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Toxicity to microorganisms

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Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when tert-butyl acrylate is introduced into biological treatment plants in appropriately low concentrations.

EC20 = ca. 950 mg/L (domestic activated sludge, OECD TG 209)

Key value for chemical safety assessment

Additional information

In a test with domestic activated sludge the inhibition of oxygen consumption was examined according to OECD guideline 209 (BASFSE, 1993). After 30 minutes no inhibition of the oxygen uptake was observed at 500 mg/L. The 30-min EC20 was determined to be approx. 950 mg/L. As this test was performed in an open test system without analytical monitoring, the test is valid with restrictions. The considerable volatility of tert-butyl acrylate was not taken into consideration. Also, a Pseudomonas respiration inhibition test was performed according to DIN 38412-27 (BASFSE, 1990). In this study, tert-butyl acrylate was dissolved in Tween 80 and incubated with Pseudomonas putida for 30 minutes with nominal test concentrations of 0 (control), 2500, 5000 and 10000 mg/L. As this test was performed in an open test system without analytical monitoring, the test is valid with restrictions. The EC10 was determined to be 8800 mg/L (nominal).

In accordance with the Guidance on information requirements and chemical safety assessment, Chapter R.10 (ECHA, May 2008), the tested concentration at which toxicity to the microbial inoculum can be ruled out (inhibition control in standardised biodegradation test) can be considered as a NOEC for the toxicity to microorganisms in sewage treatment plants (STP). Therefore, the inhibition control in the CO2-Headspace Test conducted according to ISO 14593 (BASFSE, 2008) can be used as a NOEC value. The test was performed in closed vessels due to significant volatility of test substance. In this study, no toxicity to the microbial inoculum was observed at a concentration of 30.5 mg/L. Therefore, the NOEC value for toxicity to microorganisms is determined to be 30.5 mg/L.

Weight of evidence data from other acrylates

In addition, there are valid experimental data from the other members of the acrylate category, e.g. the structurally related n-butyl acrylate (BAMM, 1995). In a microbial inhibition test according to ASTM STP 528 and in compliance with GLP-criteria, a series of test chambers containing a readily degradable primary substrate (d-glucose), dilution water, and inoculum was dosed with increasing amounts of the test substance. The dissolved oxygen (DO) concentration within each chamber was measured before and after an incubation period of 3 days. Dilution water and primary substrate controls were included and used to check the acceptability of the dilution water and inoculum. Test substance concentrations that inhibited the oxidation of the primary substrate would exhibit an oxygen uptake rate less than that of the primary substrate controls. As inoculum industrial activated sludge was used. Inhibition of oxidation of the primary substrate was not observed over the range of concentrations tested (i.e., 1.0 - 150 mg/L) since the line representing the average DO of the test chambers did not cross above the line representing the average residual primary substrate control DO. Thus, the EC0 (3d) was greater than 150 mg/L indicating no inhibitory effect of n-butyl acrylate on activated sludge.

Taking all these test results into consideration, inhibition of the degradation activity of activated sludge in a WWTP is not anticipated when tert-butyl acrylate is introduced in appropriately low concentrations in WWTPs.