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Toxicity to aquatic algae and cyanobacteria

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Description of key information

72h EC50 >87.3 mg/l, 72h NOEC 69.9 mg/l for Pseudokirchnerella subcapitata

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
69.9 mg/L

Additional information

Two studies are summarised on the algal toxicity of the test material.

1. A study was carried out with Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum) according to OECD, EEC and ISO test guidelines and under GLP (Geurts and Van Wijk 2001, Rel. 1, Key study). The guidelines were slightly modified to ensure good growth and pH control of the cultures.

The test was carried out on equimolar amounts of NaHEDTA.2H20 and FeCl3.6H20 and at nominal concentrations of 60, 80 and 100 mg/l (concentrations represented as H4.EDTA).

Due to photodegradation, the test substance concentration declines during the test. The chemical analyses carried out showed that the concentration at the end of the test had decreased to about half of the concentration at the beginning of the test. The mean concentrations during the 72 hours of testing for the nominal concentrations of 60, 80 and 100 mg/l as measured by chemical analyses were 38.1, 48.4 and 60.6 mg/l, respectively.

The test was conducted in a mineral salt medium in a climatized illuminated orbital incubator. The maximum variation in pH in the test media was 1.4 pH unit. The definitive test is valid as shown by the increase of the extinction of the control over 72 h by a factor of 489.

The EbC50and ErC50 are both higher than 100 mg/l based on nominal concentrations and higher than 60 mg/l based on the mean measured concentrations of H4.EDTA. Recalculated to the test substance the 72h-EC50s are above 87.3 mg/l.

The NOEC and LOEC based on nominal concentrations are 79.4 mg/l and 99.9 mg/l (H4-EDTA). Based on the mean measured concentrations the NOEC and LOEC are 48.4 and 60.6 mg/l (H4-EDTA). Recalculated to the test substance, the 72h-NOEC = 69.9 mg/l.


2. The European Union Risk Assessment Report Edetic Acid (EDTA) of 2004 reviews a study on the acute toxicity of equimolar amounts of Na4 -EDTA and Fe(III) towards Scenedesmus subspicatus. No inhibition was found up to a nominal concentration of 100 mg Na4EDTA. This implies that the NOEC expressed as the test substance is > 110.7 mg/l.