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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

EC50 (72h): >=100 mg/L; NOEC (72h): 100 mg/L for EDTA-Na4, corresponding to 72.6 mg/L for HEDTA-H3.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
72.6 mg/L

Additional information

In accordance with ECHA guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance, the EC50 endpoint based on growth rate is used in PNEC derivation. This is because use of values based on biomass cannot be applied to an analysis of results from a system in exponential growth without logarithmic transformation.

One study of low reliability is available regarding an assessment of toxicity to freshwater algae and aquatic plants. Results indicate an EC50 of 26 mg/L. The EC50 (72h) of HEDTA to Skeletonema costatum in marine water was estimated as 4.9 mg/L based on growth rate.

The marked inhibitory effect of the structurally similar substance, Na4-EDTA, on the cell multiplication of Scenedesmus subspicatus was shown to be caused by the complexing essential ferrous ions in the assay. This secondary effect was demonstrated using a modified test system without iron limitation when it was shown that the simultaneous application of equimolar concentrations of FeCl3*6H20 and EDTA up to 263.04 umol/L (100 mg/L Na4-EDTA) produced no inhibition of algal growth. The same is expected to occur with HEDTA. It is generally accepted that studies in which secondary effects have demonstrably affected outcome should not be used in the derivation of PNECs.