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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Tert-butyl acrylate is acutely toxic to freshwater algae.

ErC50 (72 h, growth rate) = 14.6 mg/L (measured) (Desmodesmus subspicatus, OECD TG 201)

Key value for chemical safety assessment

Additional information

An acute toxicity study was conducted with Desmodesmus subspicatus (BASFSE, 2002) according to OECD Guideline 201 using a static design and closed test vessels. Nominal exposure concentrations were 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50, 100 mg/L. The analytical recovery rate was in all analysed test solutions below 80 %. Thus, the effective concentrations were based on the median analytical recovery rate of 30.8 % (all measurements between 0 and 72 h). 72-hour EC50 values for growth rate and biomass were 14.6 and 4.34 mg/L (measured), respectively. The No Observed Effect Concentration was determined to be 3.85 mg/L.

In addition, there is an older study with Scenedesmus subspicatus conducted according to the national German standard DIN 38412, part 9 using Tween 80 as solubilizer (BASF AG, 1989). The 72 hours EC50 was determined to be 280 mg/L (biomass) based on nominal test concentrations. This study does not take the possible decrease in test concentration by volatilisation of the substance into consideration and therefore is not suitable for the assessment (no analytical monitoring, open test vessels).

Since tert-butyl acrylate is of considerable volatility and moderately biodegradable, only test results from the study with analytical monitoring and in closed system were used for the hazard assessment for freshwater algae.

Supporting data from other acrylates

In addition, a robust data set of acute studies is available from the other members of the acrylic ester category (n-butyl, ethyl, 2-ethylhexyl, isobutyl and methyl acrylate).

Several (individual) studies were performed to determine the toxicity of various acrylates (n-butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, isobutyl acrylate and methyl acrylate) towards freshwater algae. In these studies, all performed according OECD201 and in compliance with GLP criteria, algae (either Pseudokirchneriella subcapitata or Desmodesmus subspicatus) were exposed up to concentrations of 38 mg/L (methyl acrylate), 60 mg/L (n-buyl acrylate), and 100 mg/L (ethyl acrylate, 2-ethylhexyl acrylate and isobutyl acrylate). Cells were counted every 24 hours to determine cell concentrations. Test concentrations were analytically verified, but did not remain within 80 - 120% of the nominal concentrations. Therefore, the effect concentrations are based on the arithmetic means of the measured concentrations. The 72-h ErC50 values for 2-ethylhexyl acrylate, isobutyl acrylate and methyl acrylate were determined to be 1.71, 5.28 and 3.55 mg/L respectively. The 72-h EbC50 values for n-butyl acrylate and ethyl acrylate were determined to be 2.65 and 4.5 mg/L. ErC10 values were calculated to be 0.8 and 2.09 mg/L for 2-ethylhexyl acrylate and isobutyl acrylate, respectively.

Overall, the data of other acrylates supports the finding of the acute toxicity test with tert-butyl acrylate (BASFSE, 2002). Members of the acrylic ester category show comparable toxicity values towards freshwater algae.