Assessment of Oral Bioaccessibility of Organochlorine Pesticides in Soil Using an In Vitro Gastrointestinal Model

Abstract

A static in vitro gastrointestinal model was used to investigate the oral bioaccessibility of organochlorine pesticides (OCPs) including hexachlorocyclohexane isomers (HCHs) and dichlorodiphenyltrichloroethane and metabolites in contaminated soils with different organic matter contents. A key hypothesis tested was that a fraction of the mobilized contaminants is sorbed on the solid after digestion, and this fraction could be desorbed and become bioaccessible in the intestinal tract due to absorption of the dissolved fraction by the small intestine. The bioaccessibility would be underestimated if the sorbed fraction was separated from the fluid by centrifugation or filtration in an in vitro test. In our experiment, a procedure using multiple fluid-to-solid ratios was developed to characterize the sorption. It was found that 8-38% of the mobilized OCPs were sorbed on the residue and remained in the solid phase after the separation. Taking into consideration the sorbed fraction, the measured bioaccessibilities of the OCPs varied from 4% to 97% depending on the properties of the soils and the compounds. The enantiomeric ratios of chiral compounds studied were also determined to distinguish biotic (enzymatic) and abiotic (chemical extraction) processes in the in vitro digestion model. It was found that although alpha-HCH in the raw soils was racemic, (+)-alpha-HCH was enriched in the gastric digestive fluid but depleted in the intestinal digestive fluid.

Assessment of the Bioaccessibility of Polybrominated Diphenyl Ethers in Foods and the Correlations of the Bioaccessibility with Nutrient Contents

“…This observation was consistent with the above speculation, i.e., PBDEs accumulated in the fat during digestion. Similar correlations were reported between K OW and the bioaccessibility of organochlorine pesticides in soil samples (29). However, it was different for the foods with low fat content (chicken, 6.6%, and pork, 5.0%) in which the bioaccessibility of individual PBDE congeners in a given food was virtually independent of their lipophilicity ( Figure 2B).…”

‘Towards a unified approach for the determination of the bioaccessibility of organic pollutants’

“…Tao et al (2009) reported bioaccessibility values between 4% and 97% through in vitro testing of OCP contaminated soils. Differences in soil properties, particularly organic content, and the physicochemical properties of the analytes were cited as reasons for variation within the test.…”

“…Under the current regulation oral exposure is determined as total pesticide extracted from the plant material, typically using solvent based extraction methods from which a maximum residue level is determined (OECD, 2013). This is problematic as it has been demonstrated that the proposed bioaccessible concentrations of pesticides are often higher using solvent extraction methods than synthetic gastrointestinal extractions (Tao et al, 2009).…”

Mobilization of Soil-Bound Residue of Organochlorine Pesticides and Polycyclic Aromatic Hydrocarbons in an in vitro Gastrointestinal Model

“…In one of our previous studies, mobilities of OCPs in soils were investigated using an in-vitro gastrointestinal model (19). It was noticed that the total quantity of α- HCH measured in the supernate and pellet after the digestion was higher than that measured in the raw samples using solvent extraction.…”

“…It was noticed that the total quantity of α- HCH measured in the supernate and pellet after the digestion was higher than that measured in the raw samples using solvent extraction. It was thus suspected that a part of bound residue of α-HCH in the soil, which was not extractable even by a solvent extraction, was mobilized during the in-vitro digestion (19). If this hypothesis is true, and the phenomenon is common, some sequestrated pollutants in soil or other matrix such as food can be mobilized and become bioaccessible in the gastrointestinal tract.…”