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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Toxicity to aquatic algae: ECr50 (72h) = 2.9 mg/L ; NOEC (72h) = 0.92 mg/L (OECD TG 201)

Key value for chemical safety assessment

EC50 for freshwater algae:
2.9 mg/L
EC10 or NOEC for freshwater algae:
0.92 mg/L

Additional information

A key study (GANCET C. 2003) is available for this endpoint. A second reliable study (WARD T.J., WYSKIEL D.C. and BOERI R.L. 2003) is available but has not been selected as key study because the EC50 and NOEC values were determined on the initial measured concentrations although the final measured concentrations were < 1 to 68% of nominal concentrations. In this case, the geometric mean concentration should have been used as the basis for assessing effects (in accordance with OECD series on testing and assessment No. 23: Guidance document on aquatic toxicity testing of difficult substances and mixtures) leading to a 72h EC50 between 0.46 and 1.2 mg/L. In order to clarify these conclusions, the study selected as key study has been performed and is describedbelow. A third study (STEPHENSON R.R., 1982), not considered reliable because of its significant methodological deficiencies (96h acute toxicity test with 48h measurement episode, no raw data to check the validity criteria, no analytical monitoring performed,...) is not developed in this endpoint summary.


The key study was conducted in accordance with the OECD guideline 201 and in compliance with OECD (1997) Good Laboratory Practice standards. OECD validity criteria were fulfilled.

The determination of the growth inhibition was performed on the freshwater algae Pseudokirchneriella subcapitata with an exposure to the test item n-HEPTANAL for a duration of 72 hours.

The test was performed under static conditions in sealed containers in which there was no headspace. Nominal concentrations of heptanal were 0 mg/L (control with and without algae), 5, 7.9, 12.6, 20, 31.5 and 100 mg/L. Initial measured concentrations of heptanal were: <QL ( below the limit of quantification; control), 4.36, 5.49, 12.6, 19.1, 25, and 87.8 mg/L. Final measured concentrations were below the limit of quantification or below the limit of detection, except for the two highest tested concentrations (i.e. 31.5 and 100 mg/L) were 6.31 and 86.9 mg/L were found respectively, corresponding to 25.23 and 101.99% of the initial measured concentrations respectively. Knowing the potential of oxidation of heptanal into heptanoic acid, the concentrations of heptanoic acid (CAS RN 111-14-8) have also been measured in the non inoculated flask. These measurements showed that heptanoic acid is present at t0 in the 3 highest test concentrations solutions and at t72h in the 4 highest test concentrations solutions. However, considering that heptanoic acid is less toxic than heptanal, and since the final measured concentrations in non-inoculated flasks were found to be lower than 80 % of the initial concentration, estimation of effective concentration (EC50) was based on geometric average value of initial and final concentrations of heptanal.


The results obtained were as follows:

72h-ErC50 = 2.9 mg/L (growth rate)

72h-EbC50 = 0.42 mg/L (biomass)

72h-NOErC = 0.92 mg/L (growth rate)

72h-NOEbC = not determined


Based on these results,Heptanal should be classified as toxic to the aquatic organisms tested in accordance with the Directive 67/548/EC.

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