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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

A study was not carried out on the chemical NaDMH, three studies were however carried out on the analogue chemical DMH and are to be considered for the purposes of read-across.
The studies provided show that DMH was steadily degraded at 20 °C in the absence of light giving whole system and aqueous phase DT50 values of 13 to 24 days and DT90 values of 42 to 79 days. After 17 weeks, 65% of initial radioactivity was mineralised to CO2.

Key value for chemical safety assessment

Half-life in freshwater:
12.7 d
at the temperature of:
293 K

Additional information

The key study has been performed to an appropriate guideline under GLP in an artificial water/sediment system and a natural system for a period of 120 days. DMH is a polar molecule and was expected to be retained mainly in the surface water phase and be exposed to predominently aerobic conditions. The fastest degradation rates were observed in the water rather than the whole system. 90 % degradation of DMH was observed after 42 to 79 days in the two water/sediment systems with more rapid degradation in the natural system . 50 % degradation of DMH was observed after 13 to 24 days for both systems. The most environmentally relevant half life in water was 12.7 days in the natural water.

There are two supporting studies for aerobic and anaerobic degradation performed to old EPA guidelines which have been superseded by OECD 308. Both studies were performed on a single sediment type and the study methods have clearly defined limitations. The Schmidt & Stansbrey study indicated the formation of at least two unidentified degradation products under anaerobic conditions after one year. In the aerobic study (Schmidt,1993) only a small amount of DMH mineralisation to CO2 (<6% of initial measured dose) after one year under aerobic conditions.

As previously stated these studies have been performed on DMH (Dimethyl Hydantoin) and have been used for read-across purposes. A summary of data for read-across of NaDMH with DMH is given in Section 13.