In vivo validation of the unified BARGE method to assess the bioaccessibility of arsenic, antimony, cadmium, and lead in soils.

The relative bioavailability of arsenic, antimony, cadmium, and lead for the ingestion pathway was measured in 16 soils contaminated by either smelting or mining activities using a juvenile swine model. The soils contained 18 to 25,000 mg kg(-1) As, 18 to 60,000 mg kg(-1) Sb, 20 to 184 mg kg(-1) Cd, and 1460 to 40,214 mg kg(-1) Pb. The bioavailability in the soils was measured in kidney, liver, bone, and urine relative to soluble salts of the four elements. The variety of soil types, the total concentrations of the elements, and the range of bioavailabilities found were considered to be suitable for calibrating the in vitro Unified BARGE bioaccessibility method. The bioaccessibility test has been developed by the BioAccessibility Research Group of Europe (BARGE) and is known as the Unified BARGE Method (UBM). The study looked at four end points from the in vivo measurements and two compartments in the in vitro study ("stomach" and "stomach and intestine"). Using benchmark criteria for assessing the "fitness for purpose" of the UBM bioaccessibility data to act as an analogue for bioavailability in risk assessment, the study shows that the UBM met criteria on repeatability (median relative standard deviation value <10%) and the regression statistics (slope 0.8 to 1.2 and r-square > 0.6) for As, Cd, and Pb. The data suggest a small bias in the UBM relative bioaccessibility of As and Pb compared to the relative bioavailability measurements of 3% and 5% respectively. Sb did not meet the criteria due to the small range of bioaccessibility values found in the samples.

Modelling Pb bioaccessibility in soils contaminated by mining and smelting activities.

This investigation was undertaken to identify the most significant parameters that can be used to model the bioaccessibility of lead in contaminated soils. Twenty-five soil samples contaminated by two distinct sources of contamination (mining and smelting areas) were investigated in this work. Edaphic soil properties were determined using the classic techniques. Speciation and solid phase distribution of Pb were determined by sequential fractionation and physical analysis (XRD and SEM-EDX). Bioaccessibility of Pb was measured using the unified BARGE protocol on each soil samples and each residue following the different steps of the sequential extraction procedure. Results showed that Pb speciation varied according to the source of contamination. Pb gastric bioaccessibility ranged from 12% to 86% in mining soils and from 40% to 95% in smelting soils. Soil edaphic properties (pH, CEC, clays content or organic matter content) cannot be used to model Pb bioaccessibility as these parameters could not be extrapolated from on site to another. The differences in Pb bioaccessibility between the 25 soils were better reflected by the nature of the Pb-bearing minerals as characterized by sequential extractions. Soluble, exchangeable and acid-soluble phases could explain from 70 to 98% of Pb bioaccessibility. Consequently, Pb bioaccessibility is extremely sensitive to the Pb-bearing phase distribution. This distribution should be thoroughly evaluated before applying any remedial techniques that would potentially affect Pb speciation in soils.

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

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 26mgkg(-1) and 1150mgkg(-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.

Bioaccessibility of lead in high carbonate soils.

Metal bioaccessibility is not currently considered in the French human health risk assessment procedure. For contaminants such as Pb this parameter could have a significant effect on the risk calculation. From the literature, it seems that Pb bioaccessibility is strongly controlled by the occurrence of cerrussite in soils: with a high cerussite content showing a positive correlation with high Pb bioaccessibility. Assuming this hypothesis, Pb contained in carbonated soils could show strong human bioaccessibility. This study aims to examine the link between high carbonate soil minerals, focussing particularly on cerrussite and the Pb bioaccessibility. Four soils were sampled in a high carbonate area in France contaminated with Pb due to mining activities. Pb bioaccessibility was measured using the in vitro RIVM protocol. In parallel, the solid phase Pb distribution was determined using chemical sequential extraction for each sample and physical analysis on the more contaminated sample. Results showed that Pb bioaccessibility was significantly different among soil samples. As shown in literature, cerussite (PbCO3) was a highly bioaccessible phase and 40% of Pb in the waste material was present in this form. However, cerussite alone did not account for all of the Pb which was also present in highly stable minerals containing sulphur. Pb associated to these minerals is also likely to be significantly bioaccessible. Indeed, sequential extraction showed that most of the Pb was associated with the sulphur-compartment. This study shows that Pb bioaccessibility in high carbonate soils can be low (down to 20% of the total soil Pb content) and is not correlated with cerussite soil contents even if the concentration of this mineral is relatively high. Consequently, risk management of Pb contamination should not focus only on high carbonate soils but also on Pb contained in other minerals which is also likely to be significantly bioaccessible.