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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The inhibition of the algal population of Ramatroban butylammonium salt was measured as reduction in growth rate (index r) for a period of 72 hours in a range of concentrations, nominally 6.3, 12.5, 25, 50 and 100 mg/L. An ErC10 of 35.2 mg/L, an ErC50 of >100 mg/L, a NOEC [r] of 25 mg/L and a LOEC [r] of 50 mg/L were determined.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
25 mg/L

Additional information

In order to test acute toxicity to algae of Ramatroban butylammonium salt, Desmodesmus subspicatus was exposed to the test solution of five nominal concentrations (6.3, 12.5, 25, 50 and 100 mg/L) and blank control solution for a period of 72 hours under static conditions. The study was conducted in accordance with Commission Regulation (EC) No 761/2009 amending Regulation No 440/2008, Method C.3 `Freshwater Alga and Cyanobacteria, Growth inhibition test¿ (2009) which is equivalent to OECD Guideline for Testing of Chemicals No. 201 'Alga, Growth Inhibition Test' (2006).

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions.The measured concentrations confirmed that deviation from the nominal concentrations was less than 30 % ( measured concentrations were in the range of 89.9 - 92.4 % of the nominal concentrations.)

The following results were calculated:

ErC 50 (0-72 h): > 100 mg/L

ErC 10 (0-72 h): 35.2 mg/L

NOEC [r] (t¿ 0.05): 25 mg/L

LOEC [r] (t¿ 0.05): 50 mg/L

Comments:As pointed out, in this study the NOEC/LOEC (72 h) determination by statistical methods for growth rate does not appear to be meaningful. For growth rate (72 h) the statistical NOEC and LOEC values are 12.5 mg/L and 25 mg/L respectively. In this cases an effect of 6.3 % inhibition was determined as LOEC value, whereas from the biological point of view the result of only 6.3 % inhibition shows no biological effect. This is corroborated by various algal test guidelines (e.g. DIN 38 412 part 33) which consider only effects > 10 % as biologically relevant. In line with many regulatory-type decisions within the Existing Chemicals Programme of the EU, the EC10 values are generally regarded as surrogates for the NOEC. In the present case for growth rate 10 % effect is effectuated by a concentration of ¿ 25 mg/L, so this value should be taken forward as a NOEC.

This toxicity study is classified as acceptable and satisfies the guideline requirements for the acute algae study.