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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Testing is waived on the basis that the chemical safety assessment according to Annex I indicates that it is not necessary to conduct the simulation test on ultimate degradation in surface water and the sediment simulation test, or to identify degradation products.

Simulation tests (water and sediments) are not considered necessary because:

  • The risk characterisation ratios (RCRs) for the aquatic and sediment compartments, based on the assumption that the silanol hydrolysis product is not biodegradable, are <1.
  • The substance is used under highly controlled conditions and, therefore, exposure of the aquatic environment, and thus the sediment compartment, is low
  • The silanol hydrolysis product has a low log Kow value and, therefore, exposure of the sediment compartment is expected to be low.

Standard biodegradation testing is not applicable to the inorganic hydrolysis product ammonia.

Ammonia or ammonium ion is rapidly converted to nitrate by nitrification under aerobic conditions in the aquatic environment. Ammonia is part of the nitrogen cycle. As the ammonium salts are inorganic salts, standard biodegradation tests cannot be performed. However,it is known that ammonia (NH3or NH4+) is easily mineralised to nitrite ion (NO2-) by numerous species of bacteria such as Nitrosomonas europea, Nitrosococcus, Nitrosospira. (OECD, 2007).

OECD (2007). SIDS Initial Assessment Report for SIAM 24, Paris, France, 17-20 April 2007, Ammonia Category.