Soil ingestion can be a major route of human exposure to many immobile soil contaminants. The present risk assessment is based on toxicity studies in which contaminants are typically ingested in liquid or food matrices. The difference in bioavailability of contaminants ingested in a soil matrix is not taken into account. To become bioavailable, contaminants first need to become bioaccessible, i.e., they must be mobilized from the soil during digestion. Soil contaminants may be less bioaccessible than contaminants from liquid or food, so that the risks can be overestimated. This article describes the development of an in vitro human digestion model that is physiologically based. It can be used as a tool to assess bioaccessibility. We explain the rationale behind the experimental design of the model. We address the aspects of the simulated compartments of the gastrointestinal tract, temperature, soil-to-fluid ratio, ratio of digestive juices, transit times, centrifugation, pH values, mixing, constituents and their concentrations, and bile. The optimized in vitro digestion model was applied in a case study. The bioaccessibility of lead in pottery flakes with glazing was determined and compared to the bioaccessibility of lead in the soil from which the pottery flakes were removed. The data indicate that pottery flake lead is considerably less bioaccessible (0.3 +/- 0.2%) than lead in soil without pottery flakes (42-66% at the same site, and 28-73% at other sites in the same town). Furthermore, bioaccessibility values of lead in soil appear to be less than calculated bioaccessibility values for dietary lead (which are based on the criterion used by the Dutch risk assessment and on literature absorption data). This indicates that accounting for the matrix of ingestion can affect the exposure assessment for lead. The in vitro digestion model is a promising tool for studying the effect of the ingestion matrix on bioaccessibility.

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In April 2019 a proficiency test for mycotoxins in oat meal was organised by Wageningen Food Safety Research (WFSR), Wageningen University & Research in accordance with ISO 17043. WFSR, part of Wageningen University & Research is accredited for the organisation of proficiency tests in the field of contaminants, pesticides, mycotoxins, plant toxins and veterinary drugs in feed and feed ingredients according to ISO/IEC 17043 (R013). The primary goal of this proficiency test was to give participants the opportunity to evaluate or demonstrate their competence for the analysis of mycotoxins in oat meal. Two materials were prepared and dispatched on dry-ice to the participants. The consensus values of the mycotoxins in each material are given in Table 1. Table 1 Consensus values of the mycotoxins in the proficiency materials.

Matrix: A= Rye, B= Mix wheat/oat (1:1) 1) robust relative standard deviation (interlaboratory RSD based on participants' results).2) calculated using a fit-for-purpose target RSD for proficiency of 25%. False negatives were counted here as unsatisfactory z-score.3) the number and percentage here means: analyte determined, method with a sufficiently low LOQ to allow quantification, and obtaining a satisfactory z-score. Results: Material A (rye) Material A Ergocornine A: 53.2 µg/kg u: 1.56 µg/kg σp: 13.3 µg/kg (25%) robust σ: 7.18 µg/kg (14%) Ergocorninine A: 40.9 µg/kg u: 1.73 µg/kg σp: 10.2 µg/kg (25%) robust σ: 7.69 µg/kg (19%) Ergocristine A: 82.7 µg/kg u: 3.29 µg/kg σp: 20.7 µg/kg (25%) robust σ: 14.9 µg/kg (18%) Ergocristinine A: 50.4 µg/kg u: 2.78 µg/kg σp: 12.6 µg/kg (25%) robust σ: 12.8 µg/kg (25%) Lab code Result (µg/kg) z-score Result (µg/kg) z-score Result (µg/kg) z-score Result (µg/kg) z-score Material A Ergosine A: 81.9 µg/kg u: 2.75 µg/kg σp: 20.5 µg/kg (25%) robust σ: 12.5 µg/kg (15%) Ergosinine A: 46.0 µg/kg u: 2.58 µg/kg σp: 11.5 µg/kg (25%) robust σ: 11.5 µg/kg (25%) Ergotamine A: 126 µg/kg u: 5.66 µg/kg σp: 31.5 µg/kg (25%)robust σ: 25.2 µg/kg (20%) Ergotaminine A: 65.3 µg/kg u: 3.20 µg/kg σp: 16.3 µg/kg (25%) robust σ: 14.3 µg/kg (22%) Total sum A: 701 µg/kg u: 24.0 µg/kg σp: 175 µg/kg (25%) robust σ: 110 µg/kg (16%) Result (µg/kg) z-score Result (µg/kg) z-score Result (µg/kg) z-score Result (µg/kg) z-score Result (µg/kg) z-score

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