Levels of toxic arsenic species in native terrestrial plants from soils polluted by former mining activities

Arsenic is considered a toxic element for plants. However, the discovery of arsenic resistant and hyperaccumulating plant species has increased the interest in understanding the distribution of arsenic species in these environmental matrices. Although As can be present in plants under different chemical forms, such phytochelatins, the As remained in plants as free inorganic or methylated ions has a greater interest due to its higher mobility and toxicity, and therefore, its ecological impact and risk to health. The aim of this work consisted on the determination of the fraction of As present as toxic forms (inorganic and methylated species) present in native terrestrial plants from polluted soils by former mining activities (Mónica mine, NW Madrid, Spain), with high total arsenic concentration levels (up to 3,500 µg g-1), due to their higher mobility and the risk associated to their reintegration into other environmental compartments. Roots and aboveground parts were analysed separately, to assess possible transformations from translocation processes. Extractions were carried out with deionized water by microwave-assisted extraction, at a temperature of 90 °C and three extraction steps of 7.5 min each. Total extracted arsenic concentrations were determined by ICP-AES, showing extraction percentages from 9 to 39%. Speciation studies were performed by HPLC-(UV)-HG-AFS, and they showed the main presence of As(V) (up to 350 µg g-1), followed by As(III), in both plant parts. Monomethylarsonic acid (MMA) and trimethylarsine oxide (TMAO) were also found only in some plants. On the other hand, the use of 0.5 mol L-1 acetic acid as extractant led to higher extraction percentages (33-87%), but lower column recoveries, probably due to the extraction of arsenic compounds different to toxic free ions studied, which may come from biotransformation mechanisms carried out by plants to reduce arsenic toxicity. However, As(V) concentrations increased up to 800 µg g-1 in acid medium, indicating the probable release of As(V) from organoarsenic compounds and therefore a higher potential risk for the environment. From the easily soluble, water-extractable arsenic species concentration levels, it can be drawn that between 70 and 89% of the total arsenic in plants must have been biotransformed, so it is present under the form of different arsenic compounds. Still, high As concentration levels remain as toxic forms, predominantly As(V), reaching up to 190 µg g-1 considering roots and aboveground parts separately, and 350 µg g-1 considering the sum of both plant parts (more than double in acid medium), which may constitute an environmental risk due to its possible reintegration to the environment. Therefore, the study and control of native plants growing in As polluted soils is a relevant factor for environmental saf

Toxic arsenic compounds remain in native plant species from arsenic polluted soils

Conferencia sobre fitorremediación de suelos contaminados con metales pesados y arsénico y estudios de especiación de arsénico en las plantas autóctonas acumuladoras

Single extraction tests for risk assessment of arsenic and heavy metals in polluted soils from mining activities

Se presentan los resultados obtenidos en la aplicación de 3 métodos de extracción simple, para evaluar el grado de movilidad y biodisponibilidad de As, Cd, Cu, Pb y Zn, en suelos afectados por la actividad minera. Los métodos desarollados están basados en el empleo de agentes extractantes de diferente naturaleza y UPS, con determinación por ICP-AES. El estudio estadístico de los resultados obtenidos, permitió establecer el método más adecuado en función del elemento analizado, debido a su diferente asociación a los componentes del suelo

Arsenic speciation in plants by HPLC-(UV)-HG-AFS: Optimisation of the extraction method and application to native plant species from soils polluted by mining activities

Se ha optimizado el método de extracción de especies de arsénico hidrosolubles en muestras de plantas terrestres procedentes de suelos contaminados por actividad minera. La especies extraídas se han determinado mediante HPLC-(UV)-HG-AFS

Application of ultrasound probe sonication for arsenic and heavy metal extraction in soils

Se ha optimizado un método de extracción de arsénico y metales pesados en suelos contaminados procedentes de actividad minera, mediante la aplicación de la sonda de ultrasonidos focalizada

Arsenic and heavy metal uptake and accumulation in native plant species from soils polluted by mining activities

Arsenic and heavy metal (specifically Cd, Cr, Cu, Ni, Pb, and Zn) uptake, translocation, and accumulation in ten native plant species spontaneously growing in soils polluted by mining activities were studied, with a focus on future phytoremediation work in polluted soils. Plant and soil samples were collected in the vicinity of the Mónica mine (NW Madrid, Spain). Soil analysis showed the ability of native plants for growing in soils with high concentration levels of Cd, Cu, Pb, Zn, and especially As. From these elements, the highest percentage of extractable elements was found for Cd and the lowest for Pb. A highly significant correlation was observed between total and extractable element concentrations in soils, except for Cu, indicating that total concentration is the most relevant factor for element mobility in these soils. Extractable elements in soils were better correlated with concentrations in plants than total elements in soils; thus, extraction methods applied are suitable to estimate the element phytoavailable fraction in soils, which depends on the plant species and not only on the element mobility in soils. High element concentrations were found in the aboveground parts of Corrigiola telephiifolia (As and Pb), Jasione montana (Cd and Zn), and Digitalis thapsi (As, Cd, Cu, Pb and Zn). However, considering the translocation and accumulation factors, together with the concentration levels found in roots and aboveground parts, only C. telephiifolia could be considered a Pb accumulator and an As hyperaccumulator plant, which could be used for future phytoremediation work in soils polluted with As

Determination of toxic arsenic species and arsenosugars in edible seaweed by HPLC-(UV)-HG-AFS

Arsenic is a toxic element widely distributed in the environment, and the estimation of its toxicity requires knowledge of the individual arsenic species present in biological materials. Marine algae contribute substantial amounts of arsenic to the human diet in Asian countries, and nowadays their popularity in western countries is increasing due to their high mineral content and their recognized therapeutic properties1. It is known that marine organisms can accumulate considerable arsenic concentrations, up to ug g"1 level, which may be harmful to human beings. In seaweed, the main arsenic species are usually arsenoribosides (arsenosugars), which are considered to be non-toxic to living organisms and can be present at trace levéis, so analysis techniques of high sensitivity are needed to carry out their determination

Determination of soluble toxic arsenic species in alga samples by microwave-assisted extraction and high performance liquid chromatography-hydride generation-inductively coupled plasma-atomic emission spectroscopy

A microwave-based procedure for arsenic species extraction in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) is described. Extraction time and temperature were tested in order to evaluate the extraction efficiency of the process. Arsenic compounds were extracted in 8 ml of deionised water at 90 °C for 5 min. The process was repeated three times. Soluble arsenic compounds extracted accounted for about 78–98% of total arsenic. The results were compared with those obtained in a previous work, where the extraction process was carried out by ultrasonic focussed probe for 30 s. Speciation studies were carried out by high performance liquid chromatography–hydride generation–inductively coupled plasma-atomic emission spectrometry (HPLC-HG-ICP-AES). The chromatographic method allowed us to separate As(III), As(V), monomethylarsonic acid and dimethylarsinic acid in less than 13 min. The chromatographic analysis of the samples allowed us to identify and quantify As(V) in Hizikia sample and Sargasso material, while the four arsenic species studied were found in Chlorella sample. In the case of Laminaria sample, none of these species was identified by HPLC-HG-ICP-AES. However, in the chromatographic analysis of this alga by HPLC-ICP-AES, an unknown arsenic species was detected

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic. An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed. Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min−1 flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g−1), Sargassum (38 ± 2 μg g−1) and Chlorella (9 ± 1 μg g−1) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g−1). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volum

Assessment of total arsenic and arsenic species stability in alga samples and their aqueous extracts

In order to achieve reliable information on speciation analysis, it is necessary to assess previously the species stability in the sample to analyse. Furthermore, in those cases where the sample treatment for species extraction is time-consuming, an assessment of the species integrity in the extracts is of paramount importance. Thus, the present paper reports total arsenic and arsenic species stability in alga samples (Sargassum fulvellum and Hizikia fusiformis), as well as in their aqueous extracts, which were stored in amber glass and polystyrene containers at different temperatures. Total arsenic determination was carried out by inductively coupled plasma atomic emission spectroscopy (ICP-AES), after sample acid digestion in a microwave oven, while arsenic speciation was conducted by anion exchange high performance liquid chromatography on-line coupled to ICPAES, with and without sample introduction by hydride generation (HPLC-ICP-AES and HPLC-HG-ICP-AES), after aqueous microwave-assisted extraction. The results obtained for solid alga samples showed that total arsenic (for Hijiki alga) and arsenic species present (As(V) for Hijiki and NIES No. 9 Sargasso) are stable for at least 12 months when samples are stored in polystyrene containers at +20 ◦C. On the other hand, a different behaviour was observed in the stability of total arsenic and As(V) species in aqueous extracts for both samples, being the best storage conditions for Sargasso extracts a temperature of −18 ◦C and polystyrene containers, under which they are stable for at least 15 days, while Hijiki extracts must be stored in polystyrene containers at +4 ◦C in order to ensure the stability for 10 days