Disodium [N,N-bis[2-[bis(carboxymethyl)amino]ethyl]glycinato(5-)]ferrate(2-)

Toxicity to aquatic algae and cyanobacteria

Description of key information

A well performed study with DTPA-FeHNa is available. However, due to the photo-instability of the compound and coloration of test solutions, actual measured concentrations showed unexpected results, making it difficult to conclude based on these geometric mean measured values. Still, based on actual and nominal concentrations the chronic ErC10 value was confirmed > 1 mg/L, indicating low hazard to the environment.

Key value for chemical safety assessment

EC50 for freshwater algae:

9.8 mg/L

EC10 or NOEC for freshwater algae:

1.83 mg/L

Additional information

A well performed study with DTPA-FeHNa is available, trying to mitigate chelating and coloration effects in the test design. However, due to the photo-instability of the compound and coloration of test solutions, actual measured concentrations showed unexpected results, making it difficult to conclude based on these geometric mean measured values. Still, based on actual and nominal concentrations the chronic ErC10 value was confirmed > 1 mg/L (1.75 and 6.6 mg/L respectively for DTPAFeHNa). ErC50 values were 9.4 and 70.2 mg/L respectively for DTPAFeNaH. For DTPAFeNa2 this would give actual EC10 and EC50 values of 1.83 and 9.8 mg/L respectively.

The other algal study available for DTPA was deemed not reliable (Klimisch = 3) mainly due to the fact that the observed effects were due to nutrient limitation and not inherent toxicity of the test substance.  This is supported by the following studies with EDTA, which can be used for read across, as justified in section 13 of IUCLID.

- Compensatory adjustment of the algal media was performed in an algal test with EDTA-Na2H2. 2H₂O (Dufkova, 1984). Dufková (1984) demonstrated withScenedesmus quadricaudathat it was not the absolute EDTA concentration, but rather the ratio of the EDTA to the bivalent cations that is crucial to algae growth. Higher concentrations (400 mg/L EDTA-Na2H2. 2H₂O), when in surplus over trace elements in the nutrient solution, inhibited cell division, chlorophyll synthesis and the production of algal biomass, especially in the earlier phase of algae growth. No negative influence was observed when the concentration of trace elements in the nutrient solution was increased corresponding to the increased EDTA concentration. Thus, the NOEC and EC50 values based on growth inhibition of Scenedesmus quadricaudawere greater than 400 mg/L EDTA-Na2H2. 2H₂O. 

- Additionally, a study is available withPseudokirchneriella subcapitata(formerly known asSelenastrum capricornutum) according to OECD, EEC and ISO test guidelines and under GLP (Geurts and Van Wijk, 2001. The guidelines were slightly modified to ensure good growth and pH control of the cultures. The test was carried out on equimolar amounts of EDTA-Na2H2.2H20 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 declined 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 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 EDTA-H4. Recalculated to the substance EDTA-FeNa.3H2O 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 (EDTA-H4). Based on the mean measured concentrations the NOEC and LOEC are 48.4 and 60.6 mg/l (EDTA-H4). Recalculated to the substance EDTA-FeNa.3H2O, the 72h-NOEC = 69.9 mg/l.

- The European Union Risk Assessment Report Edetic Acid (EDTA) of 2004 reviews a study on the acute toxicity of equimolar amounts of EDTA-Na4 and Fe(III) towards Scenedesmus subspicatus. No inhibition was found up to a nominal concentration of 100 mg EDTA-Na4. This implies that the NOEC expressed as the substance EDTA-FeNa.3H2O is > 110.7 mg/L.