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

Toxicity to aquatic algae and cyanobacteria

Description of key information

Three algal studies have been conducted and are presented below:

 

The first study determined the effects of XDE-558 (cloquintocet-acid) on the growth of the unicellular freshwater green alga Pseudokirchneriella subcapitata. The study was carried out according to OECD guideline 201 and EPA guideline OPPTS 850.5400. Pseudokirchneriella subcapitata cells were exposed to XDE-558 (cloquintocet-acid) for 96 hours under static conditions. Nominal concentrations were 0 (control) 0.4, 1.2, 3.7, 11, 33 and 100 mg/L, the corresponding arithmetic mean measured concentrations were 0, 0.457, 1.39, 4.35, 12.7, 38.3 and 123 mg/L after 72 hours and 0, 0.439, 1.35, 4.34, 12.6, 38.4 and 125 mg/L, respectively, after 96 hours. A six day recovery phase was performed with the 100 mg/L treatment; growth was seen at the end of the six day period therefore XDE-558 can be considered to be algistatic at 100 mg/L.

 

Based on arithmetic mean concentrations the following results were obtained:

Biomass – 72h IbC50- 46.7 mg/L, 96 h IbC50– 34.2 mg/L

Growth rate - 72h IrC50– 67.1 mg/L, 96 h IrC50– 44.1 mg/L

Yield - 72h IyC50– 43.8 mg/L, 96 h IyC50– 32.4 mg/L

The overall NOEC was 12.6 mg/L

 

 

The second study determined the effects of XDE-558 (cloquintocet-acid) on the growth of the cyanobacterium Anabaena flos-aquae. The study was carried out according to OECD guideline 201 and EPA guideline OPPTS 850.4550. Anabaena flos-aquae cells were exposed to XDE-558 (cloquintocet-acid) for 96 hours under static conditions. Nominal concentrations were 0 (control) 0.19, 0.57, 1.7, 5.0, 15 and 45 mg/L, corresponding arithmetic mean measured concentrations were 0, 0.208, 0.603, 1.81, 5.33, 16.4 and 49.9 mg/L after 72 hours and 0, 0.206, 0.603, 1.81, 5.31, 16.4 and 50.0 mg/L, respectively, after 96 hours.

 

Based on arithmetic mean concentrations the following results were obtained:

Biomass – 72h IbC50– 16.3 mg/L, 96 h IbC50– 13.9 mg/L

Growth rate - 72h IbC50– 23.7 mg/L, 96 h IbC50– 25.9 mg/L

Yield - 72h IbC50– 16.1 mg/L, 96 h IbC50– 11.4 mg/L

The overall NOEC was 1.81 mg/L

 

 

The third study determined the effects of XDE-558 (cloquintocet-acid) on the growth of the marine diatom Skeletonema costatum. The study was carried out according to EPA guideline OCSPP 850.4500. Skeletonema costatum cells were exposed to XDE-558 (cloquintocet-acid) for 96 hours under static conditions. Nominal concentrations were 0 (control) 0.073, 0.22, 0.67, 2.0, 6.0 and 18 mg/L, the corresponding arithmetic mean measured concentrations were 0, 0.546, 0.237, 0.686, 2.24, 7.08 and 20.4 mg/L, respectively, after 96 hours. A nine day recovery phase was performed with the nominal 18 mg/L treatment, no growth was seen at the end of the nine day period therefore XDE-558 can be considered to be algicidal at 18 mg/L.

 

Based on arithmetic mean concentrations the following results were obtained:

Biomass – 96 h IbC50– 8.82 mg/L

Growth rate - 96 h IrC50– 12.5 mg/L

Yield - 72h IbC50- 96 h IyC50– 8.21 mg/L

The overall NOEC was 2.24 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

32.4 mg/L

EC50 for marine water algae:

8.21 mg/L

EC10 or NOEC for freshwater algae:

12.6 mg/L

EC10 or NOEC for marine water algae:

2.24 mg/L