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Ecotoxicological information

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MCA is a weak acid (pKa = 2.86) under environmental conditions MCA will occur in anionic or salt form e.g. sodium monochloroacetic acid (SMCA). Therefore ecotoxicological data from both MCA and SMCA can be used for hazard and risk assessment.

Algae are the most sensitive species to MCA. This is not surprising, because MCA is a known herbicide. The lowest long-term result is the NOEC of 5.8 μg/L for Scenedesmus subspicatus (NOACK 1992). This test results is used for PNEC-derivation in the EU-RAR.

It should however be noted that in the REACH guidance’s it has been identified that NOEC and LOEC values should be used with caution as they are influenced by the dosing regime and the statistical power of the test and that an EC10 for a long-term test which is obtained using an appropriate statistical method (usually regression analysis) should be used preferentially. OECD recommended even in 1996 to phase out the use of the NOEC, in particular as it can correspond to large and potentially biologically important magnitudes of effect.

In the same algae study with Scenedesmus subspicatus also an EC10 of 7 µg/L for growth was derived. It is suggested to use this value in stead of the 5.8 µg/L for the PNEC derivation.