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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Isobutyl acrylate is acutely toxic to freshwater algae.
EC50 (72 h, growth rate) = 5.28 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 (BASF AG 2002) according to OECD Guideline 201 using a static design. 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 52.8 % (all measurements between 0 and 72 h). 72-hour EC50 values for growth rate and biomass were 5.28 and 3.18 mg/L (measured), respectively. The No Observed Effect Concentration was determined to be 1.65 mg/L.

These results are supported by data from the structural analogue n-butyl acrylate.

An acute toxicity study was conducted with nBA in Selenastrum capricornutum (BAMM, 1990) according to OECD Guideline 201 using a static design. Based on the arithmetic means for the exposure concentrations (1.8, 3.15, 7.55, 16.5, 34 mg/L) a 96-hour EC50 value of 2.65 mg/L.

In addition, there is an older study with Scenedesmus subspicatus conducted according to the national German standard DIN38412, part 9 without analytical monitoring (BASF AG, 1989). EC50 values after 72 hrs exposure were calculated to be 23.8 mg/L (biomass) and 24.7 mg/L (growth rate), respectively. 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.

Since iBA is readily biodegradable and moderately volatile, only test results from studies with analytical monitoring were used for the hazard assessment for freshwater algae.

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