Bioaccessibility, solid phase distribution, and speciation of Sb in soils and in digestive fluids

Abstract : Antimony (Sb) is a pollutant found in lead-contaminated soils and occurs mainly in oxidation states Sb(III) or Sb(V), this latter being the less toxic forms to organisms. In human health risk assessment, soil ingestion is one of a major exposure route in which Human bioavailability is not considered. The objectives of this paper were to establish a link between Sb speciation in soils and its bioaccessibility considering the possible evolution of the speciation in the digestive tract. Four soils were sampled around a former lead-extraction site. Total Sb content on these soils ranged between 26 mg kg-1 and 1150 mg kg-1. Sb bioaccessibility in the soils was measured using an in vitro Bioaccessibility Group Research Europe (BARGE) digestion test. A sequential extraction procedure and physical analyses were carried out on these samples to estimate Sb speciation in soils. Differential pulse anodic stripping voltammetry (DPASV) was also used to study the evolution of Sb speciation during the digestion process. For the four samples, Sb bioaccessibility was low, ranging between 1.5% and 12% of total Sb content. Sequential extractions and physical analysis on the most contaminated soil showed that Sb was mostly occurring in the iron oxide and sulphide phases and in the pentavalent form. No change of this speciation was occurring during the digestion process. Determination of the Sb speciation in the soil matrix is thus an accurate way to demonstrate that this metalloïd can be considered as a non major issue in the overall risk characterisation if it occurs under the pentavalent form.