Benzyl alcohol

Toxicity to microorganisms

Description of key information

 The 24h-EC50 of 390 mg/L for Nitrosomonas from the study by Blum & Speece (1991) is regarded to be the most adequate value to describe the toxicity of benzyl alcohol in the STP.

Key value for chemical safety assessment

EC50 for microorganisms:

390 mg/L

Additional information

Several publications on the toxicity of benzyl alcohol to different micro-organisms such as Escherichia coli (Bringmann & Kühn 1959a), Photobacterium phosphoreum (Ferard et al.1983, Kaiser et al. 1987), Nitrosomonas & aerobic heterogens (Blum & Speece 1991) as well as Pseudomonas putida (Knie et al. 1983, Trenel & Kühn 1982) and two publications on the toxicity to the ciliates Microregma (Bringmann & Kühn 1959b) and Tetrahymena (Schultz et al.1996) are available and indicate low toxicity of benzyl alcohol to micro-organisms. In addition a respiration inhibition test using activated sludge is available (Weytjens 1989).

In accordance with the Endpoint Specific Guidance RIP 3.2 (Chapter R.7B, Section 7.8.17), the results of single species tests with e.g. Vibrio fisheri(formerly known asP. phosphoreum) or E. coli (Bringmann & Kühn 1960) cannot be used for determination of the PNECstp as they use glucose as substrate (nor is E. coli a bacterium that will tend to multiply in an activated sludge environment). Likewise V. fisherirequires a high salinity environment. Therefore, the studies by Bringmann & Kühn (1959a), Ferard et al. (1983) and Kaiser et al. (1987) are not considered as relevant for the environmental risk assessment.

The toxicity tests described in the remaining studies are summarized in the following:

• Knie et al. (1983): The toxicity of benzyl alcohol to bacteria was assessed in a cell multiplication inhibition test according to Bringmann & Kühn (1979). The test duration was 16 -18 hours and Pseudomonas putida was used as test organism. The growth of bacteria was assessed by measuring the degree of opacity before and after the exposure period. The EC10 was determined to be 658 mg/L. The present publication has been assessed in the US EPA Document (1989) and the OECD SIDS Report (2001) and was used as critical study for the derivation of the SIDS endpoint.
• Blum (1991): The toxicity of benzyl alcohol to microorganisms in the sewage treatment plant was assessed in a test for inhibition of oxygen consumption of aerobic heterotrophs and a test for inhibition of ammonium consumption of Nitrosomonas. The test organisms were obtained from the mixed liquor of an activated sludge sewage treatment plant. The IC50 for aerobic heterotrophs and Nitrosomonas were determined to be 2100 mg/L (49h) and 390 mg/L (24h), respectively. The present publication has been assessed in the OECD SIDS Report (2001) and the results were not used for the derivation of the SIDS endpoint.
• Trenel & Kühn (1982): The toxicity of benzyl alcohol was assessed in a cell multiplication inhibition test according to Bringmann & Kühn (1977) using Pseudomonas putida as test organism. The 18h-EC10 was determined to be > 100 mg/L.
• Schultz et al. (1996): The toxicity of benzyl alcohol to the ciliate Tetrahymena pyriformis was assessed in a 2 -day growth inhibition test. The population densities were measured spectrophotometrically. The EC50 (48h) was determined to be 892 mg/L.
• Bringmann & Kühn (1959b): The toxicity of benzyl alcohol to protozoan Microregma heterostoma was assessed on the basis of the inhibition of food intake after 28 hours exposure. The inhibition of food intake was assessed by comparing the cell density of the bacterium Escherichia coli, which serves as food for Microregma, at the beginning of the test with the density of the bacterium at the end of the test and with the untreated control by means of nephelometric measurements. The results showed that the inhibition of food intake of the protozoan species after 28 hours exposure starts at 200 mg/L.
• Weytjens (1989): The inhibition of the respiration rate of activated sludge in the presence of benzyl alcohol was investigated according to the OECD Guideline 209. The concentrations tested were 100, 320, 1000, 3200 and 10,000 mg/L. The respiration rate was measured after a contact time of 30 minutes and 3 hours. The EC50 value after 3 hours exposure was determined to be 1385 mg/L.

Since nitrifying bacteria, such as Nitrosomonas, have a higher sensitivity to toxicants than the other species tested (see Endpoint Specific Guidance, Chapter R7b, Section R.7.8.17), the 24h-EC50 of 390 mg/L for Nitrosomonas from the study by Blum & Speece (1991) is regarded to be the most adequate value to describe the toxicity of benzyl alcohol in the STP.