1-isopropyl-2,2-dimethyltrimethylene diisobutyrate

Endpoint summary

Additional information

Acute Toxicity

A number of acute aquatic toxicity studies have been conducted on this substance. Due to the material having a low water solubility, all of the studies were conducted using methods to prevent testing at concentrations above the solubility limit. The material is a difficult substance to study and water solubility values range from 0.9 -13 mg/L. One acute toxicity study was conducted utilizing seven species in the same exposure (1 fish species and 6 invertebrate species). In this study a column elution method was used to provide an exposure solution at the limit of solubility. Measured concentrations were reported as 1.46 mg/L for the 48 hour daphnia endpoint and 1.55 mg/L for the 96 hour endpoints for the other species tested. For all seven species tested there were no adverse effects observed (NOEC at saturation limit). An additional acute study was conducted with bluegill sunfish using a flow-through system. The highest nominal concentration in that study (5.0 mg/L) was established at what was determined to be the solubility limit. No adverse effects were observed at the highest concentration (6.0 mg/L mean measured) of that study (NOEC at saturation limit). An algal study was conducted with a range of nominal concentrations, some of which exceeded the water solubility limit. In this study the 72 hour EC50 for growth rate was greater than the highest concentration tested (nominal 30 mg/L, geometric mean measured 7.49 mg/L). Based upon a weight of evidence approach, all of the results from acute toxicity tests tend to demonstrate that acute toxicity is not demonstrated at the limit of water solubility.

Chronic Toxicity

In addition to the OECD 201 algal inhibition study, a 21 day daphnia study utilizing a flow-through system and equivalent to a OECD 211 study was performed. In the daphnia study the highest test concentration was established at 2.0 mg/L (nominal) which was believed to be the limit of solubility. Results from that study indicated that the 21 -day EC50 for immobilation was greater than the highest concentration tested (2.0 mg/L nominal, 1.3 mg/L mean measured). However, the endpoint of reproduction was more sensitive resulting in a statistically significant effect at the highest test concentration (LOEC of 1.3 mg/L mean measured, 2.0 mg/L nominal) and a NOEC of 0.7 mg/L mean measured (1.0 mg/L nominal). In the algal study it was recognized that absorption to the test vessels as well as the algal cells themselves would cause an apparent loss of the test material during analytical verifications. In an attempt to counteract these anticipated losses, the test vessels were pre-conditioned with the test substance as well as introducing the substance at nominal concentrations high enough to achieve mean measured concentrations up to the water solubility of the substance. Many of the test concentrations were dosed at levels above the solubility of the test substance. Despite the measure to counteract losses, the losses ranged from 75.7% to 93.4%. The results of the test indicated that the EC50 for growth rate was greater than the highest test concentration (30 mg/L nominal, 7.49 mg/L mean measured). The study reported a NOEC of 2.25 mg/L mean measured (13.3 mg/L nominal). However, the statistical analyses of the NOEC was reported as being a T-test as opposed to the method requirements which would utilize an ANOVA followed by the appropriate multiple comparison test. Re-analyses of the data according to the method requirements resulted in a NOEC of 3.56 mg/L mean measured (20 mg/L nominal).In addition, the two highest mean measured concentrations, 7.49 and 3.56 mg/L, exhibited only 14.9% and 5% inhibition respectively. The OECD 201 guideline indicates that there is a recommendation of abandoning the concept of NOEC and replacing it with a regression based point estimate EC value. The appropriate EC value has not been established for the algal study but a range of 10 to 20% appears to be appropriate. In this study the highest concentration (30 mg/L nominal, 7.49 mg/L mean measured) resulted in ~14.9% inhibition of growth rate which approximates an EC15.With the water solubility of this substance being in the range of 0.9 - 13 mg/L, it is difficult to definitively determine if chronic toxicity is demonstrated at the solubility limit. The results of the algal study NOEC for growth rate at a mean measured concentration of 3.56 mg/L, which was derived from a nominal concentration (20 mg/L) that was greater than the water solubility limit, suggest that chronic toxicity is not demonstrated for algae at the limit of water solubility. In the daphnia study the most sensitive endpoint of reproduction provided a LOEC of 1.3 mg/L mean measured (2.0 mg/L nominal) and a NOEC of 0.7 mg/L mean measured (1.0 mg/L nominal). Because NOEC and LOEC values can only correspond to defined exposure concentrations, it is possible that the true NOEC could be at another concentration between the LOEC and NOEC which would be at or near the water solubility of this substance. Therefore, it can be concluded that chronic toxicity to daphnia may occur at or near the water solubility of the test substance.