Determination of the dietary biomagnification of octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane with the rainbow trout (Oncorhynchus mykiss)

Abstract

Separate 77-d fish feeding studies were conducted on the cyclic volatile methylsiloxane (cVMS) chemicals octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane with the rainbow trout, Oncorhynchus mykiss, with the determination of biomagnification factor (BMF) and lipid-adjusted BMF (BMF(L)) values as the final experimental metrics. The studies used fish food concentrations of ∼500μgg−1 for exposure periods of 35d, followed by a depuration period of 42d with clean food. The fish tissue concentrations of D4 and D5 achieved empirical steady-state by day 21 in each study. By day 7 of exposure, total 14C activity of both compounds had moved from the fish gastrointestinal (GI) tract into surrounding tissue. An absence of significant fish growth during the initial depuration phase allowed for measurement of empirical depuration rate constants (k2) independent of growth dilution for D4 and D5 of 0.035 and 0.040d−1, respectively, corresponding to elimination half-lives of approximately 20d. These rate constants indicated that ∼70–75% of steady-state was achieved during exposure in both studies, resulting in empirical steady-state BMF and BMF(L) values of 0.28 and 0.66 for D4, respectively, and 0.32 and 0.85 for D5, respectively. Kinetic modeling using simple first-order uptake and depuration dynamics produced good agreement with experimental data, with D4 and D5 assimilation efficiencies of 40% and 44%, respectively. Growth-corrected depuration rate constants modeled over the entire study data set indicated slower elimination kinetics for D4 (k2 of 0.007d−1 or half-life of 100d) compared to D5 (k2 of 0.010d−1 or elimination half-life of 69d). Kinetic BMFk values (i.e., k1/k2) for D4 and D5 were 1.7 and 1.3, respectively, with lipid-adjusted BMFk(L) values of 4.0 and 3.4, respectively.