Sodium 4-[(5-amino-3-methyl-1-phenyl-1H-pyrazol-4-yl)azo]-2,5-dichlorobenzenesulphonate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Not toxic to aquatic algae and cyanobacteria.

Additional information

There are no data on toxicity of Acid Yellow 049 sodium salt to algae and cyanobacteria, thus a read across approach was followed.

Available data on structural analogues, i.e. Similar Substance 02 and Acid Yellow 049 (acid), were taken into account. Details on the read across approach are reported in section 13.

In the key study (2015), Similar Substance 02 was tested for growth inhibition on algae Pseudokirchneriella subcapitata, according to the OECD guideline 201. Following preliminary range-finding tests, algae was exposed to an aqueous solution of the test item at concentration of 1.0, 3.2, 10, 32 and 100 mg/l (three replicates per concentration), over a period of 72 hours.

Growth rate (r) and yield (y) of algae were not significantly affected by the presence of the test item over the 72 -hour exposure period.

There were no statistically significant decreases in growth rate and/or yield, between control and test concentrations up to 32 mg/l. Accordingly, NOEC was 32 mg/l and LOEC was 100 mg/l, for both growth rate and yield.

Analysis of the test preparations at 0 and 72 hours showed measured concentrations between 88 % and 106 % of nominal, thus results were only based on nominal concentrations.

In additon, a study on Acid Yellow 049 (acid) was available (1994). Growth inhibition on algae Desmodesmus subspicatus was tested according to ISO 8692. A 72-hour test was conducted at concentration of 1000, 900, 850, 800, 750 ml/l, diluting a stock solution of 500 mg/l. Effects were recorded after 72 hours in terms of biomass: EbC5 of 11.1 mg/l (nominal) and EbC50 of 31.6 mg/l (nominal).

Even if there was no information about measured concentrations, there were no reasons to suspect that the substance might be unstable over the whole testing period, based on its physicochemical properties: it is water soluble, not readily abiotically or biotically degradable. Possible adsorption is expected to be negligible.

In the endpoint evaluation, the study from 1994 was disregarded. Indeed, although the test procedure is in accordance with generally accepted scientific standards, details on test results are not complete and do not permit to draw a conclusion on the specific endpoint. Unfortunately, only the values related to the effects on biomass are reported. The original study report is no more available, thus no further details can be retrieved.

According to the third version of the ECHA guidance R.7b, the preferred observational endpoint in the algal test is the growth rate inhibition because it is not dependent on the test design.

In the guideline, it is indicated that when both acute growth rate and biomass EC values are reported, the latter should not be used because direct use of the biomass concentration without logarithmic transformation cannot be applied to an analysis of results from a system in exponential growth. Where only the EbC is reported, but primary data are available, a re-analysis of the data should therefore be carried out to determine the ErC. If only an EbC is reported and no primary data are available, it should be considered to perform a new algae study to obtain a valid ErC / NOEC value, especially if algae are the most relevant species for the effects assessment.

It should be noted that specific growth rate is a logarithmic term and small changes in growth rate may lead to great changes in biomass, thus, in many cases, the EbC values result to be numerically lower than ErC ones. Based on the magnitude of the EbC50 value recorded in the experiment, the substance is not expected to be toxic to algae and cyanobacteria, thus a new test can be considered as not necessary. Furthermore, this expectation is supported by results on Similar Substance 02.

Another aspect that should be considered is that coloured substances are often assumed to affect algal growth due to shading of the algae. Coloured substances can absorb photosynthetically active light and hence limit growth of algal cultures. Absorption will be proportional to test substance concentration and it may lead to effects which may likely be confused with inherent toxicity. Several studies on algae exposed to coloured dyes showed that the effects are mainly correlated to the reduced light absorption, caused by the stained water and not due to an effective toxicity of the dye. In the case of Acid Yellow 049, the possible impact of the colouration can be considered as low, but it cannot be completely excluded.

REFERENCE

ECHA (2016). Guidance on Information Requirements and Chemical Safety Assessment. Chapter R.7b: endpoint specific guidance. Version 3.0. February 2016.