Effects of Octamethylcyclotetrasiloxane (Omcts) on Freshwater and Marine Organisms

Abstract

The toxicity of octamethylcyclotetrailoxane (OMCTS) to representative freshwater and marine fish and invertebrates was investigated. Testing procedures followed Toxic Substance Control Act (TSCA) guidelines with chemical-specific adaptations as presented in the OMCTS Testing Consent Order (Docket OPTS-42071A). The physicochemical properties and behavior of OMCTS (i.e., high volatility, low water solubility) precluded the use of conventional experimental practices and exposure systems. Procedures and systems developed during these investigations provided a mechanism that produced exposure levels equal to the maximum achievable (i.e., "functional") solubility of OMCTS in natural dilution waters. The toxicant delivery systems and exposure chambers were designed to minimize volatilization by elimination of the air/water interface. The flow-through systems maintained consistent exposure concentrations and adhered to U.S. Environmental Protection Agency (EPA) Guideline test performance criteria. The "functional" water solubility of OMCTS in freshwater and seawater ranged from 14 to 30 pg/L and from 6.0 to 9.0 pg/L, respectively. Functional water solubility appeared to vary slightly with test conditions and dilution water characteristics. Continuous exposures of 2 to 93 d were conducted during these investigations with daphnids (Daphnia magna), rainbow trout (Oncorhynchus mykiss), mysids (Mysidopsis bahia), and sheepshead minnow (Cyprinodon variegatus). The rainbow trout was determined to be the most sensitive species to OMCTS (14-d LC50 = 10 pg/L). At levels equal to the functional water solubility, OMCTS was not acutely toxic to D. magna, mysids, or sheepshead minnow. The survival of D. magna was reduced by l6%, relative to the control organisms, after 21-d exposures to 15 pg/L OMCTS; exposure to 7.9 pg/L OMCTS or less had no effect on daphnid survival or reproduction. No toxicity was observed at the highest concentration tested in a 93-d exposure of rainbow trout early life stages. The no-observed-effect concentration for this study was 4.4 pg/L, the same as determined in a 14-d extended acute study.

Fate of Octamethylcyclotetrasiloxane (Omcts) in the Atmosphere and in Sewage Treatment Plants as an Estimation of Aquatic Exposure

“…No acetylene water data have been found in the literature because of its aqueous instability; thus, a dashed line is used for its equilibrium concentration in water. Based on the Los Angeles data, the maximum concentrations of OMCTS expected in waters of the continental U.S. are approximately lop5 pg/L, more than five orders of magnitude lower than the chronic no-observed-effect concentration (NOEC) for trout of 4.4 pg/L [12].…”

“…375 times less than average acetylene atmospheric concentration Table 4 with the expected variability over the continental U.S. The concentrations in water, sediment, and soil are orders of magnitude lower than present-day detection limits of -0.1 pg/L liquid [12] and -0.2 pg/kg sludge [5]. Figure 5 summarizes the fate of acetylene and OMCTS in air, and in water in equilibrium with air.…”

Bioconcentration by fish of a highly volatile silicone compound in a totally enclosed aquatic exposure system

“…*To whom correspondence may be addressed. Presented at the Symposium on Interagency Testing Committee Recommendations Under TSCA Section 4: A Case Study with Octamethylcyclotetrasiloxane (OMCTS), 13th Annual Meeting, Society of Environmental Toxicology and Chemistry, Cincinnati, Ohio, November [8][9][10][11][12]1992.…”

The potential of methylsiloxanes as solvents for synthetic chemistry applications

“…Three of the analysed VMSs (MD 3 M, D 4 and D 5 ) present some health risks of comparable magnitude to some of the traditional organic solvents included in the assessment, although these are less than those of the non-polar solvents for which the VMSs are likely replacements (see below). Whereas MD 3 M and D 5 are irritants, D 4 is believed to impair fertility [35][36][37] and to exhibit estrogenic behaviour in rats and mice (see, for example, ref. 38 and 39).…”