Assessment of oral bioaccessibility of organochlorine pesticides in soil using an in vitro gastrointestinal model.

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.