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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 n-Butyl acrylate is introduced into biological treatment plants in appropriately low concentrations.
EC0 (3d) > 150 mg/L (domestic activated sludge, BOD Test)
TTC = 3.5 mg/L (Chilomonas paramaecium, cell multiplication inhibition test)

Key value for chemical safety assessment

Additional information

In a microbial inhibition test, 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 (BAMM 1995).

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 butyl acrylate on activated sludge.

This conclusion is supported by data from the structurally-related iso-Butyl acrylate. A respiration inhibition test was performed according to OECD TG 209 and in compliance with GLP using activated sludge from a laboratory wastewater plant treating municipal sewage as inoculum (BASF AG 2001). The EC20 (nominal) after an incubation time of 30 min was determined to be greater than 1000 mg/L.

But the most sensitive microorganism to n-Butyl acrylate was the protozoan Chilomonas paramaecium with a 48-hour Toxicity Threshold of 3.5 mg/L determined in a cell multiplication inhibition test (Bringmann 1980). Although this species does not influence the degradation processes in a wastewater treatment plant itself, it is necessary for a proper function of a WWTP and therefore shall be taken into consideration for the derivation of the PNEC STP (Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.10, ECHA, May 2008).

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