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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Environmental fate screening (river-die-away-test) of IPPD for biological and chemical transformations was carried out in Mississippi River water (active and sterile) and purified water at an initial concentration of 1000 µg/L. Half-lives for IPPD ranged from 2.5 to 11 hours (Monsanto, 1981) These results only reflect the primary degradation of the substance.

Key value for chemical safety assessment

Half-life in freshwater:
2.5 h

Additional information

The result from the natural Mississippi water was taken as key value.

The distribution modelling shows that the substance is to a high degree transported to the aqueous environment (about 88%) The biodegradability in water is limited but abiotic degradation by hydrolysis is the main degradation pathway which occurs rapidly within 3.9 hours at relevant environmental conditions.

Aquatic biodegradation data showed 18.9 % biodegradation. Therefore IPPD is not ready biodegradable and it is concluded that biodegradation in the sediment compartment will not occur to a relevant extent. Furthermore, the distribution modelling shows that the substance is to a high degree transported to the aqueous environment (about 88%) whereas only about 4% are expected in sediment. The biodegradability in water is limited but abiotic degradation by hydrolysis is the main degradation pathway. Thus, as sediment also consists of a water phase, hydrolysis is also expected in that compartment. Adsorption to soil particles might also play a role. However, the Koc of 246.8 indicates only a moderate potential for adsorption. For this reason hydrolysis is considered as the main relevant degradation pathway of the substance in sediment.

A MacKay level III fugacity model (presented in the SIDS report, 2000) yielded a more detailed description of the substance in the sediment compartment: The results show that IPPD released via the water phase leads to negligible exposure of the sediment (0.1%). Released directly to soil will not result in any significant percentages in sediment. It should be mentioned here that direct release to water and soil are the main routes for environmental exposure, concerning manufacture and DU uses as well as the release from tyres.