Comparison of sequential extraction methods with reference to zinc fractions in contaminated soils

The total amount of zinc extracted from soils in the Legnicko–Głogowski Copper Mining Region using either the McLaren and Crawford or Tessier et al. method differed within the limits of 2–35%, while the application of the latter method yielded higher results for 86% of analyzed samples. Amongst zinc fractions analyzed using the McLaren and Crawford method the fraction of zinc specifically bound and less easily exchangeable dominates in horizons where there is an accumulation of organic matter while in the remaining horizons a residual fraction. Whereas when the Tessier et al. method was used the residual fraction dominated in all the genetic horizons of soils under study. The smallest amounts of zinc, regardless of the method applied, were found in the fraction embracing ions found in the soil solution and those easily exchangeable. The quantity of mobile zinc (accessible for plants) calculated on the basis of sequential extraction according to McLaren and Crawford procedure amounts to up to 14–54% while the quantity obtained by the Tessier et al. method amounts to up to 6–28% of total zinc value. A significant difference was found in accumulation horizons and amounted to 40-54% and 8-28% respectively. The share of organic substance in zinc binding was smallest when assessed on the basis of sequential analysis according to McLaren and Crawford. While in the case of applying the method by Tessier et al. the smallest amounts of zinc were bound to carbonates, sulphates and phosphates.