BIOCONCENTRATION BY FISH OF A HIGHLY VOLATILE SILICONE COMPOUND IN A TOTALLY ENCLOSED AQUATIC EXPOSURE SYSTEM

Two aqueous exposures of fathead minnows (Pimephales promelas) were co nducted to determine the bioconcentration factor (BCF) for [C-14]octam ethylcyclotetrasiloxane (OMCTS). The high volatility, high sorptive ca pacity, and low water solubility of OMCTS required that the testing be conducted in a novel, totally enclosed, flow-through exposure system that prevented the volatilization of the test substance. In a prelimin ary study, fish were continuously exposed to OMCTS at a concentration of approximately 0.5 mu g/L for 6 d. In the definitive study, fish wer e exposed for 28 d at approximately 0.3 mu g/L. In each case, OMCTS ex posures were followed by a 14-d depuration period. Water concentration s and fish residues were measured periodically in both studies. Data f rom the 6-d study resulted in a maximum measured BCF of 7,000. Model c alculations based on data from the 6-d exposure phase predicted a stea dy-state BCF of 10,000 after 19 d of exposure. The definitive study re sulted in a steady-state measured BCF of 12,400 after 28 d of exposure . Model calculations based on the measured data from the 28-d exposure phase provided an estimated BCF of 13,400. The OMCTS bioconcentration factors could be accurately estimated from the data produced during a 6-d continuous exposure. The use of innovative test systems was key t o the development of useful bioconcentration data.