Accumulation of selenium in natural plants and selenium supplemented vegetable and selenium speciation by HPLC-ICPMS

Abstract

Samples of different grass types, white clover, red clover, dandelion, English plantain, different sorts of vegetables, such as garlic, radish and carrot, with the associated soil samples were collected at sites located 300 to 600 meters away from the coal-fired thermal power plant Šoštanj in the Šalek valley in Slovenia. In the soil the highest soil average selenium concentration (1.21 mg Se kg-1) was obtained at the margin of a coal ash dump whereas at other locations the selenium soil concentrations varied between 0.87 and 0.98 mg Se kg-1. Among collected plants the lowest selenium accumulation was obtained in dried grass samples (~ 80μg Se kg-1) and in the edible parts of the vegetable (10-50μg Se kg-1).In a separate experiment, cabbage, radish, onion and garlic growing outdoors in beds with an area of 1.6m2and 0.8 m2 were supplemented with selenium twice between the growing period by foliar aspiration with an aqueous solution of sodium selenate until 10 mg Se m-2 and 20 mg Se m-2 were added.Radish was harvested after 17 days, and garlic, onion and cabbage one and half months after the last selenium supplementation. Most of the accumulated selenium was present in the vegetative parts of vegetable, and after the addition of 20mg Se m-2 the highest selenium concentration was determined in onion and radish leaves (37.4 and 37.1 mg kg-1) followed by leaves of garlic (19.6 mg kg-1) and cabbage (11.9mg kg-1). In the edible parts, selenium accumulation increased with increasing selenium supplementation, and after addition of 20mg Se m-2 the highest selenium accumulation was obtained in cabbage (~ 12 mg kg-1)followed by radish (8.2mg kg-1), garlic (6.6mg kg-1) and onion (5.6mg kg-1). After extraction with methanol/water solution (9: 1) selenium compounds were determined in the extracts by HPLC- ICPMS by application of an anion-exchange PRP- χ 100 chromatographic column with 10 mM citric acid solution at pH 5.0 as mobile phase. The obtained extraction efficiencies were between 20 and 30% with the maximum value for radish and the minimum value for cabbage.In the extracts of radish, about 100% of the extracted selenium was selenate. In the extract of garlic, besides selenate and traces of selenite, selenomethionine was also determined. In the extracts of cabbage and onions, about 90% of the extracted selenium was present as selenate.