Ethanone, 2,2-dichloro-1-(2,3-dihydro-3-methyl-4H-1,4-benzoxazin-4-yl)-

Long-term toxicity to aquatic invertebrates

Description of key information

A study of long-term toxicity of benoxacor to freshwater invertebrates (Daphnia magna) is available. The study was carried out to the ASTM 1980 guideline. The 21-day NOEC for benoxacor was 0.354 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.354 mg/L

Additional information

The key study (Hamaker, 1986) investigated the toxicity of the substance to the waterflea (Daphnia magna). The study followed the ASTM 1980 guideline, which is similar to the OECD 211 guideline, and was GLP compliant. This study is considered to be reliable with restriction (Klimisch 2), as no analysis was performed to confirm initial nominal exposure concentrations or to confirm the stability of the substance under flow-through exposure concentrations. However, due to the flow-through conditions with a flow rate of 5 test chamber replacements/day the opportunity for the chemical to degrade was limited. This seems to be confirmed by analytical information provided in other laboratory aquatic toxicity studies demonstrating that dissipation is not a critical issue. For example, in a prolonged (21 day) toxicity study on rainbow trout under flow-through conditions, Grade (1992) reported that mean measured concentrations did not fall below 78% of nominal rates. Thus, it is considered that dissipation would be relatively minor in the flow-through study presented here. This is also supported by the finding that hydrolysis of the substance is slow (DT50 = 40.1 days) and that the half-life for photodegradation in water of 1 hour is long enough to ensure that the nominal test concentrations obtained by dosing in time intervals of 36 minutes were maintained throughout the duration of the test. Accordingly, it is proposed that the study should be considered to be reliable with restrictions. The key value used in the chemical safety assessment is therefore the NOEC of 0.354 mg benoxacor/L.