Development of an In Vitro Digestion Model for Estimating the Bioaccessibility of Soil Contaminants

Abstract

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.

Effect of the diet amended with risk elements contaminated soil on risk elements content in tissues and hematological parameters of rats

“…For the evaluation of bioaccessible portions of elements in soils and experimental diets the PBET test (Ruby et al, 1996;Oomen et al, 2003) was applied in two phases as follows:…”

The relationship between soil geochemistry and the bioaccessibility of trace elements in playground soil

“…The RIVM (Rijksinstituut voor Volksgezondheid en Milieu, Dutch Institute for Public Health and the Environment) method (Oomen et al 2003) which simulates the digestive process in mouth, stomach and intestine: 9 mL of artificial saliva was added to 0.6 g of soil in centrifuge tubes and the mixture rotated for 5 min at 37 °C. Subsequently, 13.5 ml of gastric juice was added and the mixture rotated for 4 h at 37 °C.…”

“…0.9 ml of chyme was diluted with 8.1 ml of HN0 3 2 % for analysis. Details of the composition of artificial saliva, gastric juice and intestinal juices are presented in Oomen et al (2003).…”

“…Ruby et al 1999) rather than methods seeking to replicate complete mouth-gastric-intestinal pathways (e.g. Oomen et al 2003). The present paper follows on from the earlier work of Mingot et al (2011), utilising both the two simplified standard protocols they used to evaluate trace element gastric bioaccessibility and the one which mimics the mouth-gastric-intestinal digestion pathway.…”

Laboratory efforts to cultivate noroviruses

“…Artificial intestinal juices were produced as described by Oomen et al (2003). Human small intestinal contents were obtained from the duodenum of a patient with an ileostomy and were provided by D. Graham at Baylor College of Medicine (Houston, TX, USA).…”