Phenanthrene release from natural organic matter surrogates under simulated human gastrointestinal conditions.

The aliphatic region of natural organic matter (NOM) can retain polycyclic aromatic hydrocarbons (PAH) due to the presence of non-polar binding sites. Thus NOM may act as a vehicle for entry of PAH into the gastrointestinal system in man and animals. In this study, the release of phenanthrene from the aliphatic NOM surrogates cutin and cutan was measured under simulated human gastrointestinal formulations using three treatments designed to simulate the biological and chemical conditions of the gastrointestinal environment. The three experimental treatments were composed of fecal microorganisms, chyme, and chyme+fecal microorganisms. Water was used as a control treatment. Phenanthrene laden biopolymer and a C18 membrane were immersed in each treatment. Phenanthrene was extracted from each membrane and measured with HPLC. Membrane-associated phenanthrene was taken to represent the fraction that had desorbed from the biopolymer. Cutin was found to yield an average phenanthrene release 55% higher than cutan (94% vs. 39%). A significant decrease (p<0.05) in phenanthrene release was observed in both the chyme and chyme+fecal microorganism treatments as compared to the water treatment (control). The presence of enteric microorganisms did not significantly influence phenanthrene release and did not reduce phenanthrene bioaccessibility in gastrointestinal chyme. Over 80% of the phenanthrene in cutin was recovered in the C18 matrix and its relative amount was uninfluenced by the treatments. For cutan, only 25-50% of the phenanthrene was recovered, suggesting that cutin-associated phenanthrene was more loosely bound. These data demonstrate that the fractions of NOM retained phenanthrene to a varying extent and thus the predictions of phenanthrene bioavailability should also be assessed on the basis of the constituents of the NOM matrix.