Metabolism of 14 C-octamethylcyclotetrasiloxane ([ 14 C]D 4 ) or 14 C-decamethylcyclopentasiloxane ([ 14 C]D 5 ) orally gavaged in rainbow trout (Oncorhynchus mykiss).

•Metabolism of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) occurs in rainbow trout orally (relevant route for hydrophobic chemicals) gavaged with these materials in a corn oil vehicle.•Blood elimination half-lives are 39 and 70h for D4 and D5, respectively.•D4 and D5 are metabolized in rainbow trout with similar estimated biotransformation half-lives (t1/2) of less than 7 days.•Clearance may occur via enterohepatic circulation of metabolic products in bile with excretion via the digestive tract and urinary clearance of metabolites.