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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 72 hour ErC50 value for EDDHMA-Fe with Selenastrum capricornutum was 71 mg/L and the ErC10 was 2.8 mg/L based on nominal concentrations and growth rate. Conclusions related to effects on algae should be used with care.

Key value for chemical safety assessment

EC50 for freshwater algae:
71 mg/L
EC10 or NOEC for freshwater algae:
2.8 mg/L

Additional information

One study with EDDHMA-Fe is available to study potential effects to algae and one study with the structurally related EDDHA-FeNa. Both substances cause a strong coloration of test solutions, limiting exposure to light, introducing difficulties in interpreting the results in a reliable manner. Also, the chelating properties could cause disturbances when micronutrients are deprived. In both studies no attempt was made to optimise micronutrient supply to exclude nutrient deprivation. The Bogers study concludes however on the minor effect of coloration, but whether the substance will interact with algae by contact can not be concluded (fish show coloration of fins when exposed). Both substances are expected to be readily photodegraded in lower concentrations, however only the Basf study indicates the decline of concentrations during the study. On the other hand, both studies conclude chronic toxicity end-points in the same order of magnitude and > 1 mg/L indicating they should not be considered hazardous to the aquatic environment.

- Key study with Selenastrum capricornutum (Bogers, 1996)

The study procedures described in this report were based on the EEC Directive 92/69, Publication No. L383 Part C-3 adopted December, 1992; OECD guideline No. 201, Adopted June 7, 1984; and IS0 Standard 8692, First edition, 15 November 1989.

The results showed that no inhibition of cell growth occurred when algal suspensions were exposed to light filtered through colored solutions up to 100 mg/L. A final EC50 -test was performed exposing exponentially growing algal cultures to EDDHMA- FeNa concentrations ranging from 1.0 to 100 mg/L. Cell densities were based on microscopical counting. At the start of the test, the actual test concentrations were in agreement with nominal (96 -101%). At the end of the 72 -hour period the measured concentration had not decreased by more than 20% in any of the samples analysed.

The color of the test solutions did not significantly contribute to the effect on algal growth. The EC50 for growth rate reduction (ErC50: 0 -72h) was a factor of 5 higher than the EbC50 :0 -72h, i.e. 71 mg/L (95% confidence limits: 54 and 93 mg/L), whereas the ErC10:0 -72h was only a factor of 2 higher (2.8 mg/L). The EC50 for inhibition of total cell growth (EbC50: 0 -72h) was 14 mg/L with a 95% confidence interval ranging from 10 to 22 mg/L. The EC10 for cell growth (EbC10: 0 -72h) was 1.4 mg/L.

- In a supporting study the the toxic effects of EDDHA-FeNa (Basf, 2010) on the growth of single-cell green algae as representatives of primary producers in freshwater plankton over a 72 hour static exposure period were determined according to the principles of OECD-Guideline 201 and EU method C.3.

Mean measured concentrations were considered to be an accurate representation of exposure levels throughout the exposure period. The 72 hour EC50 value for FeEDDHA with the Desmodesmus subspicatus CHODAT (SAG 86.81) was greater than 294 mg/L and the NOEC was 8.2 mg/L based on mean measured concentrations and growth rate. The 72 hour EC50 based on yield and mean measured concnetrations was 27.3 mg/L and the NOEC was 2.4 mg/L.

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