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Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Description of key information

Waiving

Additional information

The test material is a dark color dye which when mixed in test medium will impart dark color. Due to light absorption, colored substances such as dyes can inhibit algal growth, which is not the result of a toxic action. This shading effect can confound measures of chemical toxicity and thus impair the risk assessment. In an effort to avoid this problem Lemna gibba (Duckweed) Growth Inhibition test (Static) is conducted.

Due to a previous test conducted on another dye (Acid Black 210 Sodium Salt), the test conducted on the Alge reported an EC50 at 72 hours based on the growth rate of 13.7 mg/l, otherwise a more recent test contucted with a different salification of the same core structure (Acid Black 210 - Potassium Salt) on the aquatic plants Lemna minor showed a NOEC > 1 mg/l and an EC50 between 10 and 100 mg/l.

The observed algae toxicity is reasonably not referred to the counter ion but is due to the shadowing effect of the substance in the tested medium. Several studies on algae conducted on dark dyes, including those with a modified test system for coloured substances, showed that the growth inhibition is not due to a toxic effect of the dye, but to the light absorption of the stained water.

 

Lemna is an aquatic plant that develops his leaves on the surface of the water, while nourishing substances are taken from the water solution. With this test the observed effect is only related to the potential toxicity of the substance and not to the potential shading effect of an Alga study. A deviation to the protocol has been applied to the test recommended for dyes (Michael Cleuvers, 2002), i.e. beakers will be incubated on a black non-reflecting surface; additionally, the walls of the incubation chambers will also be covered with black fabric in order to avoid reflection.

According to the ECHA Guidance R7.b, Table R.7.8 - 3 Summary of difficult substance testing issues, if the substance is coloured, the absorption of light at relevant wavelengths may cause an indirect effect on aquatic plant growth by inhibiting photosynthesis, the 7-d Lemna growth test avoids the problem since the fronds grow at the water surface.

Based on these information, the 7-d Lemna growth test was conducted instead of the Short-term toxicity to algae.