Pulmonary Bioavailability and Fine Particle Enrichment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Respirable Soil Particles

The pulmonary bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) and the enrichment of polychlorinated dioxins (PCDDs)and furans (PCDFs) in fine particles were evaluated to assessthe implications that these factors have on risk and exposureassessments. Respirable subfractions of PCDD-contaminated soilfrom a former 2,4,5-trichlorophenoxyacetic acid manufacturingsite were isolated by chemical dispersion and gravity sedimentation.Analysis of the subfractions revealed that there was a size-dependentenrichment of PCDDs and PCDFs, with smaller particles more highlycontaminated. TCDD was enriched up to 33-fold as compared tounfractionated soil. Soil and laboratory-recontaminated galliumoxide, which served as the positive control, were administeredby intratracheal instillation to female Sprague-Dawley rats.Animals were terminated up to 28 days following treatment andpulmonary bioavailability of TCDD was assessed by hepatic enzymeinduction and TCDD concentration. Enzyme induction was dependenton the duration of exposure with up to 56 and 918% increasesin cytochrome P450 and aryl hydrocarbon hydroxylase (AHH) activity,respectively, following exposure to PCDD-contaminated soil.There was no significant difference in AHH induction betweenanimals which received contaminated soil and those treated withthe positive control. Hepatic concentration of TCDD in soil-exposedrats was 115, 101, and 179% of positive controls at 1, 7, and28 days post-treatment, suggesting that the soil or co-contaminantsinfluenced retention of TCDD in the liver. These data indicatethat the relative pulmonary bioavailability of TCDD on respirablesoil particles is 100% as compared to laboratory-recontaminatedgallium oxide and that PCDDs and PCDFs are highly enriched onrespirable particles. Utilization of these results will reducethe uncertainty and improve the accuracy of envi ronmental riskassessments of PCDDs and PCDFs.