Bioaccessibility of Organochlorine Pesticides in Contaminated Soil: A Poultry-Informed In Vitro Gastrointestinal Model

Free-ranging poultry ingest 4–30 g of soil per day, making soil a significant route of organochlorine pesticide (OCP) exposure in agricultural areas with legacy contamination. However, total soil concentrations overestimate actual exposure. Only the bioaccessible fraction, mobilized within the gastrointestinal tract, governs transfer to eggs and meat. Static physiologically based extraction test (PBET) models consistently underestimate this fraction for hydrophobic compounds due to re-equilibration of desorbed contaminants onto the soil matrix. This study applied and evaluated a sink-modified static in vitro gastrointestinal model incorporating Tenax resin as a sorption sink to assess OCP bioaccessibility in spiked aged soil under simulated poultry digestive conditions. The aqueous phase-only fraction (gastric plus intestinal liquid) ranged from 0.004 to 17.1%, while the aqueous phase plus sorption sink (Tenax) fraction, measured from the same intestinal phase incubation, ranged from 24.0 to 52.7%, with the largest relative changes observed for HCH isomers (from near-undetectable levels without Tenax) and 2.7- to 4.3-fold increases for DDT-related compounds, a difference confirmed as statistically significant (paired t-test) for six of the seven compounds. One-way ANOVA revealed significant differences among compounds (F(6,21) = 5.53, p = 0.0014). Tukey’s HSD showed that β-HCH (56.1 ± 10.6%) and 4,4′-DDT (55.6 ± 24.0%) had significantly higher bioaccessibility than γ-HCH (25.8 ± 0.9%), 2,4′-DDD (22.2 ± 18.0%), and 4,4′-DDE (22.0 ± 5.7%), while α-HCH (28.6 ± 3.9%) and 4,4′-DDD (33.9 ± 8.1%) occupied an intermediate position, not significantly different from either group. A substantial fraction of mobilized OCPs was associated with the Tenax sink (17–53%), confirming that aqueous phase measurements alone underestimate the bioaccessible pool. These results demonstrate the importance of including a sorption sink in poultry-informed gastrointestinal models for accurate assessment of OCP transfer from contaminated soil to food products.