Soil adsorption alters kinetics and bioavailability of trichloroethylene in orally exposed female rats

Bioavailability of 2,3′,4,4′,5-pentachlorobiphenyl (PCB118) and 2,2′,5,5′-tetrachlorobiphenyl (PCB52) from soils using a rat model and a physiologically based extraction test

The bioavailability of coplanar 2,3',4,4',5-pentachlorobiphenyl (PCB118) and nonplanar 2,2',5,5'-tetrachlorobiphenyl (PCB52) from soils representing a range in organic carbon (OC), clay content and pH were investigated using an in vivo rat model and an in vitro physiologically based extraction test (PBET) to assess the role of soil and chemical properties on bioavailabilty. Affinity to soil and persistence of PCBs have been shown to increase with increasing soil organic carbon (OC) content, PCB chlorination, and PCB coplanarity. In the in vivo tests for both PCB118 and PCB52, the AUCs following iv injection were significantly higher than the AUCs for all soil groups, indicating that the soil matrix can reduce the absolute bioavailability of PCB118 and PCB52. However, no significant differences were detected between soils of different properties. In the in vitro PBET, significant differences in the mobilization of PCB118 and PCB52 were observed among soils, and PCBs had the least mobilization from the soil with the highest OC content consistent with hydrophobic partitioning theory. Also, significantly less PCB118 was mobilized relative to PCB52 in the PBET assay, showing the potential impact of spatial orientation and chlorine content on bioavailability. No correlation between the in vitro PBET and the in vivo rat model was observed for the PCBs. Although the in vitro PBET and related assays may serve as an indicator of bioavailability, it is likely to underestimate what can be released from a soil in an in vivo assay.

Oral bioavailability of pentachlorophenol from soils of varying characteristics using a rat model

Evidence accumulated during the last two decades suggests that only a fraction of any chemical in soil is available to organisms, and soil-related effects on bioavailability should be considered in optimizing soil remediation cleanup levels. In the current study, the absolute and relative bioavailabilities of pentachlorophenol (PCP) from freshly spiked and environmentally aged soils varying in organic carbon content, clay content, and pH were examined using a rat model. PCP is a broad-spectrum biocide widely used as a wood preservative, and thus is ubiquitous in the environment. Soils and corn oil containing equivalent levels of PCP were administered to male Sprague-Dawley rats by gavage at 2 dose levels: 100 and 200 microg/kg body weight. Equivalent doses were also given intravenously. The areas under the plasma concentration of PCP versus time curves were calculated, and absolute and relative bioavailabilities of PCP from each soil were determined. At a dose of 100 microg/kg body weight, the absolute bioavailabilities of PCP across soils ranged from 36% to 65%, and the relative bioavailabilities ranged from 48% to 82%. At the higher dose level (200 microg/kg body weight), absolute and relative bioavailability ranges were somewhat higher at 46% to 77% and 52% to 87%, respectively. All soils decreased absolute PCP bioavailability significantly at both dose levels and relative bioavailability at the lower PCP dose level. At the higher dose level, only one of the two field-contaminated soils decreased the relative PCP bioavailability. The data indicate that PCP-soil interactions do significantly decrease the oral bioavailability of PCP from soil, but no obvious correlation was observed between soil properties and bioavailabilities.

Trichloroethylene metabolism in vitro: an EPR/SPIN trapping study

Trichloroethylene (TCE) was hypothesized to produce free radicals which could be detected using electron paramagnetic resonance spectroscopy with the spin trap, PBN (alpha-phenyl tert-butyl nitrone). The free radicals detected following incubation of precision cut liver slices in media containing 10 mM PBN had hyperfine coupling constants aN = 1.61 mT and aH = 0.325 mT. There was a linear increase in free radicals detected in the bathing media when the headspace TCE concentration was increased from 2500-10000 p.p.m. The levels of conjugated dienes measured in the slices incubated in PBN supplemented media were less than slices exposed to TCE in incubation media without PBN. The PBN trap may act as a scavenger preventing the propagation of free radicals and inhibiting lipid peroxidation. The experiments suggest that free radical formation by TCE leads to a concomitant increase in conjugated dienes in liver slices which may contribute to the pathological changes which occur in liver following TCE exposure.