Propan-2-ol

Toxicity to microorganisms

Description of key information

The 16 hour Toxicity Threshold concentration of 1050 mg/L for Pseudomonas putida (Bringmann & Kühn, 1980) is selected as the value to use for PNECstp calculations.
Toxicity Threshold = 1050 mg/L; 16 hours, Pseudomonas putida (Bringmann & Kühn, 1980)
Toxicity Threshold = 1050 mg/L; 16 hours, Pseudomonas putida (Bringmann & Kühn, 1977)
Toxicity Threshold = 4930 mg/L; 72 hours, Entosiphon sulcatum (Bringmann, 1978)
Toxicity Threshold = 3425 mg/L; 20 hours Uronema parduzci (Bringmann, 1980)
Toxicity Threshold = 104 mg/L; 48 hours Chilomonas paramaecium (Bringmann et. al., 1980)

Additional information

The toxicity of 2-propanol to Pseudomonas putida was assessed in a published non-guideline study that predates GLP requirements for excotoxicity studies (Bringmann & Kühn 1980). The 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 microorganism on nutrient agar plates for 24 hours. The cells were washed off from the medium and resuspended in a nutrient medium. By determining the extinction of the monochromatic radiation at 436 nm for a 10 mm layer of the bacterial suspension, the final turbidity value of the bacterial suspension was adjusted, by means of sterile saline, such that it corresponded to the extinction value of a Formazin standard suspension TE/F/436 nm = 10.

 

Four parallel dilution series in 300 mL Erlenmeyer flasks were prepared of test solution. Each dilution contains 1 part v/v of test solution in 2⁰ to 2¹⁴parts v/v mixture. The first flask in the series contained 160 mL of test solution at the start. Starting from this flask, the subsequent dilution steps were prepared at a constant dilution ratio by consistently mixing 80 mL of preliminary test dilution and 80 mL double distilled water. Consequently, each flask contained 80 mL of culture liquid at the start. Each flask of the three dilution series were inoculated to 100 mL by adding 5 mL each of stock solution I, 5 mL of stock solution II and 10 mL each of the prepared bacterial suspension from the preliminary culture. Both inoculated and non-inoculated flasks were incubated at 25ºC for 16 hours. After 16 hours, the extinction of the monochromatic radiation at 436 nm for a 10 mm layer of the bacterial suspension was determined.

 

The results were analyzed on a semi-logarithmic chart according to the following scheme. The calculated values (A), (A-3%), and (B) were located on the Y-axis (linear): the average (A) of all the absorbance of the non-inhibited and non-stimulated cultures (as long as those values were below a standard deviation of less than 3 %); and the average (B) of all the absorbance of the cultures showing the lowest toxic effect. The highest non-toxic concentration (a) and the lowest toxic concentration (b) were located on the X-axis.

 

The placing of (A-3 %) on the line between the coordinates (a, A) and (b, B) allowed the value (C) to be determined on the abscissa of the initial concentration at which growth inhibition was determined or Toxicity Threshold. The Bringmann & Kühn (1980) results indicate that Pseudomonas putida had a 16 hour Toxicity Threshold concentration of 1050 mg/L.

 

None of the five published studies presented documenting the toxicity of 2-propanol to microorganisms were conducted with a mixed inoculum that would asses the functioning of the entire microbial community in a sewage treatment plant, rather the tests were based on single species systems. According to the ECHA Guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance section R.7.8.17.1 Laboratory data on toxicity on sewage treatment plant microorganisms, results of the cell multiplication inhibition test with P. putida (Bringmann and Kühn 1980) can be used for calculation of the PNECstp.

 

The supporting data report higher Toxicity Thresholds for Entosiphon sulcatum (flagellated protozoa) (Bringmann, 1978) and Uronema parduzci (ciliated protozoa) (Bringmann, 1980) and a lower Toxicity Threshold for Chilomonas paramaecium (flagellated protozoa) (Bringmann et. al., 1980). According to the ECHA Guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance section R.7.8.16.1 Laboratory data on toxicity to STP microorganisms and its sources, no correlation exists between activated sludge and ciliated protozoa test results. The lower Toxicity Threshold is for flagellated protozoa and a contact time of 48 hours.  In general in accordance with the hydraulic retention time in a sewage treatment plant, short-term toxicity measurements in the order of hours are preferred. As these three protozoan results are equal to or greater than 20 hours contact time, these results should not be used to determine the PNECstp.