Metabolism of polychlorinated dibenzofurans (PCDFs) in rats

Metabolism of polychlorinated dibenzofurans (PCDFs) was investigated in rats using a mixture of PCDF congeners, including 1,2,7,8-tetra-, 2,3,7,8-tetra- and 1,2,3,7,8-penta-CDFs as major components. The feces of rat dosed with PCDFs were examined for unchanged PCDFs, hydroxylated and sulfur-containing metabolites by gas chromatography (GC) and GC-mass spectrometry. Twelve phenolic PCDFs and four sulfur-containing PCDFs were identified as the metabolites. A dihydroxy-tetrachlorobiphenyl, which has both hydroxy groups at the ortho-position, was also observed. The fecal excretion of unchanged PCDFs and phenolic metabolites were 7 and 32 % of the dose during five days, respectively, while the amount of methylthio-tetra-CDF was 0.01-0.1 % of the dose. It is concluded that hydroxylation is a major metabolic reaction in the metabolism of 1,2,7,8-tetra-, 2,3,7,8-tetra- and 1,2,3,7,8-penta-CDFs, compared to sulfur-containing derivation.