2-Naphthalenesulfonic acid, 4-hydroxy-3-[2-[2-methoxy-5-[[2-(sulfooxy)ethyl]sulfonyl]phenyl]diazenyl]-7-[(sulfomethyl)amino]-8-[2-[2-sulfo-4-[[2-(sulfooxy)ethyl]sulfonyl]phenyl]diazenyl]-, sodium salt (1:5)

Toxicity to aquatic algae and cyanobacteria

Description of key information

The inhibition of growth observed in this study seemed to be caused by light absorption only.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

A modified algal inhibition test was performed to evaluate the toxicity of the test substance on alga, Desmodesmus subspicatus, according to the EU Method C.3, which is equivalent to OECD guideline 201, in compliance with GLP. The modified test design consisted of three different parts. Part I was mostly similar to the test design of an algal test according to the method described in EU method C.3. In Part II, the algae were treated as controls but the light conditions to which the algae were exposed corresponded to the light conditions of the algae within the test media of Part I. To comply with those light conditions the light energy was led through glass vessels containing the same concentration levels as used in Part I, however without algae. Thus, the growth inhibition measured in Part II was caused by light absorption (algaestatic effect) only. Part III of the modified test system was the control consisting of six replicates. Exponentially growing algal cells were exposed to test substance dissolved in water (Part I), for a period of 72 h to a range of concentrations, nominally 0.9, 1.9, 4.3, 9.4, 20.7, 45.5 and 100 mg/L. Cell densities were recorded at 24 h intervals. The 72 h EC50 (based on both, growth [b] and growth rate (r), was calculated or read from the concentration/percentage response curve. During the test a temperature range of 21-25°C was maintained in the test vessels. The statistical evaluation steps were performed for both parts of the study.

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth (indexb)and growth rate (indexr),relative to control cultures grown under identical conditions. Growth and growth rates were used to calculate a No Observed Effect Concentration and a Lowest Observed Effect Concentration according to DUNNETT (1955, 1964). The following values were determined:

	Results [mg/L]:
	PART I	PART II
EbC 50 (0-72 h)	10.3	8.2
95% confidence limits	7.6 — 13.9	4.4 —14.9
ErC 50 (0-72 h)	41.8	64.6
95% confidence limits	36.4 — 48.5	37.4 — 200.2
NOEC [b]	4.3	1.9
LOEC [b]	9.4	4.3
NOEC [r]	4.3	4.3
LOEC [r]	9.4	9.4

 

All results are expressed in terms of nominal concentrations. Recovery rates ranged from 98.6 - 135.2% of nominal values at 0 hours, and from 92.6 - 103.3% of nominal values at 72 hours.

A comparison of the results for the parameter "percentage inhibition of the growth rate" gained in PART Iand II of the study, results only for the test concentration level 9.4 mg/L and the two highest concentration levels in differences exceeding 10%. The observed percentage differences of 10.6% and 14.6% observed for the two highest test concentrations only slightly exceeded the 10% level. Due to the increasing growth inhibition in the highest dose levels only low cell numbers are the basis for growth rate calculations. A higher variation of growth rates at this concentration levels has therefore to be expected. At the concentration level of 9.4 mg/L the inhibition of algae growth determined in Part II was stronger than the one detected in PART I indicating no algaecide effects. Therefore, the inhibition of growth observed in this study seemed to be caused by light absorption only.

The results are expressed in terms of nominal concentrations.