Assessment of Cadmium and Zinc Contamination in the Soils Around Pha Te Village, Mae Sot District, Tak Province, Thailand

Abstract

In this study sequential extraction was used to fractionate cadmium (Cd) and zinc (Zn) from soils into six operationally defined groups; water soluble, buffer-exchangeable, carbonate, FeMn oxide, organic, and residual. Soil samples from agricultural areas surrounding Pha Te village, Mae Sot District, Tak Province, Thailand, were classified into four categories; forest soil, upland soil, upper-paddy soil and lower-paddy soil. Total soil Cd and Zn concentrations ranged from 0.63 to 30.4 mg kg^-1 and 14.4 to 594 mg kg^-1, respectively. Cd and Zn concentrations were higher in the upper- and lower-paddy soil (5.93 to 30.4 mg kg^-1 for Cd and 286 to 594 mg kg^-1 for Zn). These soils are considered as polluted. Cd in the polluted soil was dominantly associated with the buffer-exchangeable and carbonate-bound (40 to 70 % of total Cd), while in non-polluted soils; the residual fraction was dominant (50 to 80 % of the total Cd). The major proportion of Zn (37 to 46 % of total Zn) in the non-polluted soil and the upper-paddy soil occurred in the residual fraction. On the other hand, the major proportion of total Zn in the lower-paddy soil was associated with FeMn oxides (36 % of total Zn). The results show that mobility and potential bioavailability of Cd and Zn (61 and 25 %) in polluted soil were higher than in non-polluted soils (15 and 19 % in Cd and Zn, respectively). Metal distribution in different chemical fractions in these soils depended on the respective total metal concentrations.