Phytoremediation of Thallium Contaminated Soils by Brassicaceae

Abstract

In order to assess the efficacy of phytoremediation, the thallium (Tl)-hyperaccumulator plants kale, Brassica oleracea acephala L. cv. Winterbor F1, and candytuft, Iberis intermedia Guers., were grown in several Tl-contaminated soils. These soils differed in their total Tl concentration (1.4 to 153 mg Tl kg⁻¹ soil), the origin of pollution (anthropogenic vs. geogenic), as well as Tl binding forms, which were characterized by a sequential extraction. In soils with geogenic Tl the percentage of easily accessible fractions was relatively low amounting to 5% of total Tl. In contrast, in soils with anthropogenic Tl pollution the pool of easily accessible Tl was large amounting to 23% of total Tl in the soil polluted by deposition from cement plant. As a consequence, the partition ratio of shoot Tl concentration vs. total soil Tl concentration ranged from 1 to 12 for soils contaminated by geogenic and anthropogenic sources, respectively. In general, there was no relationship between Tl uptake by the hyperaccumulator plants and the total Tl concentration of the soils. The plant uptake of Tl depended on the capacity of the soils to replenish the soil solution with Tl as well as the replenishment from less accessible binding forms.