Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-, 1-methylhexyl ester

Short-term toxicity to fish

Description of key information

In order to evaluate the effect of cloquintocet-mexyl to fish, five toxicity tests with four freshwater species were conducted to the OECD guideline 203 for cloquintocet-mexyl. The 96h LC50 of channel catfish to cloquintocet-mexyl is 14 mg/L. 
In the case of the metabolite CGA153433, the lowest reported 96h LC50 is 82.6 mg/L (mean measured) for Bluegill sunfish.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

14 mg/L

Additional information

In order to evaluate the effect of cloquintocet-mexyl to fish, five acute toxicity tests with four freshwater species were conducted. The fish were exposed to 5 or 6 concentrations at a temperature of 12-14°C (rainbow trout) or 22-23°C (bluegill, carp, and catfish). The pH values were between 7.8 and 8.5 in all five studies. The results are summarized in the table below and are expressed as initial measured and mean measured concentrations (Rufli 1988, Rufli 1988, Rufli 1988, Rufli 1989).The 96-h LC50 of cloquintocet-mexyl to fish ranged from 14 to >133 mg/L, depending on the species.

In a second study (Palmer and Krueger, 1998), rainbow trout (Oncorhynchus mykiss) were exposed to cloquintocet-mexyl at nominal concentrations of 0.045, 0.097, 0.19, 0.38 and 0.97 mg/L, in a flow-through test for 96 hours. The 96-hour LC₅₀for rainbow trout was > 0.97 mg/L, the highest (measured) concentration tested. The no observed effect concentration was 0.97 mg/L.

In addition, the prolonged short-term toxicity of cloquintocet-mexyl 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. The overall 21-day NOEC of cloquintocet-mexyl to juvenileOncorhynchus mykissunder 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 cloquintocet-mexyl/L (nominal), respectively.

 

Table A. Acute toxicity of cloquintocet-mexyl to fish

Species	Test conditions	96h-LC50^(a)[mg/L]	NOEC [mg/L]	LC100 [mg/L]	Reference
Oncorhynchus mykiss (Rainbow trout)	Static	>76 / >63.8	7.4 / 4.8	>76 / >63.8	Rufli (1988)
Oncorhynchus mykiss (Rainbow trout)	Flow-through Freshwater	> 0.97^(b)	0.97^(b)	> 0.97^(b)	Palmer and Krueger (1998)
Lepomis macrochirus (Bluegill sunfish)	Static	>51 / >38	17 / 12.4	>51 / >38	Rufli (1988)
Cyprinus carpio (Carp)	Semi static	>133 / >100	133 / 104	>133 / >104	Rufli (1988)
Ictalurus punctatus (Channel catfish)	Semi static	14^(c)	1.79 / 1.32	>28.3 / >27.4	Rufli (1989)

(a) based on: [initial measured concentration] / [mean measured concentration]; (b) the highest mean measured concentration tested in this study, no effect at this concentration; (c) based on end measured concentration

Additionally, there are four studies available (Grade 1992, Grade 1992, Grade 1992 and Grade 1992) investigating the toxicity of a metabolite of cloquintocet-mexyl, CGA153433 (i.e. [(5-chloroquinolin-8-yl)oxy]acetic acid). The lowest LC50 and NOEC values were obtained for Lepomis macrochirus, with 82.6 mg/L and 8.3 mg/L respectively. All studies were GLP-compliant and conducted to OECD 203 guideline. They are considered to be reliable without restrictions, with the exception of the study of the toxicity of the metabolite CGA153433 to bluegill (Lepomis macrochinus) (Grade, 1992), which is reliable with restrictions. The results are summarized in the table below and were expressed as nominal concentrations except for bluegill sunfish where results were based on mean measured concentrations.

 

Table B. Acute toxicity of CGA153433 to fish

Test substance	Species	Test conditions	96h-LC50 [mg/L]	NOEC [mg/L]	LC100 [mg/L]	Reference
CGA153433	Oncorhynchus mykiss (Rainbow trout)	Static	89	18	> 100	Grade (1992)
	Lepomis macrochirus (Bluegill sunfish)	Static	82.6	8.3	> 76.1	Grade (1992)
	Cyprinus carpio (Common carp)	Static	90	58	> 100	Grade (1992)
	Ictalurus punctatus (Channel catfish)	Static	> 100	³100	> 100	Grade (1992)

The key value used in the chemical safety assessment for cloquintocet-mexyl is the 96h LC50 of 14 mg/l for channel catfish (Ictalurus punctatus) (Rufli, 1992) which represents the lowest value for this endpoint (remark: It is recognised that the Vial (1990) OECD 204 prolonged study reports a lower LC50 than this, but this is for extended exposure (21 days, compared to 96 hours) and therefore cannot be considered to represent a standard acute endpoint.). It should be noted that the LC50 reported in this study is based on values measured at the end of the study (96h), and is therefore conservative compared to taking a mean value over the duration of the study. In the case of the metabolite CGA153433, the lowest reported 96h LC50 is 82.6 mg/L (mean measured) for Bluegill sunfish (Lepomis macrochirus).