Ethyltriphenylphosphonium iodide

Toxicity to aquatic algae and cyanobacteria

Description of key information

48h-ErC50 and NOEC for green algae (Pseudokirchneriella subcapitata): 18 mg/L and 1.69 mg/L, respectively (OECD201/EU C.3, GLP, read across from structural analogue)

Key value for chemical safety assessment

EC50 for freshwater algae:

18 mg/L

EC10 or NOEC for freshwater algae:

1.69 mg/L

Additional information

The read-across hypothesis is based on the assumption that source and target do have comparable toxicity to aquatic algae. Source and target are both Ethyltriphenylphosphonium salts with an identical organic moiety, the Ethyltriphenylphosphonium-ion. Source and target deviate only in their counterions - the source substance has bromide as counter ion, the target substance iodide. However, source substance as well as target substance are soluble in water. When disolved, the organic moiety and the counter ions act individually. The counter ions bromide and iodide are not associated with toxicity to aquatic algae leading to classification. Thus, intrinsic toxicity to aquatic algae is determined by the organic moiety only. As source and target do have an identical organic moiety, this read across is justified.

The 48-hr-acute toxicity of source Ethyltriphenylfosfonium bromide to Pseudokirchneriella subcapitata was studied under static conditions according to OECD Guideline 201 (adopted March 23, 2006), EU Method C.3 (December 1992) and ISO International Standard 8692 (October 2004). Exponentially growing cultures were exposed to a control and Ethyltriphenylfosfonium bromide concentrations of 0.60, 1.5, 3.8, 9.5, 24 and 60 mg/L. Test concentrations were based on the result of a preceding range-finding test. The total test period was 48 hours and the initial algal cell density was 104 cells/mL. Samples for determination of actual exposure concentrations were taken at the start, after 24 and 48 hours of exposure. Analyses showed that measured concentrations were in agreement with nominal throughout the 48-hour test period (97-104%).

Ethyltriphenylfosfonium bromide reduced growth rate and inhibited the yield of this fresh water algae species significantly at 3.8 mg/L and higher.

The EC50 for growth rate reduction (ErC50: 0-48h) was 16 mg/L with a 95 % confidence interval ranging from 9.8 to 25 mg/L.

The EC50 for yield inhibition (EyC50: 0-48h) was 4.3 mg/L with a 95 % confidence interval ranging from 3.1 to 6.1 mg/L.

The NOEC for both growth rate reduction and yield inhibition was 1.5 mg/L.

ErC50 Ethyltriphenylphosphonium iodide: 18 mg/L, recalculated from effect concentration of source substance in consideration of different molecular weights

NOEC Ethyltriphenylphosphonium iodide: 1.69 mg/L, recalculated from effect concentration of source substance in consideration of different molecular weights