Overview and challenges of mercury fractionation and speciation in soils

Analytical procedures to assess mercury speciation in soils still lack consensus. This article presents an overview of the mercury fractionation and speciation procedures used in soils. Mercury fractionation is the most common approach despite the operational definition of the fractions. Application of single extraction procedures that target the water-soluble, exchangeable and acid-soluble fractions and the application of EPA method 3200 for mercury sequential extraction are examined in soils with different physicochemical characteristics. A step forward in mercury speciation is thermo-desorption, a useful tool to rapidly obtain needed information about contaminated soils. The advantages and limitations of these procedures are compared; the importance of soils' physicochemical characteristics highlighted. Criteria to be considered when choosing a suitable method are given - assessing total mercury concentration, soil physicochemical characteristics, environmental conditions, and legislation. It is recommended that the interpretation of results is done wisely, to correctly support decisions concerning intervention strategies at contaminated sites.