Sodium [N-[2-[bis(carboxymethyl)amino]ethyl]-N-(2-hydroxyethyl)glycinato(4-)]ferrate(1-)

Toxicity to aquatic algae and cyanobacteria

Description of key information

72h EC50 >72.5 mg/l, 72h NOEC 58.5 mg/l for P. subcapitata as HEDTA-FeNa.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

58.5 mg/L

Additional information

The following studies are avialable on the algal toxicity of test materials.

1. A study was carried out with Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum) (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 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 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 HEDTA-FeNa the 72h-EC50s are above 72.5 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 HEDTA-FeNa, the 72h-NOEC = 58.5 mg/l.

 

2. A guideline study with DTPA-FeNaH (Kean, 2013) with P. subcapitata and including attempts to address for the chelating properties as well as colour of the test solution. This substance caused coloration of the test solutions and proved photolabile. A significant decline of most of the test concentrations was evident, but observed unexpected results wrt measured concentrations were not explained. A NOEC > 1 mg/L was confirmed by measured and nominal concentrations indicating little concern for the aquatic environment, however as there is some unclarity wrt geometric mean measured concentrations, these results were not considered key.

3. Additional confirmation of the toxicity of chelants, associoated with the scavenging of essential micronutrients was provided in the two additional studies. First, the illustration by Dufkova (1984) that no negative influence to algae growth was observed when the concentration of nutrients in solution was increased, corresponding to the increased EDTA concentration. In addition, 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.

 

The most relevant and concrete data wrt toxicity to algae is considered the first study by Geurts & van Wijk and these endpoints are considered to be relevant for HEDTA-FeNa, based on the read-across justification as provided in section 13.

The chelation of essential nutrients is not considered a relevant environmental hazard, due to the abundance of these nutrients in the aquatic environment.