Arsenic immobilization and transformation by biofilms developed over riverbed sediments

Biofilms are complex communities of autotrophic and heterotrophic organisms immersed in a matrix mainly composed by polysaccharides. They are ubiquitous over wet surfaces and provide protection for microorganisms. In river environments there is evidence that biofilms play an important role in the biogeochemical cycles of nutrients and contaminants. The objective of this work is to evaluate the effect of the fluvial epipsammic biofilm on the retention and transformation of As and to understand its interaction with this metalloid in the Anllóns River (Galicia, NW Spain), where As pollution has been observed. The results revealed that biofilms play a key role in As biogeochemistry in freshwater environments, favouring As immobilization, especially in environments where As and P occur simultaneously, and promoting As detoxification by inhibiting the reduction of AsV to AsIII and methylating inorganic As

Arsenic Transfer from As-Rich Sediments to River Water in the Presence of Biofilms

The influence of epipsammic biofilms on As release from river sediments was evaluated in a microcosm experiment where biofilms were grown on sediments containing 106 mg kg−1 As, collected in the Anllóns River, and compared with control systems without biofilms. The As transfer to the water column was low (<0.11% of total As in the sediment) and was further reduced by 64% in the presence of biofilms. was the predominant species in the overlying water in both systems. concentration was higher (up to 12% of total dissolved As) in the control systems than in the systems with biofilms, where this species was almost absent. This fact is of toxicological relevance due to the usually higher mobility and toxicity of the reduced species. Control systems exhibited higher As mobility in water, in sulphate solution, and in weak acid medium and higher bioavailability in diffusive gradient in thin films (DGT) devices. Arsenic retained by the biofilm was equally distributed between extracellular and intracellular compartments. Inside the cells, significant concentrations of , monomethylarsonic acid (), and dimethylarsinic acid () were detected, suggesting that active methylation (detoxification) processes are occurring in the intracellular compartmentThe authors wish to thank the Spanish Ministry of Economy and Competitiveness (MINECO-FEDER) for financial support (Projects Ref. CGL2010-22059 and CGL2013-46003-P). Diego Martiñá Prieto wishes to acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness for his FPI Fellowship (BES-2011-044514)S

Estudo a escala de microcosmos de barreiras reativas permeáveis com serragem de granito e composto para o tratamento de água contaminadas com Cr (VI)

The permeable reactive barrier (PRB) is a technology developed for the removal of contaminants in groundwater. It consists of a screen perpendicular to the flow of contaminated groundwater filled with a material capable of adsorbing, precipitating or degrading pollutants. Several materials have been tested for their use as reactive substrates for the construction of PRBs. Waste materials are of particular interest for this purpose due to the possibility of their reuse and their generally lower cost. With this aim, the Cr (VI) retention capacity of filler material consisting either of pine bark compost (PB) or a 50% mixture of compost and granite powder (PB50) was evaluated using an experimental device specifically designed for this study, which reproduces a permeable reactive barrier at the laboratory scale. Percolation experiments were carried out with a solution of 100 mg L-1 Cr (VI) in 0.01M KNO3, followed by a leaching step with the saline background. The results show that compost is a highly efficient filler for permeable reactive barriers with almost 100% retention of Cr, whereas the retention efficiency of the mixture of PB50 oscillated between 18 and 46% during the experiment. The Cr retained by the filling material is strongly fixed, since no desorption was detected by leaching with the saline background, and concentrations in the standard Toxic Characteristic Leaching Procedure (TCLP) extracts were lower than 1 mg L-1. This behaviour minimizes the risk of release of the Cr retained by the material of the barrier in the event of it being traversed by water not contaminated with Cr. Modelling with Visual Minteq indicates that in the experiments with PB, the reduction of Cr (VI) to Cr (III) occurs and that Cr (III) is associated with dissolved organic matter, which is a form of lower toxicity than the initial Cr (VI) species. In turn, in the experiments with PB50, Cr (III) and Cr (VI) coexist and the oxidised form is not associated with dissolved organic matter, which suggests greater toxicity. The results indicate that pine bark compost is a potential candidate for use as filler material permeable reactive barriers.Las barreras permeables reactivas (BPRs) son tecnologías de eliminación de contaminantes en aguas subterráneas, que consisten en una pantalla perpendicular al flujo de agua subterránea contaminada, rellena de un material con capacidad de adsorber, precipitar o degradar los contaminantes. Se han evaluado diversos materiales reactivos como material de relleno de BPRs, siendo de especial interés la utilización de materiales residuales, por la posibilidad de su reutilización y, frecuentemente, menor coste. Con este fin se estudió la capacidad de retención de Cr (VI) de compost de corteza de pino (PB) y de una mezcla al 50% de compost y serrines graníticos (PB50), utilizando un dispositivo diseñado específicamente para este estudio, que reproduce una barrera permeable reactiva a escala de laboratorio. Para evaluar la retención se llevó a cabo un experimento de percolación con una disolución de 100 mg L-1 de Cr (VI) en KNO3 0,01M, seguido de una etapa de lavado con el fondo salino, para evaluar la liberación del Cr previamente retenido. Los resultados mostraron una gran eficacia del compost como material de relleno de BPRs, consiguiendo una retención de Cr cercana al 100%. La mezcla de serrín granítico y compost presentó una capacidad de retención que osciló entre el 18 y el 46% a lo largo del experimento. El Cr retenido por el material de relleno se encuentra fuertemente fijado, pues no se desorbe por lixiviación con la solución salina y las concentraciones en los extractos obtenidos mediante la aplicación del procedimiento estándar de lixiviación Toxic Characteristic Leaching Procedure (TCLP) fueron inferiores 1 mg L-1. Este comportamiento minimiza el riesgo de liberación del Cr retenido por el material de la barrera, en el supuesto de que fuera atravesada por un agua no contaminada con Cr. La modelización con Visual Minteq indica que, en los eluatos de los experimento con PB, se ha producido reducción de Cr (VI) a Cr (III), y éste se encuentra asociado con la materia orgánica disuelta, lo que sugiere una reducción de la toxicidad en comparación con la que presenta el Cr (VI) introducido en la solución de percolación. En los eluatos del experimento con PB50 se encuentran tanto Cr (III) como Cr (VI), y la forma oxidada no se encuentra asociada con la materia orgánica disuelta. Los resultados de este estudio indican que el compost de corteza de pino tiene un gran potencial para ser usado como material de relleno de barreras permeables reactivas.Entre as tecnologias desenvolvidas para a remoção de contaminantes em águas subterrâneas são as barreiras permeáveis reactivas (BPRs), as quais consistem de uma trincheira perpendicular ao fluxo das águas subterrâneas contaminadas, cheia com um material capaz de adsorver, precipitar ou degradar poluentes. Diversos matérias foram ensaiados como substratos reativos na construção de BPRs, sendo de interesse a utilização de materiais residuais, pela possibilidade de reutilização e, geralmente, menor custo. Para este fim foi avaliada a capacidade de retenção de Cr (VI) de um composto de casca de pinheiro (PB) ou uma mistura de 50% de composto e pó de serragem de granito (PB50), usando um dispositivo experimental que simula uma barreira permeável reactiva a escala de laboratorio. Experiências de percolação foram levadas a cabo com uma solução de 100 mg L-1 de Cr (VI) em 0,01MKNO3, seguida por um passo de lavagem com a solução salina. Os resultados obtidos mostram uma alta eficáciado composto, com uma retenção de 100% de Cr. A eficiência de retenção da mistura de serradura de grantito e de composto oscilou entre 18-46% ao longo do experimento. O Cr é fortemente retido pelo material de enchimento, não dessorvido por lixiviação com a solução salina, enquanto que as concentrações dos extractos obtidos pela aplicação do procedimento de lixiviação standar Toxic Characteristic Leaching Procedure (TCLP) eram inferiores a 1 mg L-1. Este comportamento reduz o risco de a liberação da carga de Cr retida pelo BPR o que poderia acontecer se águas limpas passan através da barreira. O modelado com Visual Minteq indica que nas experiências com PB ocorre redução de Cr (VI) a Cr (III), e que o Cr (III) está associado com a matéria orgânica dissolvida, que é uma forma de toxicidade mais baixa do que as espécies de Cr (VI) iniciais, enquanto nas experiências com PB50, Cr (III) e Cr (VI) coexistem, e o Cr (VI) não está associado com a matéria orgânica dissolvida, o que sugere uma maior toxicidade. Os resultados indicam que o composto de casca de pinheiro é um candidato potencial para utilização como material de enchimento de barreiras permeáveis reactivas.The study was funded by the Xunta de Galicia through the project entitled Avaliación do uso de materiais de caracter inerte e orgánico para o tratamento de augas contaminadas –Tradesol (09MDS005CT). The authors also thank Xunta Galicia-Feder for the financial support through "Axudas de Consolidación e Estruturación de Unidades de Investigación Competitivas. IN845B-2010/038 and GRC2014/028". Diego Martiñá Prieto wishes to acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness for his FPI Fellowship (BES-2011-044514)S

Mutual interaction between arsenic and biofilm in a mining impacted river

Gold mining activities in fluvial systems may cause arsenic (As) pollution, as is the case at the Anllóns River (Galicia, NW Spain), where high concentrations of arsenate (AsV) in surface sediments (up to 270 mg kg−1) were found. A 51 day-long biofilm-translocation experiment was performed in this river, moving some biofilm-colonized substrata from upstream (less As-polluted) to downstream the mine area (more As-polluted site), to explore the effect of As on benthic biofilms, as well as their role on As retention and speciation in the water-sediment interface. Eutrophic conditions (range: 0.07–0.38 mg L−1 total phosphorus, TP) were detected in water in both sites, while sediments were not considered P-polluted (below 600 mg kg−1). Dimethylarsenate (DMAV) was found intracellularly and in the river water, suggesting a detoxification process by biofilms. Since most As in sediments and water was AsV, the high amount of arsenite (AsIII) detected extracellularly may also confirm AsV reduction by biofilms. Furthermore, translocated biofilms accumulated more As and showed higher potential toxicity (higher As/P ratio). In concordance, their growth was reduced to half that observed in those non-translocated, became less nutritive (less nitrogen content), and with higher bacterial and dead diatom densities. Besides the high As exposure, other environmental conditions such as the higher riparian cover at the more As-polluted site could contribute to those effects. Our study provides new arguments to understand the contribution of microorganisms to the As biogeochemistry in freshwater environmentsThis work was supported by the Spanish Ministry of Economy and Competitiveness (Project Ref. CGL2010-22059, CGL2013-46003-P and CGL2013-43822-R), the University of Girona (Project Ref. SING12/09 and MPCUdG2016/120) and the Government of Catalonia (Project Ref. 2014 SGR 484). Laura Barral Fraga benefited from a doctoral fellowship from the University of Girona (BR 2013/06) and a mobility grant from the Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA, at Bordeaux, France)S

Lixiviação de Al e Fe em solos sumetidos a queimadas controladas em laboratório

The influence of the severity of soil heating on aluminium and iron leaching was analysed, as well as its relationship with the solubility of organic matter. For this purpose, laboratory experiments were carried out under microcosm conditions where unaltered soil blocks were submitted to thermal shock and subsequently to rainfall simulation (300 mm), collecting the surface (0 cm) and subsurface runoff (12 cm). Soil heating was carried out using infrared lamps reaching temperatures of 222 and 401 ºC at a depth of 1 cm, similar to those reached in moderate and high intensity fires respectively. The analysis of the drainage waters showed that the leaching of Al increased with the severity of the thermal shock, whereas for Fe perceptible effects were only seen at the highest temperature. Geochemical modelling with Visual MINTEQ indicated that Al and Fe were fundamentally mobilised and associated with dissolved organic matter. Weak interactions (electrostatic binding) predominated in the case of Al and strong interactions (bidentate complexes with dissolved organic matter) in the case of Fe. Only towards the end of the leaching experiment, when the concentration of dissolved organic carbon decreased, was there a perceptible mobility of Al and Fe in the inorganic form, in the subsurface leachate of the moderate temperature treatment.Se analizó la in!uencia de la severidad del calentamiento del suelo en la lixiviación de aluminio y hierro, y su relación con la solubilidad de la materia orgánica. Para tal fin, se realizaron experimentos de laboratorio, en condiciones de microcosmos, en los que bloques de suelo inalterados fueron sometidos a choques térmicos y posteriormente a la acción de lluvia simulada (300 mm), recogiendo las aguas de escorrentía superficial (0 cm) y subsuperficial (12 cm). El calentamiento del suelo se llevó a cabo por medio de lámparas infrarrojas, que permitieron alcanzar temperaturas de 222 y 401 ºC, a 1 cm de profundidad, similares a las que se alcanzan, respectivamente, en incendios de severidad moderada y alta. El análisis de los lixiviados mostró que el lavado de Al aumentó con la severidad del choque térmico, mientras que para el Fe solo se observaron efectos apreciables para la temperatura más alta. La modelización geoquímica con el programa Visual Minteq indicó que Al y Fe se movilizaron fundamentalmente asociados a materia orgánica disuelta, redominando las uniones débiles (enlace electrostático) en el caso del Al y las uniones fuertes (complejos bidentados con la materia orgánica disuelta) en el caso del Fe. Únicamente hacia el final del experimento de lixiviación, cuando disminuyó la concentración de carbono orgánico disuelto, se observó una movilización apreciable de Al y Fe en forma inorgánica en el lavado subsuperficial del tratamiento de moderada temperatura.Analisou-se a influência da severidade do aquecimento do solo na lixiviação do alumínio e do ferro, bem como a sua relação com a solubilidade da matéria orgânica. Assim, realizaram-se ensaios laboratoriais desenvolvidos em microcosmos, com blocos de solo não alterados submetidos a choques térmicos e seguidamente a testes de chuva simulada (300 mm). Recolheram-se as águas de escorrimento superficial (0 cm) e subsuperficial (12 cm). O aquecimento do solo foi feito com lâmpadas de infravermelho atingindo temperaturas de 222 e 401 ºC a 1 cm de profundidade, à semelhança das alcançadas em incêndios forestais de média e alta intensidade. A análise dos lixiviados mostrou que a lixiviação do Al aumenta com a severidade do choque térmico, enquanto que no caso do ferro apenas foram percetíveis efeitos para a temperatura mais elevada A modelagem geoquímica com o programa Visual Minteq, indicou que o Al e o Fe sofrem mobilização em associação com a matéria orgânica dissolvida, com o predomínio de interações fracas (ligação eletrostática) no caso do Al e de interações fortes (complexos bidentados com matéria orgânica dissolvida) no caso do Fe. Apenas no fim do ensaio de lixiviação, quando as concentrações carbono orgânico dissolvido diminuem, ocorre mobilização apreciável de Al e Fe na forma inorgânica no lixiviado subsuperficial do tratamento da temperatura média.S

Assessment of the Chronic Toxicity and Interactions between Arsenic and Riverbed Biofilms

The toxic effect of exposure to arsenic, As(V), at concentrations of 0 to 30 mg L&minus;1, for 49 days, on epipsammic biofilms, was evaluated in a microcosm experiment. The growth and composition of biofilms developed on sediments containing As concentrations of 31 mg kg&minus;1 and 85 mg kg&minus;1 were compared, using photosynthetic parameters and Live/Dead stains as end points. A toxic effect of arsenic could not be demonstrated; however, biofilm growth was higher over the sediment with higher arsenic concentrations, suggesting the development of pollution-induced community induced tolerance (PICT). Nevertheless, PICT was not observed after exposure to high arsenic concentration in the laboratory, as there were no differences in algal growth between the previous 0 and 30 mg L&minus;1 systems exposed to new 30 mg As L&minus;1 dissolution over 29 days. The algal composition was affected by the added arsenic, and brown algae were the most tolerant compared to green algae and cyanophyceae, as their percentage increased from 25 and 33% in the control samples to 57 and 47% in the samples with the highest added As concentration. In turn, the biofilm development influenced arsenic redistribution and speciation. Arsenic concentration in water decreased with time during the incubation experiment, retained by the sediment particles and the biofilm. In the biofilm, extracellular As was significantly higher (up to 11 times) than intracellular arsenic. As(V) was the predominant species in water and in the biofilm, but products of biotic transformation, namely As(III), DMA(V) and MMA(V), were also found in the solution and in the biofilm in some systems, demonstrating reduction and methylation by the organisms. As a conclusion, a toxic effect was not detected for the concentrations evaluated. Biofilms naturally exposed in the river system to high As concentrations acquire pollution-induced tolerance; however, tolerance was not acquired by exposure to 30 mg L&minus;1 for 29 days in the laboratory

Arsenic Mobility in As-Containing Soils from Geogenic Origin: Fractionation and Leachability

The lithogenic arsenic in soils of the Anllóns River basin (Spain) was quantified, its chemical fractions were determined, and its leachability characteristics were compared under various experimental conditions. Fifty soil samples of C horizons, sampling an area of 50 km2 along the river course, were submitted to an exploratory analysis. Pseudo-total arsenic ranged between 2 and 489 mg kg−1. Arsenic leachability using the standard methods DIN 38414-S4 and TCLP was less than 0.25% of pseudo-total As. Then the effect of pH (3, 6, and 9), solid : liquid (S : L) ratio (1 : 10 and 1 : 50), phosphate (10 mM), and contact time (24 and 240 h) on arsenic mobilization was studied in nine soils with the highest As concentration. Arsenic mobilization increased at alkaline pH and lower S : L ratio; the most decisive factor was the addition of phosphate, increasing arsenic leachability up to 1,000 times, and this increased even 2.3 times when the contact time was extended from 24 hours to 240 hours. The results suggest that the mobilization of arsenic may be underestimated in short-term water leaching tests and that the environmental conditions favouring arsenic mobilization should be taken into account for a sound evaluation of the transfer risk of arsenic towards aquatic ecosystems

A microcosm study of permeable reactive barriers filled with granite powder and compost for the treatment of water contaminated with Cr (VI)

The permeable reactive barrier (PRB) is a technology developed for the removal of contaminants in groundwater. It consists of a screen perpendicular to the flow of contaminated groundwater filled with a material capable of adsorbing, precipitating or degrading pollutants. Several materials have been tested for their use as reactive substrates for the construction of PRBs. Waste materials are of particular interest for this purpose due to the possibility of their reuse and their generally lower cost. With this aim, the Cr (VI) retention capacity of filler material consisting either of pine bark compost (PB) or a 50% mixture of compost and granite powder (PB50) was evaluated using an experimental device specifically designed for this study, which reproduces a permeable reactive barrier at the laboratory scale. Percolation experiments were carried out with a solution of 100 mg L-1 Cr (VI) in 0.01M KNO3, followed by a leaching step with the saline background. The results show that compost is a highly efficient filler for permeable reactive barriers with almost 100% retention of Cr, whereas the retention efficiency of the mixture of PB50 oscillated between 18 and 46% during the experiment. The Cr retained by the filling material is strongly fixed, since no desorption was detected by leaching with the saline background, and concentrations in the standard Toxic Characteristic Leaching Procedure (TCLP) extracts were lower than 1 mg L-1. This behaviour minimizes the risk of release of the Cr retained by the material of the barrier in the event of it being traversed by water not contaminated with Cr. Modelling with Visual Minteq indicates that in the experiments with PB, the reduction of Cr (VI) to Cr (III) occurs and that Cr (III) is associated with dissolved organic matter, which is a form of lower toxicity than the initial Cr (VI) species. In turn, in the experiments with PB50, Cr (III) and Cr (VI) coexist and the oxidised form is not associated with dissolved organic matter, which suggests greater toxicity. The results indicate that pine bark compost is a potential candidate for use as filler material permeable reactive barriers.Entre as tecnologias desenvolvidas para a remoção de contaminantes em águas subterrâneas são as barreiras permeáveis reactivas (BPRs), as quais consistem de uma trincheira perpendicular ao fluxo das águas subterrâneas contaminadas, cheia com um material capaz de adsorver, precipitar ou degradar poluentes. Diversos matérias foram ensaiados como substratos reativos na construção de BPRs, sendo de interesse a utilização de materiais residuais, pela possibilidade de reutilização e, geralmente, menor custo. Para este fim foi avaliada a capacidade de retenção de Cr (VI) de um composto de casca de pinheiro (PB) ou uma mistura de 50% de composto e pó de serragem de granito (PB50), usando um dispositivo experimental que simula uma barreira permeável reactiva a escala de laboratorio. Experiências de percolação foram levadas a cabo com uma solução de 100 mg L-1 de Cr (VI) em 0,01M KNO3, seguida por um passo de lavagem com a solução salina. Os resultados obtidos mostram uma alta eficácia do composto, com uma retenção de 100% de Cr. A eficiência de retenção da mistura de serradura de grantito e de composto oscilou entre 18-46% ao longo do experimento. O Cr é fortemente retido pelo material de enchimento, não dessorvido por lixiviação com a solução salina, enquanto que as concentrações dos extractos obtidos pela aplicação do procedimento de lixiviação standar Toxic Characteristic Leaching Procedure (TCLP) eram inferiores a 1 mg L-1. Este comportamento reduz o risco de a liberação da carga de Cr retida pelo PRB, o que poderia acontecer se águas limpas passan através da barreira. O modelado com Visual Minteq indica que nas experiências com PB ocorre redução de Cr (VI) a Cr (III), e que o Cr (III) está associado com a matéria orgânica dissolvida, que é uma forma de toxicidade mais baixa do que as espécies de Cr (VI) iniciais, enquanto nas experiências com PB50, Cr (III) e Cr (VI) coexistem, e o Cr (VI) não está associado com a matéria orgânica dissolvida, o que sugere uma maior toxicidade. Os resultados indicam que o composto de casca de pinheiro é um candidato potencial para utilização como material de enchimento de barreiras permeáveis reactivas.Las barreras permeables reactivas (BPRs) son tecnologías de eliminación de contaminantes en aguas subterráneas, que consisten en una pantalla perpendicular al flujo de agua subterránea contaminada, rellena de un material con capacidad de adsorber, precipitar o degradar los contaminantes. Se han evaluado diversos materiales reactivos como material de relleno de BPRs, siendo de especial interés la utilización de materiales residuales, por la posibilidad de su reutilización y, frecuentemente, menor coste. Con este fin se estudió la capacidad de retención de Cr (VI) de compost de corteza de pino (PB) y de una mezcla al 50 % de compost y serrines graníticos (PB50), utilizando un dispositivo diseñado específicamente para este estudio, que reproduce una barrera permeable reactiva a escala de laboratorio. Para evaluar la retención se llevó a cabo un experimento de percolación con una disolución de 100 mg L-1 de Cr (VI) en KNO3 0,01M,  seguido de una etapa de lavado con el fondo salino, para evaluar la liberación del Cr previamente retenido.  Los resultados mostraron una gran eficacia del compost como material de relleno de BPRs, consiguiendo una retención de Cr cercana al 100%. La mezcla de serrín granítico y compost presentó una capacidad de retención que osciló entre el 18 y el 46% a lo largo del experimento. El Cr retenido por el material de relleno se encuentra fuertemente fijado, pues no se desorbe por lixiviación con la solución salina y las concentraciones en los extractos obtenidos mediante la aplicación del procedimiento estándar de lixiviación Toxic Characteristic Leaching Procedure (TCLP) fueron inferiores 1 mg L-1. Este comportamiento minimiza el riesgo de  liberación del Cr retenido por el material de la barrera, en el supuesto de que fuera atravesada por un agua no contaminada con Cr. La modelización con Visual Minteq indica que, en los eluatos de los experimento con PB, se ha producido reducción de Cr (VI) a Cr (III), y éste se encuentra asociado con la materia orgánica disuelta, lo que sugiere una reducción de la toxicidad en comparación con la que presenta el Cr (VI) introducido en la solución de percolación. En los eluatos del experimento con PB50 se encuentran tanto Cr (III) como Cr (VI), y la forma oxidada no se encuentra asociada con la materia orgánica disuelta. Los resultados de este estudio indican que el compost de corteza de pino tiene un gran potencial para ser usado como material de relleno de barreras permeables reactivas

Mutual interaction between Arsenic and biofilm in a mining impacted river

Gold mining activities in fluvial systems may cause arsenic (As) pollution, as is the case at the Anllóns River (Galicia, NW Spain), where high concentrations of arsenate (AsV) in surface sediments (up to 270 mg kg−1) were found. A 51 day-long biofilm-translocation experiment was performed in this river, moving some biofilm-colonized substrata from upstream (less As-polluted) to downstream the mine area (more As-polluted site), to explore the effect of As on benthic biofilms, as well as their role on As retention and speciation in the water-sediment interface. Eutrophic conditions (range: 0.07-0.38 mg L−1 total phosphorus, TP) were detected in water in both sites, while sediments were not considered P-polluted (below 600 mg kg−1). Dimethylarsenate (DMAV) was found intracellularly and in the river water, suggesting a detoxification process by biofilms. Since most As in sediments and water was AsV, the high amount of arsenite (AsIII) detected extracellularly may also confirm AsV reduction by biofilms. Furthermore, translocated biofilms accumulated more As and showed higher potential toxicity (higher As/P ratio). In concordance, their growth was reduced to half that observed in those non-translocated, became less nutritive (less nitrogen content), and with higher bacterial and dead diatom densities. Besides the high As exposure, other environmental conditions such as the higher riparian cover at the more As-polluted site could contribute to those effects. Our study provides new arguments to understand the contribution of microorganisms to the As biogeochemistry in freshwater environment

Biotic and Abiotic Factors Influencing Arsenic Biogeochemistry and Toxicity in Fluvial Ecosystems: A Review

Este artículo contiene 28 páginas, 6 figuras, 1 tabla.This review is focused on the biogeochemistry of arsenic in freshwaters and, especially, on the key role that benthic microalgae and prokaryotic communities from biofilms play together in through speciation, distribution, and cycling. These microorganisms incorporate the dominant iAs (inorganic arsenic) form and may transform it to other arsenic forms through metabolic or detoxifying processes. These transformations have a big impact on the environmental behavior of arsenic because different chemical forms exhibit differences in mobility and toxicity. Moreover, exposure to toxicants may alter the physiology and structure of biofilms, leading to changes in ecosystem function and trophic relations. In this review we also explain how microorganisms (i.e., biofilms) can influence the effects of arsenic exposure on other key constituents of aquatic ecosystems such as fish. At the end, we present two real cases of fluvial systems with different origins of arsenic exposure (natural vs. anthropogenic) that have improved our comprehension of arsenic biogeochemistry and toxicity in freshwaters, the Pampean streams (Argentina) and the Anllóns River (Galicia, Spain). We finish with a briefly discussion of what we consider as future research needs on this topic. This work especially contributes to the general understanding of biofilms influencing arsenic biogeochemistry and highlights the strong impact of nutrient availability on arsenic toxicity for freshwater (micro) organisms.This research was funded by the Spanish Ministry of Economy and Competitiveness (MINECO-FEDER) (ProjectRef. CGL2010-22059,CGL2013-46003-P,andCGL2013-43822-R),the program“Ayudas de Consolidación e Estructuración de Unidades de Investigación Competitivas”(ProjectRef. GRC2014/028) from the Xunta de Galicia, also the Generalitat de Catalunya (ref. 2017 SGR 548), and the University of Girona (Project Ref. SING12/09 and MPCUdG2016/120). Laura Barral Fraga benefited from a doctoral fellowship from the University of Girona (BR 2013/06) and a mobility grant from the Institut national de recherche en sciences et technologies pour l’environnement et l’agriculture (IRSTEA) at Bordeaux, France.Peer reviewe