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

Short-term toxicity to fish

Description of key information

Eight reliable short-term toxicity studies to fish have been carried out for benoxacor. The lowest reliable endpoint value for freshwater fish (Ictalurus punctatus) is 1.4 mg/L.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

1.4 mg/L

Additional information

Studies on the toxicity of benoxacor to four different types of fish have been conducted by Rufli (1989, a, b, c and d). These studies were GLP compliant, used semi-static systems and were conducted to OECD 203 guideline.

The study investigating toxicity to rainbow trout (Oncorhynchus mykiss) provided a LC50 of 6.6 mg/L and a NOEC of 1.11 mg/L (Rufli, 1989c) and is considered to be reliable with restriction (Klimisch 2). Loss of equilibrium was observed among surviving fish exposed to a treatment level of 10 mg/L, erratic swimming behaviour at 3.2 mg/Land change in pigmentation was observed in the 5.8 mg/L treatment level.

The study conducted on channel catfish (Ictalurus punctatus) provided the lowest value for this endpoint (Rufli, 1989a). This study was considered to be reliable without restriction (Klimisch 1). The 96h LC50 was calculated to be 1.4 mg/L based on mean measured concentrations. NOEC was not determined for this test. Loss of equilibrium was observed among surviving fish exposed to a treatment level of 0.77 mg/L, erratic swimming behaviour and change in pigmentation was observed in the 0.44 mg/L treatment level. 

The toxicity test carried out on common carp (Cyprinus carpio) resulted in a LC50 of 10 mg/L and a NOEC of 7.1 mg/L (Rufli, 1989d). Sublethal effects observed were loss of equilibrium (18 mg/L) and erratic swimming behaviour (18 mg/L). This study is considered to be reliable with restrictions (Klimisch 2).

The test investigating short-term toxicity effects of benoxacor to bluegill (Lepomis macrochirus) provides LC50 and NOEC values of 6.5 mg/L and 2.9 mg/L, respectively (Rufli, 1989b). Sublethal effects (loss of equilibrium, erratic swimming behaviour and change in pigmentation) were observed among surviving fish exposed to a treatment level of 10 mg/L. This study is considered to be reliable with restrictions (Klimisch 2).

In addition, the prolonged short-term toxicity of benoxacor to rainbow trout (Oncorhynchus mykiss) was investigated (Grade, 1992) according to OECD guideline 204. The study was GLP compliant and is considered to be reliable without restriction (Klimisch 1). The overall 21-day NOEC of benoxacor to juvenile Oncorhynchus mykiss under flow-through conditions was 0.004 mg/L (nominal), based on change in a calculated condition index. The overall 21-day LOEC and LC50 endpoints were 0.016 and 0.51 mg benoxacor/L (nominal), respectively.

Hamaker (1986a) investigated the toxicity of benoxacor to rainbow trout (Oncorhynchus mykiss) using a static system, according to ASTM 1980 guideline. The study provided values for LC50 and NOEC of 3.5 and 1.25 mg/L, respectively, was GLP compliant and is considered to be unreliable (Klimisch 3).

Toxicity to rainbow trout (Oncorhynchus mykiss) was investigated by Drottar (1987a) according to EPA OPP 72-1 in a GLP compliant study considered to be reliable with restrictions (Klimisch 2). The study reported LC50 and NOEC values of 2.4 and 1.16 mg/L, respectively.

A toxicity study by LeLievre (1991a) provided a LC50 of 2.9 mg/L and a NOEC of 1.2 mg/L. Five different test concentrations were used in this test. 100% mortality was observed among fish exposed to the two highest concentrations (10 and 5.8 mg/L). Surviving fish at both the 2.9 and 1.8 mg/L test concentrations exhibited adverse sublethal effects (e. g. darkened pigmentation). This GLP compliant study was conducted to OECD 203 guideline and is considered to be reliable without restrictions (Klimisch 1).

The results of the acute toxicity testing on fish are summarised below:

Species	length (mm) / weight (g)	LC50 [mg ai/L]	NOEC [mg ai/L]	Reference
Rainbow trout (Oncorhynchus mykiss)	25 / 1.08	3.5	1.25	Hamaker 1986a
Rainbow trout (Oncorhynchus mykiss)	46 / 1.4	2.4	1.16	Drottar 1987a
Rainbow trout (Oncorhynchus mykiss)	39/0.58	2.9	1.2	LeLievre 1991a
Rainbow trout (Oncorhynchus mykiss)	47 / 1.15	6.6	1.11	Rufli 1989c
Catfish (Ictalurus punctatus)	66 / 2.35	1.4	0.77[1]	Rufli 1989a
Bluegill sunfish (Lepomis macrochirus)	42 / 0.91	6.5	2.9	Rufli 1989b
Common carp(Cyprinus carpio)	51/ 1.83	10	7.1	Rufli 1989d
Rainbow trout (Oncorhynchus mykiss)	69 / 3.32	0.51[2]	0.004	Grade, 1992

[1] LC0 -Sub-lethal effects were seen in all of the test treatments in the Rufli (1989a) study

[2] prolonged short-term toxicity: 21-day LC50 and NOEC

 

From the results presented above, it can be seen that the most sensitive fish species tested to short-term toxicity was the channel catfish (Ictalurus punctatus) with an LC50 of 1.4 mg/L (Rufli, 1989a). Additionally, a prolonged short-term study has provided a value of 0.51 mg/L for the 21-day LC50 of benoxacor to rainbow trout (Grade, 1992).