Uptake of thallium from artificially contaminated soils by kale (Brassica oleracea L., var. acephala)

Abstract

A pot experiment focused on the study of factors influencing thallium transfer from contaminated soils into kale (green cabbage, Brassica oleracea L. var. acephala, variety Winterbor F1) was evaluated. Three different types of topsoils with naturally low content of thallium (heavy, medium and medium-light soil) were used for pot experiments. The soils were contaminated with thallium sulfate to achieve five levels of contamination (0, 0.52, 2.10, 4.20 and 5.88 mg/kg). There were six replicates for each combination (90 pots in the experiment). The first part of the experiment started in the year of contamination (2001) and continued in 2003. The soil samples and the samples of kale (leaves and stalks were sampled separately) were collected and analysed. Kale was found to be able to accumulate Tl without any influence on yield. The highest thallium concentration was found in the leaves of kale in the first year of the experiment and reached 326 mg/kg dry matter. Bioaccumulation factor (Biological Absorption Coefficient -BAC) was found to be over 80 during the first year of the experiment. In the third year the BAC was around 3 for the soil with the highest pH and the highest organic matter content but as high as 15 for an acid soil with the lowest content of organic matter and the lowest Cation Exchange Capacity (CEC) of soils. The content of thallium in the leaves of kale was found to be 7 to 10 times higher than in the stalks in the third year. In the first year this ratio was up to 18. From these findings it can be concluded that the ability of some plants of Brassicacea family, that are planted as common vegetables, to accumulate thallium is very high and can be a serious danger for food chains. Neutral soils high in CEC and organic matter are able to bind thallium more effectively than poor acid soils and the transfer of Tl into plants from these soils is substantially lower. The uptake of Tl from contaminated soils into kale can be very high and without any negative effect on the plant growth. The transfer of Tl into kale decreases with the time necessary to reach the equilibrium between the added Tl and the soil (ageing of a sample).

Standards for the contents of heavy metals and metalloids in soils

“…It is regarded to be a very dangerous metal [44,45], more dangerous than mercury [51]. This is proved by its lower MPA value-0.25 and 1.9 mg/kg for thallium and mercury, respectively-although there is no MPC/APC for Tl in soils.…”

“…Its ionic radius is close to that of K + ; as a result, Tl + replaces potassium in metabolism processes. Thallium is very mobile in soils; its availability for plants depends on its total content in the soil and on the form of its compounds [44,45]. The content of Tl in plants usually reaches (and often even exceeds) half of its total content in the soil [44,45].…”

“…Thallium is very mobile in soils; its availability for plants depends on its total content in the soil and on the form of its compounds [44,45]. The content of Tl in plants usually reaches (and often even exceeds) half of its total content in the soil [44,45]. The coefficient of the bio logical consumption of Tl reaches 80 in acidic soils with a low content of organic matter.…”

Thallium uptake by white mustard (Sinapis alba L.) grown on moderately contaminated soils—Agro-environmental implications

“…The phytoavailability of Tl depends on plant species, its form of binding and content of Tl in soil [7]. Previous investigations found that Brassicaceae plants have a potential to accumulate elevated amounts of Tl [6,8,9].…”

Indirect Speciation Analysis of Thallium in Plant Extracts by Anodic Stripping Voltammetry

“…Some of these plants, especially species belonging to the Brassicaceae family – Armoracia rusticana 12, Sinapis alba 13 and Iberis intermedia 7 – are able to accumulate extremely high amounts of thallium in their tissues. This ability, characterized by accumulation and translocation factors, was also observed for plants grown hydroponically 14, and in soil spiked with TlCl 15 and Tl 2 SO 4 solutions 16. Studies on thallium speciation indicated that its dominating form in plant tissues is monovalent thallium 7,14,15, but Sinapis alba cultivated in solid medium in the presence of high thallium concentrations additionally contained Tl(III) species 17.…”