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Toxicity to aquatic algae and cyanobacteria

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Toxicity to aquatic algae and cyanobacteria: Weight of evidence: Experimental results obtained with the substance sodium trichloroacetate in a non standardized test with several species and read-across from results obtained with the substance monochloroacetic acid in two independent studies according to OECD guideline 201 and DIN 38412, Part 9. 

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Toxicity to aquatic algae and cyanobacteria: Weight of evidence: Experimental results obtained with the substance sodium trichloroacetate in a non standardized test with several species and read-across from results obtained with the substance monochloroacetic acid in two independent studies according to OECD guideline 201 and DIN 38412, Part 9.

Sodium trichloroacetate:

Free trichloroacetic acid is a strong organic acid, which forms water-soluble salts with bases. In any medium at or near neutral pH the predominant form present is the trichloroacetate anion. The salts are therefore expected to be toxicologically equivalet to the free acid, except for the acute corrosive properties, which are at least partly determined by the very low pH of strong solutions of the acid.The strongest effects were recorded in a 14-day test with the species Chlorella pyrenoidosa and Chlorella mucosa with EC50 values of 0.3 and 0.46 mg/l, respectively.

Although these results are based on biomass after the exponential growth phase, an analysis of the growth curves reported in the publication shows that the effect concentrations derived from biomass during the exponential growth phase are of the same order as those reported after 14 days. From these results it is concluded that algae is very sensitive to sodium trichloroacetate.

Monochloroacetic acid:

Two studies with Scenedesmus subspicatus were independently performed at two different laboratories. The obtained results for biomass and growth were within the same range, i.e. 25-28 μg/l for biomass and 30-70 μg/l for growth (48-72 hour EC50-values). In the 72 -hour study, the NOEC is 0.0058 mg/l and in the 48 -hour study, the NOEC is 0.007 mg/l (based on biomass) and 0.014 mg/l (based on growth rate).

Based on these results and the molecular weights, the read-across approach is applied and the EC50 (based on growth rate) for sodium trichloroacetate is calculated to be between 0.065 and 0.14 mg/l.

These results, which are below 1 mg/l, support the classification of the substance sodium trichloroacetate as Hazardous for the Aquatic Environment, Acute Category 1.

The substance is already classified in the harmonised list of classification and labelling (CLP Regulation) as Hazardous for the Aquatic Environment, Acute Category 1.

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