic activity and toxin production of two HAB dinoflagellates: The planktonic Alexandrium catenella and the benthic Ostreopsis cf. ovata.

Controlled laboratory experiments were conducted to test the effects of copper (Cu2+) and butyltins (BuT) on the growth, photosynthetic activity and toxin content of two HABs (Harmful Algal Blooms) dinoflagellates, the planktonic Alexandrium catenella and the benthic Ostreopsis cf. ovata. Microalgae were exposed to increasing concentrations of Cu2+ (10-4 to 31 nM) or BuT (0.084 to 84 nM) for seven days. When considering the growth, EC50 values were 0.16 (±0.09) nM and 0.03 (±0.02) nM of Cu2+ for A. catenella and O. cf. ovata, respectively. Regarding BuT, EC50 was 14.2 (±6) nM for O. cf. ovata, while A. catenella growth inhibition appeared at BuT concentrations ≥27 nM. Photosynthetic activity of the studied dinoflagellates decreased with increasing Cu and BuT concentrations. For O. cf. ovata, the response of this physiological parameter to contamination was less sensitive than the biomass. Cu exposure induced the formation of temporary cysts in both organisms that could resist adverse conditions. The ovatoxin-a and -b concentrations in O. cf. ovata cells increased significantly in the presence of Cu. Altogether, the results suggest a better tolerance of the planktonic A. catenella to Cu and BuT. This could result in a differentiated selection pressure exerted by these metals on phytoplankton species in highly polluted waters. The over-production of toxins in response to Cu stress could pose supplementary health and socio-economic threats in the contaminated marine ecosystems where HABs develop.

Dissolved and bioavailable contaminants in the Seine river basin.

Diffusive Gradient in Thin Films (DGT) and Semi-Permeable Membrane Devices (SPMDs) were deployed in the Seine river basin in order to assess labile metals and truly dissolved Polycyclic Aromatic Hydrocarbons. We show that the tools are reliable in aquatic environments to assess the speciation of dissolved contaminants and hence provide a good insight into the potential bioavailability of contaminants. The deployment of the DGT and SPMDs in contrasting environments in the Seine river basin allowed distinction to be made of availability of contaminants between headwater streams and much more impacted river reaches and an assessment of bioavailability. At the stations under urban influence, the impact of dissolved organic matter on both copper and PAHs bioavailability is less pronounced than at upstream stations, where humic substances dominate.

The environmental legacy of historic Pb-Zn-Ag-Au mining in river basins of the southern edge of the Massif Central (France).

The main rivers (Aude, Orb, Herault) that discharge into the Gulf of Lions and the west bank tributaries of the Rhone River including the Gardon have former non-ferrous metal mines in their upper drainage basin. Using unpublished data and data from the literature, this study provides an integrated overview of the contamination of water and sediment along the continent-sea continuum and of its impacts on the biota and on human health. In the upper part of these basins, water and stream sediments are enriched in metal(-loids) compared to median European concentrations. Arsenic is the main contaminant in the rivers Aude and Gardon d'Anduze, Sb in the Orb and Gardon d'Alès, and Tl in the Herault river. A rapid reduction in dissolved and particulate concentrations was systematically observed along the river due to dilution and precipitation. The high concentrations of metal(-loid)s observed suggest that the former mining activity still represents a potential threat for the environment, but the lack of high temporal resolution monitoring, especially during Mediterranean floods, prevents accurate assessment of metal fluxes from these rivers to the Mediterranean Sea. Studies dedicated to the impacts on human health are too rare, given that studies have shown a higher rate of arsenic-specific cancer near Salsigne mine in the Aude River basin and cases of saturnism in children in the upper Herault River basin. These studies underline the need to take environmental health issues into consideration not only in these watersheds but around the entire Mediterranean basin, which harbors numerous metalliferous ores that have been mined for millennia.

Short-term variability of dissolved trace element concentrations in the Marne and Seine rivers near Paris.

The concentrations of dissolved trace elements (Li, B, Mn, Cu, As, Rb, Sr, Mo, Cd, Ba, Pb) in the Marne and Seine rivers in the Paris urban area were monitored over a 2-year period. The resulting data indicated moderate contamination of waters by the most toxic elements (Cu, As, Cd and Pb). The River Marne upstream and the River Seine downstream of the city of Paris displayed similar concentrations. However higher fluxes of trace elements were observed in the Seine than in the Marne due to their different discharges. Li, B, Rb, Sr and Ba concentrations were correlated with river discharge and concentrations were higher during high river flow. This was interpreted as a dilution by discharge from a major natural or anthropogenic source. Mn, Cu, Mo, Cd and Pb concentrations were not correlated with discharge. Dissolved Mn, Cu and Cd increased rapidly in summer, whereas the concentration of Mo decreased. These variations were attributed to redox processes. During summer when the dissolved oxygen concentrations decrease, Mn, Cu, Cd and Pb are released into solution whereas Mo is immobilised. Like metals, variations in arsenic contents were not linked with discharge. Its similarity with phosphate distribution suggests similar controls involving phytoplankton uptake and release from sediments through organic matter mineralization.

Behaviour of butyltin compounds in the sediment pore waters of a contaminated marina (Port Camargue, South of France).

Despite the ban on tributyltin (TBT) in marine paints, harbour sediments are still highly contaminated by this antifouling agent. Concentrations of TBT and its dealkylated products dibutyltin (DBT) and monobutyltin (MBT) were determined in the pore waters of Port Camargue, a large marina located on the French Mediterranean coast. Pore waters were sampled in the field using peepers deployed in summer 2012 and 2013 and in winter 2012-2013. The winter surveys were characterized by the presence of sulphides in pore waters from a depth of 5 cm, which was not the case in winter. In summer 2013, TBT was shown to be released into pore waters below the sediment-water interface (SWI) at concentrations of up to 70 ngSn L(-1). This release was also observed in sediment anaerobic incubations and was attributed to the mineralization of the sedimentary organic matter, possible stabilization of TBT by complexation with sulphides, and lower debutylation rates in anoxic than in oxic conditions. In summer 2012, a comparatively lower concentration of TBT (around 20 ngSn L(-1) below the SWI) was measured and the presence of methyltin species was detected. We hypothesize that the differences between the two surveys reflect different microbial activity. In winter 2012-2013, marked by Fe-reducing conditions in the sediments, TBT was released into solution at the SWI at concentrations of up to 40 ngSn L(-1). Sediments are thus a continuing source of TBT for the overlying waters despite the ban on its use for boats in France.

Consequences of contaminant mixture on the dynamics and functional diversity of bacterioplankton in a southwestern Mediterranean coastal ecosystem.

Contamination of coastal environments is often due to a complex mixture of pollutants, sometimes in trace levels, that may have significant effects on diversity and function of organisms. The aim of this study was to evaluate the short-term dynamics of bacterioplankton exposed to natural and artificial mixtures of contaminants. Bacterial communities from a southwestern Mediterranean ecosystem, lagoon and the bay (offshore) of Bizerte were exposed to i) elutriate from resuspension of contaminated sediment, and ii) an artificial mixture of metals and herbicides mimicking the contamination observed during sediment resuspension. Elutriate incubation as well as artificial spiking induced strong enrichments in nutrients (up to 18 times), metals (up to six times) and herbicides (up to 20 times) relative to the in situ concentrations in the offshore station, whereas the increases in contaminants were less marked in the lagoon station. In the offshore waters, the artificial mixture of pollutants provoked a strong inhibition of bacterial abundance, production and respiration and significant modifications of the potential functional diversity of bacterioplankton with a strong decrease of the carbohydrate utilization. In contrast, incubation with elutriate resulted in a stimulation of bacterial activities and abundances, suggesting that the toxic effects of pollutants were modified by the increase in nutrient and DOM concentrations due to the sediment resuspension. The effects of elutriate and the artificial mixture of pollutants on bacterial dynamics and the functional diversity were less marked in the lagoon waters, than in offshore waters, suggesting a relative tolerance of lagoon bacteria against contaminants.

Assessment of copper bioavailability and toxicity in vineyard runoff waters by DPASV and algal bioassay.

The aim of this study was to assess the toxicity of runoff waters in an agricultural multipollution context through an in-depth assessment of copper bioavailability and toxicity. Runoff waters were screened for major ions, metals and diuron. The potential environmental impact of these runoff waters was evaluated using the conventional 72-h growth inhibition test with the green alga Pseudokirchneriella subcapitata. The results suggested that the toxicity detected in the calcareous vineyard field was due to the presence of diuron, whereas the non-calcareous runoff waters were non-toxic. Chemical speciation modelling by MINEQL revealed that most of the copper present in the non-toxic natural runoff waters was complexed by organic matter. These samples were spiked with copper, and then the toxicity and the electrochemically bioavailable copper fraction were measured. Differential pulse anodic stripping voltammetry (DPASV) was used to detect labile complexes and free copper. This combined approach highlighted the presence of some labile copper complexes in samples reaching the EC10-these could have contributed to the copper toxicity.

Antimony isotopic composition in river waters affected by ancient mining activity.

In this study, antimony (Sb) isotopic composition was determined in natural water samples collected along two hydrosystems impacted by historical mining activities: the upper Orb River and the Gardon River watershed (SE, France). Antimony isotope ratio was measured by HG-MC-ICP-MS (Hydride Generation Multi-Collector Inductively Coupled Plasma Mass Spectrometer) after a preconcentration and purification step using a new thiol-cellulose powder (TCP) procedure. The external reproducibility obtained for δ(123)Sb measurements of our in-house Sb isotopic standard solution and a certified reference freshwater was 0.06‰ (2σ). Significant isotopic variations were evident in surface waters from the upper Orb River (-0.06‰≤δ(123)Sb≤+0.11‰) and from the Gardon River watershed (+0.27‰≤δ(123)Sb≤+0.83‰). In particular, streams that drained different former mining sites exploited for Sb or Pb-Zn exhibited contrasted Sb isotopic signature, that may be related to various biogeochemical processes occurring during Sb transfer from rocks, mine wastes and sediments to the water compartment. Nevertheless, Sb isotopic composition appeared to be stable along the Gardon River, which might be attributed to the conservative transport of Sb at distance from mine-impacted streams, due to the relative mobile behavior of Sb(V) in natural oxic waters. This study suggests that Sb isotopic composition could be a useful tool to track pollution sources and/or biogeochemical processes in hydrologic systems.

Contrasted responses of Ruditapes decussatus (filter and deposit feeding) and Loripes lacteus (symbiotic) exposed to polymetallic contamination (Port-Camargue, France).

The use of symbiotic bivalve species to assess the effect of anthropogenic metal pollution was rarely investigated whereas data on filter feeding bivalves are common. The aim of this study was the exposure of two bivalve species, Ruditapes decussatus and Loripes lacteus to polymetallic pollution gradient, originating from harbor activities (Port-Camargue, south of France). Both bivalves differ by their trophic status, filter and deposit feeder for Ruditapes and symbiotic for Loripes that underlies potential differences in metal sensibility. The bivalves were immerged in July (for Ruditapes during 2 and 8 days) and in August 2012 (for Loripes during 2, 6 and 8 days) in the water column of the harbor, at 3 stations according to pollution gradient. Metal concentrations (Cu, Mn, Zn) in the water column were quantified as dissolved metals (measured by ICP-MS) and as labile metals (measured by ICP-MS using DGT technique). For each exposure time, accumulation of metals in the soft tissue of bivalves ("bioaccumulation") was measured for both species. In addition, specific parameters, according to the trophic status of each bivalve, were investigated: filtering activity (specific clearance rate, SCR) for Ruditapes, and relative cell size (SSC) and genomic content (FL1) of bacterial symbionts hosted in the gills of Loripes. The SCR of Ruditapes drops from 100% (control) to 34.7% after 2 days of exposure in the less contaminated site (station 8). On the other hand, the relative cell size (SSC) and genomic content (FL1), measured by flow cytometry were not impacted by the pollution gradient. Bioaccumulation was compared for both species, showing a greater capability of Cu accumulation for Loripes without lethal effect. Mn, Fe and Zn were generally not accumulated by any of the species according to the pollution gradient. The trophic status of each species may greatly influence their respective responses to polymetallic pollution.

Occurrence of an anthropogenic gadolinium anomaly in river and coastal waters of southern France.

This study reports a pronounced positive Gd anomaly in a small river and in the largest French Mediterranean lagoon. Along the studied catchment, this anomaly is also present in the effluents of the municipal sewage treatment plants, suggesting an anthropogenic origin for the Gd excess. The anomaly corresponds to a distinct increase of Gd concentrations (up to 19 pmol/l) in the river and around 5.4 pmol/l in the lagoon. The excess flux of Gd is compatible with the medical use of water soluble Gd complexes as contrasting agent in magnetic resonance imaging.

Bacterial immobilization and oxidation of arsenic in acid mine drainage (Carnoulès creek, France).

The acid waters (pH=2.73-3.37) originating from the Carnoulès mine tailings contain high dissolved concentrations of arsenic (1-3.5 mmol l(-1)) and iron (20-40 mmol l(-1)). At the outlet, arsenite predominates. During the first 30 m of downflow, 20-60% is removed by coprecipitation with Fe(III). This process results from bacterially mediated As- and Fe-oxidation. The precipitation rates in the creek depend on the oxygen concentration in spring water and are lower during the dry summer period when the anoxic character of the spring water inhibits the activity of oxidizing bacteria. Ex situ experiments show that the presence of bacteria-rich precipitates increases the As- and Fe-removal rates. Three strains of bacteria promoting the oxidation of As have been isolated, and two of them have the characteristics of Thiomonas ynys1. The third strain, which is not identified yet, also catalyzes the oxidation of Fe.

Arsenic oxidation and bioaccumulation by the acidophilic protozoan, Euglena mutabilis, in acid mine drainage (Carnoulès, France).

In the acid stream (pH 2.5-4.7) originating from the Carnoulès mine tailings, the acidophilic protozoan Euglena mutabilis grows with extremely high sulfate (1.9-4.9 g/l), iron (0.7-1.7 g/l) and arsenic concentrations (0.08-0.26 g/l). Strong variations in flow rate and high sulfate concentrations (up to 4.9 g/l) have been registered in early winter and might be the reason for the reduction in cell number of the protozoan from October to December 2001. No relation was established between arsenic concentration and/or speciation and abundance of the protozoan in the stream. Arsenite, which is the most toxic form, predominates in water. The oxidation of arsenite to arsenate occurred within a few days in laboratory experiments when E. mutabilis was present in Reigous Creek water and synthetic As(III)-rich culture medium. Methylated compounds (MMA, DMA) were not identified in the culture media. The protozoan bioaccumulated As in the cell (336 +/- 112 microg As/g dry wt.) as inorganic arsenite (105 +/- 52 microg As/g dry wt.) and arsenate (231 +/- 112 microg As/g dry wt.). Adsorption of As at the cell surface reached 57 mg/g dry wt. in the As(V) form for E. mutabilis grown in 250 mg/l As(III) synthetic medium. Both intracellular accumulation and adsorption at the cell surface increased for increasing As(III) concentration in the medium but the concentration factor in the cell relative to soluble As decreased.

Persisting impact of historical mining activity to metal (Pb, Zn, Cd, Tl, Hg) and metalloid (As, Sb) enrichment in sediments of the Gardon River, Southern France.

In this study, we assessed past and present influence of ancient mining activity on metal(loid) enrichment in sediments of a former mining watershed (Gardon River, SE France), that is now industrialized and urbanized. A sedimentary archive and current sediments were characterized combining geochemical analyses, zinc isotopic analyses and sequential extractions. The archive was used to establish local geochemical background and recorded (i) increasing enrichment factors (EFs) for Pb, Zn, Cd, Tl, Hg, As and Sb throughout the industrial era, (ii) a contamination peak in 1976 attributed to a tailings dam failure, and (iii) current levels in 2002 and 2011 similar to those of 1969, except for Sb and Hg, reflecting a persisting contamination pattern. Inter-element relationships and spatial distribution of EF values of current sediments throughout the watershed suggested that both ancient and current contamination had a common origin for Pb, Zn, Cd, Tl and As related to the exploitation of Pb/Zn mineralization while old Sb mines and coal extraction area were the main sources for Sb and Hg respectively. This prevailing mining origin was reflected for Zn by a relatively uniform isotopic composition at δ(66)Zn=0.23 ± 0.03‰, although slight decrease from 0.23‰ to 0.18‰ was recorded from upstream to downstream sites along the river course in relation with the contribution of the lighter δ(66)Zn signature (~0.08‰) of acid mine drainage impacted tributaries. Results from sequential extractions revealed that the potential mobility of the studied metal(loid)s varied in the order Sb

Diversity and spatiotemporal dynamics of bacterial communities: physicochemical and other drivers along an acid mine drainage.

Deciphering the biotic and abiotic factors that control microbial community structure over time and along an environmental gradient is a pivotal question in microbial ecology. Carnoulès mine (France), which is characterized by acid waters and very high concentrations of arsenic, iron, and sulfate, provides an excellent opportunity to study these factors along the pollution gradient of Reigous Creek. To this end, biodiversity and spatiotemporal distribution of bacterial communities were characterized using T-RFLP fingerprinting and high-throughput sequencing. Patterns of spatial and temporal variations in bacterial community composition linked to changes in the physicochemical conditions suggested that species-sorting processes were at work in the acid mine drainage. Arsenic, temperature, and sulfate appeared to be the most important factors that drove the composition of bacterial communities along this continuum. Time series investigation along the pollution gradient also highlighted habitat specialization for some major members of the community (Acidithiobacillus and Thiomonas), dispersal for Acidithiobacillus, and evidence of extinction/re-thriving processes for Gallionella. Finally, pyrosequencing revealed a broader phylogenetic range of taxa than previous clone library-based diversity. Overall, our findings suggest that in addition to environmental filtering processes, additional forces (dispersal, birth/death events) could operate in AMD community.

Diversity and geochemical structuring of bacterial communities along a salinity gradient in a carbonate aquifer subject to seawater intrusion.

In aquifers subject to saline water intrusion, the mixing zone between freshwater and saltwater displays strong physico-chemical gradients. Although the microbial component of these specific environments has been largely disregarded, the contribution of micro-organisms to biogeochemical reactions impacting water geochemistry has previously been conjectured. The objective of this study was to characterize and compare bacterial community diversity and composition along a vertical saline gradient in a carbonate coastal aquifer using high throughput sequencing of 16S rRNA genes. At different depths of the mixing zone, stable geochemical and hydrological conditions were associated with autochthonous bacterial communities harboring clearly distinct structures. Diversity pattern did not follow the salinity gradient, although multivariate analysis indicated that salinity was one of the major drivers of bacterial community composition, with organic carbon, pH and CO2 partial pressure. Correlation analyses between the relative abundance of bacterial taxa and geochemical parameters suggested that rare taxa may contribute to biogeochemical processes taking place at the interface between freshwater and saltwater. Bacterial respiration or alternative metabolisms such as sulfide oxidation or organic acids production may be responsible for the acidification and the resulting induced calcite dissolution observed at a specific depth of the mixing zone.

Three-year survey of sulfate-reducing bacteria community structure in Carnoulès acid mine drainage (France), highly contaminated by arsenic.

A 3-year survey on sulfate-reducing bacteria (SRB) was conducted in the waters of the arsenic-rich acid mine drainage (AMD) located at Carnoulès (France) to determine the influence of environmental parameters on their community structure. The source (S5 station) exhibited most extreme conditions with pH lowering to ~1.2; iron, sulfate, and arsenic concentrations reaching 6843, 29 593, and 638 mg L(-1), respectively. The conditions were less extreme at the downstream stations S1 (pH ~3.7; iron, sulfate, and arsenic concentrations of 1114, 4207, and 167 mg L(-1), respectively) and COWG (pH ~3.4; iron, sulfate, and arsenic concentrations of 854, 3134, and 110 mg L(-1), respectively). SRB community structures were characterized by terminal restriction fragment length polymorphism and library analyses based on dsrAB genes. The predominant dsrAB sequences detected were most similar to the family Desulfobulbaceae. Additionally, certain phylotypes could be related to spatio-temporal fluctuations of pH, iron, and arsenic species. For example, Desulfohalobiaceae-related sequences were detected at the most acidic sample (pH 1.4) with high iron and arsenic concentrations (6379 and 524 mg L(-1), respectively). New dsrAB sequences, with no isolated representatives, were found exclusively in COWG. This study gives new insights on SRB community dynamics in AMD systems.