An 18-day Aquatic Toxicity Test of Octamethylcyclotetrasiloxane in Rainbow Trout of Different Size under Flow-through Saturated Conditions (final Report) W-attach & Letter 042392.

摘要

This study evaluated the difference in the toxicity of dimethyl cyclosiloxane fluid in different size trout, and the body burden of dimethyl cyclosiloxane fluid at lethality or test termination. The test material was greater than 99.9% pure. The fish were exposed to dechlorinated municipal water saturated with the test substance for 18 days. Approximately 15 ml of the test substance was poured on the top of the water and then gently stirred with a magnetic stirrer. The fish were exposed to treated and control water in 1.7 liter glass columns that were partially submersed in the water bath. The first exposure occurred when the trout weighed about one gram. The second exposure took place when the trout were approximately 5 grams. All the fish were analyzed by solvent extraction and gas chromatography analysis at the end of the experiment. The fish were weighed and homogenized in distilled water. One or 2 ml of n-pentane containing dodecamethylpentasiloxane was added to the homogenized samples. The n-pentane was extracted and analyzed for the test substance using gas chromatography/mass spectroscopy. Water from the exposure chambers was analyzed for the test substance in the same way as the homogenized fish. The amount of material present was quantified by comparing the total area counts of the unknown versus known standards relative to that of the internal standard. Dissolved oxygen levels and pH were determined 3 times per week. Mortality, narcosis, and any other signs of toxicity were checked daily. The mean concentration of dimethyl cyclosiloxane fluid in the fish during the first exposure was 23.2 ppb, and during the second exposure of the larger fish it was 31.2 ppb. At the end of the experiment with the smaller fish there was 80 % mortality in the exposed group. However, the larger trout exhibited few signs of toxicity and all of the trout survived until the end of the experiment. All fish had substantial amounts of the test substance present following exposure to the test substance. The two small fish that survived were found to have body burdens of dimethyl cyclosiloxane fluid that were 2 to 3 times greater than those that died during the experiment. The bioconcentration factor of dimethyl cyclosiloxane fluid varied between 5000 and 15,000. Dissolved oxygen, temperature, and pH of the exposure and control vessels were within acceptable limits. Dimethyl cyclosiloxane fluid at concentrations of approximately 23 ppb caused a significant number of deaths in the one gram exposed group of trout during 18 days of exposure. The larger trout exhibited no statistically significant alterations in the endpoints observed.