Garcia Salgado, Sara y Quijano Nieto, M. Angeles
Levels of toxic arsenic species in native terrestrial plants from soils polluted by former mining activities.
En: "1st International Conference on Pollutant Toxic Ions and Molecules (PTIM 2015)", 2-4 de noviembre de 2015, Caparica (Portugal). ISBN 978-989-99361-6-4. pp. 146-147.
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 safe