Stability of arsenic species in hydroponic media and its influence on arsenic uptake and distribution in White mustard (Sinapis alba L.)

The long-term uptake and distribution of arsenic compounds by hydroponically cultivated White mustard (Sinapis alba) was investigated with a special emphasis on controlling the stability of the arsenic compounds in nutrient solution during the experiment. It was concluded that arsenites are rapidly oxidised to arsenates during the 7-day cultivation of White mustard. The presence of plant roots increases the oxidation rate of arsenites. Dimethylarsinic acid (DMA) and arsenates remain stable during the exposition, while monomethylarsonic acid (MMA) is partially demethylated. When the nutrient solution containing arsenites is exchanged daily, the distribution of arsenic in White mustard is significantly different (translocation factor-TF-is 70 times higher) in comparison to the experiment without exchange of the medium. Speciation analysis of arsenic in plant tissues and in nutrient solutions was performed by high performance liquid chromatography with inductively coupled plasma-mass spectrometry (HPLC ICP-MS). The results obtained unquestionably illustrated that the uncontrolled conditions of hydroponic plant cultivation may be a source of misinterpretation of all the obtained data. Additionally, the synthesis of phytochelatins in plants exposed to different arsenic compounds was investigated. Phytochelatins were identified in tissues of plants exposed to arsenites and arsenates, and their presence was correlated with high arsenite content. Phytochelatin synthesis was not indicated in plants grown in the presence of MMA and DMA.