Age effect on perfluorooctanoate (PFOA) plasma concentration in post-weaning rats following oral gavage with ammonium perfluorooctanoate (APFO)

The relationship between age and plasma concentration of perfluorooctanoate (PFOA) in young rats was investigated. The study was conducted in two phases in which male and female rats between 3 and 8 weeks of age were administered the ammonium salt of PFOA (APFO) by single oral gavage at either 10 or 30 mg/kg. In Phase I, APFO was administered at a dose of 10 mg/kg body weight to 27-, 34-, 38-, 48-, and 55-day-old male and female rats. Plasma was collected 24 h after the dose. In Phase II, APFO doses of either 10 or 30 mg/kg body weight were given to groups of 23-, 30-, and 32-day-old male and female rats, and plasma was collected at 2 and 24 h after the dose (separate groups), and urine was collected for 24 h. PFOA concentrations were measured by LC/MS/MS. In Phase I, plasma concentrations of PFOA were not dependent on age for rats 5 weeks of age and older; however, in 4-week-old rats, male plasma PFOA concentrations were 5–6 times lower than during weeks 5–8, and female plasma PFOA concentrations were 2.5–4 times higher than subsequent weeks. In Phase II, plasma samples collected 2 h post-dosing indicated no significant difference in the PFOA uptake by age in females; although, in males, plasma PFOA concentrations were significantly less in 32-day-old rats, approximating one-half of the values observed at 23 and 30 days of age. Plasma samples collected 24 h after dosing from 3- to 5-week-old rats indicated a slightly but significantly higher male plasma concentration at 30 and 32 days of age as compared to 23 days of age for the 30 mg/kg dose group only. Significantly lower (approximately 10-fold) plasma PFOA concentrations occurred in 32-day-old females as compared with 23- and 30-day-old females at both 2 and 24 h after the dose. Although statistically significant changes in urine PFOA concentrations did not occur between age and dose groups within sex, urine PFOA concentrations generally supported plasma elimination. At 23 days of age, the ratio of male to female plasma PFOA concentrations was approximately 2–3:1 compared to approximately 30:1 at 32 days of age. An unexplainable inconsistency in PFOA plasma concentrations for both sexes was noted when comparing Phase I values for 27-day-old rats to Phase II values for 23- and 30-day-old rats. The Phase I values for the 27-day-old rats of both sexes were five to six times lower than Phase II values for the 23- and 30-day-old rats. However, Phase I values for 34-day-old rats were comparable to Phase II values for 32-day-old rats. Despite this anomaly between the 23-, 27-, and 30-day-old rat values, there is strong evidence that age-dependent changes in the elimination of PFOA develop in female rats between 3 and 5 weeks of age, with a consistent marked difference occurring after 30 days of age.