Evaluation of Extractants for Estimation of Tl Availability to Barley and Sunflower Grown in Tl-Contaminated Soils

Abstract

Thallium (Tl) is a highly toxic heavy metal that poses a threat to various organisms, including human beings. In plants, Tl is mostly present as the uncomplexed Tl+ species, and its uptake by plants follows a similar trend to that of other monovalent ions such as NH4+, Cs+, K+, Rb+, and others. In this study, we investigated the relationships between the Tl concentrations in barley and sunflower and the extractable-Tl concentrations in acidic, neutral, and alkaline soils. We used ammonium and potassium based-inorganic salt extractants, including 1 M NH4Cl, 1 M (NH4)2SO4, 1 M KCl, and 1 M KNO3. The Tl concentration in the sunflower tissues harvested from the acidic soil with a treatment of 40 mg Tl kg-1 was 1,910 mg kg-1, indicating that sunflower could be considered a Tl-hyperaccumulator plant. Among the extractants, the highest concentration of extractable soil Tl was obtained using 1 M NH4Cl solution, followed by 1 M (NH4)2SO4, 1 M KCl, and 1 M KNO3. The Tl concentrations in both plants were well related (R2 > 0.910) to the Tl concentrations extractable by ammonium and potassium-based inorganic salts and showed the closest relationship (R2 = 0.936 - 0.980) with that extractable by 1 M (NH4)2SO4. Therefore, the ammonium and potassium based-inorganic chemicals can be considered applicable soil Tl extractants in relation to Tl uptake by plants.The coefficient of determination (R2) values between the Tl concentrations in the plants and the chemical extractable-soil Tl concentrations. Plant Extractant Coefficient of determination (R2) JJ† IS DY Barley 1 M NH4Cl 0.914 0.917 0.961 1 M (NH4)2SO4 0.962 0.936 0.963 1 M KCl 0.935 0.910 0.948 1 M KNO3 0.923 0.918 0.948 Sunflower 1 M NH4Cl 0.945 0.981 0.973 1 M (NH4)2SO4 0.980 0.958 0.980 1 M KCl 0.965 0.981 0.977 1 M KNO3 0.946 0.973 0.984 †JJ, acidic Jeonju soil; IS, neutral Iksan soil; DY, alkaline Danyang soil.