Disposition of Decamethylcyclopentasiloxane in Fischer 344 Rats Following Single or Repeated Inhalation Exposure to ¹⁴C-Decamethylcyclopentasiloxane (¹⁴C-D₅)

Abstract

The disposition of decamethylcyclopentasiloxane (D₅) in male and female Fischer 344 rats following single or repeated inhalation exposures was evaluated. Animals were administered a single 6-h nose-only exposure to 7 or 160 ppm ¹⁴C-D₅ or fourteen 6-h nose-only exposures to unlabeled D₅ followed on day 15 by a 6-h exposure to ¹⁴C-D₅. Subgroups of exposed animals were used to evaluate body burden, distribution, elimination, and deposition on the fur. Retention of radioactivity following single and repeated exposures was relatively low (approximately 1–2% of inhaled D₅). Radioactivity and parent D₅ were widely distributed to tissues of both male and female rats, with the maximum concentration of radioactivity observed in most tissues by 3 h postexposure. Fat was a depot for D₅, with elimination occurring much slower than observed for plasma and other tissues. In all groups, the primary route for elimination of radioactivity was through expired air. Analyses for parent D₅ indicated that essentially all the radioactivity in the expired volatiles was unchanged D₅. Repeated exposure gave rise to higher levels of parent D₅ in the lung and fat of both sexes and in female liver relative to the single exposure. In fat, immediately after sacrifice approximately 50% of the radioactivity was attributed to parent. Five polar metabolites of D₅ were identified in urine, with no parent D₅ detected. Radiochromatograms demonstrated two peaks in feces. One corresponded to the retention time for D₅. The second has been putatively identified as hydroxylated D₅.