No abstract

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.

In a previous study, it was demonstrated that mobilization of organochlorine pesticides would be underestimated by an in vitro gastrointestinal model if the sorption of the mobilized pollutants on the digestive residue was not taken into consideration. A multiple fluid/solid ratio procedure was developed to characterize the sorption. In this study, the sorption hypothesis was further tested for polycyclic aromatic hydrocarbons (PAHs), and the sorption of the mobilized PAHs on digestive residue was directly characterized by spiking the gastrointestinal digest with several deuterated PAHs. It was demonstrated that 10-41% of the spiked deuterated PAHs were sorbed on the assimilated residue, which would remain in the solid phase after separation. It appears that the mobility of PAHs would be underestimated if only those dissolved in the fluid is measured. The total mobilized fraction of a PAH compound was defined as a sum of that dissolved in the fluid and that sorbed on the residue. The average mobilized PAH fractions in the studied soils was 70 +/- 24% which was significantly higher than 47 +/- 19% in the fluid. It was also found that the sorption of the mobilized PAHs on the digestive residue was positively correlated with both soil organic carbon (SOC) and molecular weight (MW(t)) of PAHs, and a regression model was developed so that the sorption of different PAHs on soils with different SOCs could be estimated.

This paper focuses on how the electron temperature and other plasma properties affect optical emission and CO2 conversion in a CO2 plasma. Such plasma-mediated reactions can enable efficient CO2 reuse. We study CO2 and CO plasmas generated by inductively-coupled radiofrequency power (30-300 W) at low pressures (6-400 Pa). By varying the argon admixture, we can study the effect of the electron temperature, Te, on the conversion and emission properties using optical emission spectroscopy, mass spectrometry and electrical probe measurements. Importantly, we can observe several parameters simultaneously: Te, CO2 conversion, chemiluminescence from CO2 and dissociation products and optical emission from several atomic and CO transitions and from the C2 Swan system. Based on these results, we establish a correlation between Te, the CO2 conversion and the optical emission spectra. A low Te enhances CO2 conversion and Swan band emission. In contrast with published studies, our results show that the CO2 and C2 vibrations are not in local equilibrium. This means that the vibrational temperatures of CO2 and C2 should differ.