Pharmacokinetics of fluazifop-butyl in human volunteers. II: Dermal dosing.

1. The absorption of the herbicide fluazifop-butyl (f-b), has been determined from plasma and urine measurements in groups of six male volunteers following dermal administration of 2.5, 25 and 250 micrograms cm-2 from standardized formulations containing 0.05, 0.5 and 5.0% (w/v) fluazifop-butyl to a skin area of 800 cm2. 2. Urinary excretion rate of the principal metabolite fluazifop, following dosing with the 5% formulation, was described by a two-compartment pharmacokinetic model; the average elimination half-lives of initial and terminal phases were 18 h and approximately 70 h, respectively. For the other dose levels the elimination half-life was estimated to be 17 h; urine concentrations at later time points were too low to characterize a second compartment. 3. The estimated total fluazifop-butyl absorbed was 8.0, 3.4 and 1.6% of the applied dose for the 0.05, 0.5 and 5.0% formulations, respectively. 4. Up to 50% of the applied fluazifop-butyl was readily removed by skin washing and the majority of the remainder was transferred to clothing during the 24 h following application. 5. When six volunteers were given a daily dermal dose of the 0.5% formulation for five consecutive days, the plasma and urinary excretion kinetics of fluazifop could be accurately predicted by simple mathematical extrapolation of the kinetic data from the single exposure study at the equivalent daily dose. 6. It is concluded that fluazifop-butyl is only slowly and poorly absorbed through human skin and has a low potential to accumulate in man.