Dynamic sequential extraction procedure using a four-channel circulating flow system for extracting Hg from soil samples.

Mercury (Hg) is harmful to the human body. Its physical properties and toxicity differ greatly depending on its chemical form. The quantification of soluble Hg in soils or sediments is crucial for preventing further environmental contamination by Hg sources such as products, processes, and storage. In this study, the risk of leachable Hg that release from soil to the hydrosphere was evaluated by the sequential extraction procedure (SEP), a speciation method of a targeted element based on the solubility of its various compounds. The SEP, which consists of a four-channel circulating flow system (FCFS), was developed to reduce the time and amount of liquid required for SEP of leachable Hg in the Bloom method, which is a conventional SEP for Hg in a solid sample. The SEP with FCFS was optimized by considering the impact of extractant volume, circulation extraction time, and flushing of the extraction line. In the three-step (Fraction 1-3) sequential extraction of leachable Hg in soil samples, the optimized SEP with FCFS required 45 mL of extractant and 2.5 h, while the common batch SEP required 75 mL of extractant and 49 h. Furthermore, the combination of the SEP with FCFS for the leachable forms (Fraction 1-3) and the batch method for the insoluble forms (Fraction 4-5) was applied to the five-step SEP of Hg from CRM-JSAC0403. The sum of Hg concentrations that were classified into five fractions was in good agreement with that obtained from the batch method for all extraction, indicating that there are no significant differences in the concentrations extracted from the four channels.