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Ecotoxicological information

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An acute fish toxicity study according to OECD TG 203 was conducted with read across material MPAAU (Pupp 2012). The active substance caused no mortality to Fathead minnow (Pimephales promelas) after 96-hours exposure at the nominal concentration of 583 mg/L in a static test, and a nominal 96h-LC50 of 934.1 mg/L could be determined. Resulting from an acute Daphnia toxicity study (Kamp 1995) with read across substance MPAAU according to OECD-Test Guideline 202, the EC50 value was calculated as being 350 mg/L for the active substance. An algal growth inhibition study (Kley 2012) with read across substance MPAAU revealed following results for growth rate: 72h-EC50 = 43.1 mg/L, 72h-EC10 = 13.5 mg/L, 72h-NOEC value = 3.2 mg/L. Therefore, the algae should be considered as the most sensitive of the tested freshwater organisms. Information on long-term toxicity for fish and daphnids is currently not available.

The L(E)C50 values are based on studies on MPAAU and so the actual concentration of MPA needs to be determined. MPAAU is a composed of 1 part MPA and 1 part AU. Using the molecular weight of each substance the nominal concentration of MPA in the study can be determined and the endpoint for MPA determined accordingly. Converting a weight/weight concentration of MPAAU into a weight/weight concentration of MPA the molecular weight of MPA has to be divided by the molecular weight of MPAAU. The molecular weight of MPA is 96. The molecular weight of MPA is 198. 96/198 = 0.48. Therefore the relevant endpoint value for a study on MPAAU can be multiplied by a factor of 0.48 to determine to endpoint value for MPA.

The EC50 for algal growth inhibition 43.1 mg/L is for MPAAU and therefore the EC50 for MPA can reduced to 21.6 mg/L (EC10 = 6.75 mg/L, NOEC = 1.6 mg/L). In the same way the LC50 for fish can be calculated to 467 mg/L, and for Daphnia 175 mg/L.

In a valid, reliable and conclusive study according to OECD TG 209 (2010), the effect of the test item Methyl phosphonic acid 70 % on the respiration of activated sewage sludge micro-organisms gave a 3-Hour EC50 value of greater than 1000 mg ai/L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 100 mg ai/L.