| 2-biphenylol (2BP), 3-biphenylol (3BP), 2,2'-biphenyldiol (2,2'BP), 3,3'-biphenyldiol (3,3'BP), 3-chloro-2-biphenylol (3C2BP), and 4,4'-dichloro-3-biphenylol (4,4'DC3BP), considered to be representative of potential byproducts of Fenton's remediation of polychlorinated biphenyls (PCBs), were studied for the correlation between their chemical/structural properties and observed epigenetic toxicity and cytotoxicity. The scrape-loading/dye transfer (SL/DT) technique was performed to determine the in vitro modulation of gap junctional intercellular communication (GJIC) in a normal rat liver epithelial cell line as a measure of the epigenetic toxicity. Cytotoxicity was determined using the neutral red uptake assay. Only 3,3'BP and 4,4'DC3BP induced cytotoxicity within a dose range of 0 to 300 muM. 4,4'DC3BP was most inhibitory to GJIC at the lowest dose. 3C2BP was least inhibitory to GJIC. Although cells were capable of complete recovery of GJIC after removal of each of the chemicals, only with 2,2'BP and 4,4'DC3BP did the cells demonstrate partial recovery without removal of the chemical. In view of the cytotoxicity and GJIC inhibitory effects observed for 4,4'DC3BP, the PCB congener 4,4'-dichlorobiphenyl (4,4'DCBP) was selected for Fenton's reagent remediation studies. For toxicology studies performed for 4,4'DCBP, over a dose range of 0 to 260.87 muM, very slight to no inhibition of GJIC was observed for incubation times of 30 minutes, 2 hours, 6 hours, and 24 hours.; The methylene blue (MB) dye test was developed to qualitatively indicate the presence of hydroxyl radicals through an immediate, distinct bleaching of the MB dye on a paper test strip. When applied to Fenton's remediation, MB dye tests were capable of indicating the formation of hydroxyl radicals during the Fenton's reaction and indicating the completion of quenching. The presence of hydroxyl radicals was verified by benzoic acid chemical probe hydroxyl radical detection methods using thin layer chromatography (TLC) and spectrophotometric wavelength scans.; Fenton's remediation of 4,4'DCBP in 50/50 Milli-Q water/acetonitrile was performed, followed by an examination of the toxicity of the final Fenton's remediation solution and disappearance of 4,4'DCBP as a result of Fenton's remediation. The Fenton's reaction conditions were pH 3.0, temperature 23.0 °C, Fe2+:H2O2 molar ratio 1:20, initial Fe2+ concentration 0.15 mM, and initial H2O 2 concentration 3 mM. Partial inhibition of GJIC occurred for test volumes greater than 40 muL (30 minute incubation), and a maximum level of inhibition was attained at 60 muL (FOC = 0.75 +/- 0.03). For the time-response GJIC bioassay (60 muL test volume), a maximum level of inhibition was attained at 30 minutes (FOC = 0.78 +/- 0.02), followed by complete recovery of GJIC without removal of the chemical by 240 minutes. Although the final Fenton's remediation solution was determined to be more toxic than the parent PCB, and the inhibitory effects were similar to those observed for 4,4'DC3BP, the byproducts responsible for the toxicity observed could not be ascertained by the detection methods employed. Only 27.22 +/- 1.32% of the 4,4'DCBP remained by 15 minutes of remediation and no further decrease occurred through 60 minutes. |
