Metabolism and disposition of [C]-methylcyclosiloxanes in rats.

Octamethylcyclotetrasiloxane (D) and decamethylcyclopentasiloxane (D) are low molecular weight cyclic volatile methyl siloxanes (cVMSs) primarily used as intermediates or monomers in the production of high molecular weight silicone polymers. The use of D as a direct ingredient in personal care products has declined significantly over the past 20 years, although it may be present as a residual impurity in a variety of consumer products. D is still used as an intentional ingredient in cosmetics, consumer products and in dry cleaning.

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

Critical factors (uptake, distribution, metabolism and elimination) for understanding the bioaccumulation/biomagnification potential of Octamethylcyclotetrasiloxane (D) and Decamethylcyclopentasiloxane (D) siloxanes in fish were investigated to address whether these chemicals meet the "B" criteria of the Persistent, Bioaccumulative, and Toxic (PBT) classification. A metabolism study was conducted in rainbow trout whereby a 15mg [C]D/kg bw or [C]D/kg bw as a single bolus oral dose was administered via gavage. Of the administered dose, 79% (D) and 78% (D) was recovered by the end of the study (96-h).

Strategies to assess systemic exposure of chemicals in subchronic/chronic diet and drinking water studies.

Strategies were developed for the estimation of systemically available daily doses of chemicals, diurnal variations in blood levels, and rough elimination rates in subchronic feeding/drinking water studies, utilizing a minimal number of blood samples. Systemic bioavailability of chemicals was determined by calculating area under the plasma concentration curve over 24 h (AUC-24 h) using complete sets of data (> or =5 data points) and also three, two, and one selected time points. The best predictions of AUC-24 h were made when three time points were used, corresponding to Cmax, a mid-morning sample, and C(min).