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Environmental fate & pathways

Hydrolysis

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Description of key information

Half-life of 40.1 days at pH 7 and 25 °C (Kuet, 2002)
Normalised half-life of 113.5 days at 12 °C

Key value for chemical safety assessment

Half-life for hydrolysis:
40.1 d
at the temperature of:
25 °C

Additional information

A number of studies are available concerning the hydrolysis of CGA154281 (benoxacor).

The first study (Warren, 1986) investigated the degradation of benoxacor through hydrolysis. Only minimal hydrolysis was observed at pH 3. The half-lives at pH 7 and pH 11 were estimated to be 46 and 19 days, respectively. This non-guideline study was conducted to GLP.

In the second study (Spare, 1987) benoxacor was found to undergo significant hydrolysis at pH 7.0 and 9.0 with half-lives of 56 and 13 days, respectively. No significant hydrolysis was observed at pH 5. This GLP-compliant study was conducted to US EPA guideline for hydrolysis and is considered to be reliable without restrictions.

The third study (Kuet, 2002) was a GLP-compliant study conducted to OECD111. This study is considered to be reliable without restrictions. Hydrolysis was negligible at 25°C at pH 4.0 and pH 5.0. The reported half-lives for benoxacor at 25°C were 40.1 and 24.2 days at pH 7.0 and pH 9.0, respectively. Hydrolysis was faster at higher temperatures.Only one major degradation product was formed, CGA 201068, which was identified at levels up to 40.6 and 56.4% at pH7 and pH 9, respectively at 25°C.

Based on the above information, it is concluded that benoxacor is hydrolytically stable under acidic conditions at environmentally relevant temperatures, but prone to hydrolysis under neutral or basic conditions.Under neutral conditions the degradation half life is relatively slow (between 46 and 56 days), but increases with increasing pH (pH9 the DT50 is 13 days). The key value selected for the chemical safety assessment is a half life of 40.1 days at pH 7 and 25 °C, taken from the study by Kuet (2002). This study is considered to be the most reliable as it is the most recent and was performed according to the OECD guideline.