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Clarified slurry oil (CSO, CAS #64741–62-4; also termed carbon black oil), a residual product from the fluidized catalytic cracker in petroleum refining, has the potential to be absorbed through the skin. The reproductive toxicity of CSO in male and female rats was evaluated by the topical route of exposure. CSO was administered dermally to male rats at dosages of 0 (vehicle), 0.1, 1, 10, 50, and 250 mg/kg/day for 70 days before a cohabitation period with untreated female rats. CSO was administered also to female rats at the same dosages for 14 days prior to a 7-day cohabitation period and continuing until Day 0 of gestation (day spermatozoa was present in a smear of the vaginal contents or a copulatory plug was observed in situ). The dosage volume in both experiments was 1 ml/kg, adjusted on each day of dosage based on individual body weights recorded immediately before application of CSO. Under the conditions of these experiments, the paternal no-observable-adverse-effect-level (NOAEL) for CSO administered dermally was 1 mg/kg/day. The 10, 50, and 250 mg/kg/day dosages of CSO caused body weight losses and/or decreased body weight gains and reduced feed consumption. The 50- and 250-mg/kg/day dosages also caused adverse clinical effects. No mating, fertility, or testicular end points in male rats were affected by the highest dosages tested; therefore, the reproductive NOAEL for male rats is <250 mg/kg/day. The maternal NOAEL for CSO administered dermally was 10 mg/kg/day. The 50-and 250-mg/kg/day dosages of CSO reduced body weight gains; 250 mg/kg/day also reduced feed consumption. There were no adverse effects on gonadal function, estrous cycles, mating behavior, conception rates, or reproductive organ weights; therefore, the reproductive NOAEL for female rats administered CSO dermally is at least 250 mg/kg/day.

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