Toluene and methyl tert butyl ether bioaccessibility in soils: The influence of their coexistence

Toluene (TOL) and methyl tert butyl ether (MTBE), significant components of gasoline, are common contaminants found in soils at petrochemical sites. Oral bioaccessibility is a crucial parameter for accurate human health risk assessment; however, the influence of the coexistence of TOL and MTBE on their bioaccessibility remains unclear. Therefore, in this study, soil samples co-contaminated with TOL and MTBE were collected from a petrochemical site to investigate the impact of their coexistence on bioaccessibility by using an in vitro gastrointestinal model. The results demonstrated that the oral bioaccessibility of TOL ranged from 51.74 % to 71.90 %, while that of MTBE ranged from 76.33 % to 83.07 %. Furthermore, the presence of MTBE significantly (p < 0.05) increased the bioaccessibility of TOL in both the gastric and small intestinal phases. These findings indicated a potential risk associated with oral exposure. The hydroxypropyl- β -cyclodextrin (HPCD) and dichloromethane-acetone (DCM/Ace) fractions of TOL and MTBE were predominant in both the gastric and small intestinal phases. The presence of MTBE significantly reduced ( p < 0.05) the equilibrium absorption capacity ( q e ) of TOL, which decreased from 353.9 mg·kg −1 to 246.44 mg·kg −1 . The aqueous solubility of TOL increased in the presence of MTBE, suggesting that the reduction in adsorption capacity for TOL can be attributed to co-solvent effects. Regarding the co-solvent effects of MTBE on reducing the adsorption capacity and enhancing the bioaccessibility of TOL in soils, the combined effects should be considered seriously when assessing the health risks associated with exposure to TOL and MTBE co-contaminated soils. • The impact of TOL and MTBE coexistence on their oral bioaccessibility was evaluated. • MTBE increased the bioaccessibility of TOL in gastrointestinal phases. • The HPCD and DCM/Ace fractions were predominant fraction in gastrointestinal phases. • The co-solvent effects of MTBE reduce the adsorption capacity of TOL in soils. • The coexistence effects should be considered seriously when evaluating health risks.