Bioaccessibility And Bioavailability Of OCPs And PAHs In Food Using An In-vitro Gastrointestinal Model

A static in-vitro gastrointestinal model was used to investigate the oral bioaccessibility and bioavailability of OCPs and PAHs in contaminated different foods and soils with different organic matter contents. A key hypothesis to be tested is that the sorption of a fraction of OCPs and PAHs mobilized from soil into the digestive fluid on the solid phase leads to underestimation of the digestion coefficients.It was demonstrated that there were significant influence of the sorption on the results and the underestimation can be corrected by a multiple fluid/soil ratios experimental design.The finally determined bioaccessibilities of various OCP compounds varied from only 4% (α-HCH in soil B) to 97% (o,p'-DDD in soil A). On average of the four soil samples, the bioaccessibilities of HCHs and DDTs were 21% and 50%, respectively, compared to 13% and 42% without sorption correction. For the total PAHs, the digestion coefficients were 97.7±6.6%,63.7±0.8%,42.9±4.2%,8.46±0.4% for the four soil samples with various organic carbon contents, respectively.Among the OCP contaminants studied,α-HCH are chiral. Although technical HCHs contains the (+)- and (-)-α-HCH enantiomers in a 1:1 racemic mixture, non-racemic residues were sometime detected in environmental media including soil and ambient air primarily due to enantioselective microbial degradation. In this study, however, the mean and standard deviation of EF for the four soils sampled were 0.503±0.020, showing a racemic mixture of the (+)- and (-)-α-HCH enantiomers. During the in-vitro digestion, the enantiomeric compositions deviated significantly from racemic, showing a clear signal for bioactivity of the chiralα-HCH, likely because of the stereochemical selectivity of enzymes involved. After the gastric digestion, (+)-α-HCH in both fractions increased significantly (p < 0.01) for the liquid and solid fractions, respectively. After the intestinal digestive process, enantiomeric composition returned to near racemic for the liquid and solid fractions. It seems that (+)-α-HCH was mobilized faster than (-)-α-HCH during gastric digestion while (-)-α-HCH was mobilized faster than (+)-α-HCH during intestinal digestion. Although the enantiomeric compositionα-HCH eventually returned to racemic, the enantiomeric excess of (+)-α-HCH during the digestion process may result in preferential absorption of (+)-α-HCH by small intestine.The bioaccessibility of HCHs in crucian and lettuce is 92%,29%, respectively, DDTs is 70%,94%,respectively. We examined the uptake rates of contaminants using intestinal epithelial Caco-2 cells. The uptake rates of HCHs and DDTs were range from 30% to 80% and from 50% to 70%, respectively.