2-methylpentane-2,4-diol

Toxicity to microorganisms

Description of key information

In a non-guideline study conducted prior to ecotoxicity GLP requirements, hexylene glycol was found to have an ECo (equivalent to a NOEC) of 200 mg/L in Pseudomonas aeruginosa, indicating low toxicity.  This is consistent with it being readily biodegradable and non-toxic in tests of biodegradation in water.  Supporting data from a poorly documented luminescence study in Photobacterium phosphoreum indicate a 5-minute EC50 of 3070 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

200 mg/L

Additional information

The toxicity of hexylene glycol Pseudomonas aeruginosa (ATCC 15442) was assessed in a published non-guideline study that predates GLP requirements for ecotoxicity studies (Daugherty, 1980). This study used a static freshwater system. Cell culture was maintained on nutrient agar slants and examined for purity periodically. The inoculum was prepared by growing the microorganisms on nutrient agar plates for 24 hours then transferring the cells to a Kolle flask of nutrient agar and incubating for 6 hours. The cells were washed from the medium and then centrifuged and washed 3 times at 6000 rpm for 15 minutes and resuspended in a basal salts medium. The cells were left at a final resuspension volume of 16 cm³ basal salts medium and counted by pour-plate colony counts to determine the number of bacteria/cm³. The resuspension was held at room temperature for 24 hours before inoculation to reduce endogenous growth. At time 0, the cells were washed once, centrifuged at 6000 rpm, and resuspended. The suspension was diluted so that it contained approximately 50-500 microorganisms/cm³, based on the colony count. One cm³ of this diluted inoculum was then delivered aseptically into a 250 cm³ flask containing 100 cm³ sterile basal salts medium (pH 7.0-7.3) and the desired concentrations (v/v) of the test substance (ranging from 0.05 to greater than 3000 ppm, based on graphical data presented in the publication). Flasks were agitated in a shaking incubator at 25ºC and the bacterial growth was measured by pour-plate colony counts at 3, 7, and 10 days. Each experiment was performed in duplicate and reproduced at least twice. Growth noted in the control flasks (containing basal salts medium only) was subtracted from the final data. No positive control was tested. Pseudomonas aeruginosa grew on the test substance in concentrations up to about 2000 ppm. The optimum concentration for growth was 200 ppm and the test substance appeared to be inhibitory for growth at concentrations greater than 1000 ppm (Daugherty, 1980). The results indicate that the no-observed-effect-concentration (NOEC) was 200 ppm (approximately 200 mg/L).

Supporting data are derived from another static freshwater study that also was not conducted according to OECD guidelines and that predates GLP requirements for ecotoxicity studies (Curtis et al., 1982). This study examined the effect of a 5-minute incubation with hexylene glycol on luminescence in Photobacterium phosphoreum. The 5-minute EC₅₀value was determined to be 3070 mg/L. Documentation was insufficient to fully assess this study (Curtis et al., 1982).