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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

A 14-day LC50 value of 19 mg/l (nominal concentration) in unbuffered media, and a 14 day LC50 value of >100 mg/l (nominal concentration) (highest concentration tested) in buffered media have been determined for the effects of cyclohexylamine on mortality of Oryzias latipes.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
100 mg/L

Additional information

A 14-day LC50 value of 19 mg/l (nominal concentration) in unbuffered media, and a 14-day LC50 value of >100 mg/l (nominal concentration) (highest concentration tested) in buffered media have been determined for the effects of cyclohexylamine on mortality of Oryzias latipes in compliance with OECD Test Guideline 204 (Fish, Prolonged Toxicity Test: 14-day Study) (data from ECHA registration dossier, review article or handbook, MITI 1997).

In the unbuffered media, the pH increased from 7.5 (1.9 mg/L, 0 h) up to 9.8 (30 mg/L, 0 h). All fish were dead after 2 days in the highest concentration level.

In the buffered test solutions, the pH ranged between 6.8 and 7.3 for all concentration levels. No adverse effects were observed in these solutions.

The amine component of the test substance is basic and can therefore significantly increase the pH of the test media. The limited amount of test solution used in aquatic tests may not be adequate to act as a buffer to prevent large pH rises. High pH resulting from the addition of an amine substance to test solutions can cause intolerable conditions for aquatic organisms, therefore effects occurring at high pH cannot necessarily be attributed to the toxicity of the test substance. In addition, the un-ionised form of the amine is more toxic than the ionised form and there is more of the un-ionised form present at higher pH. This means the toxicity of the amine could vary according to the pH of the environment. For environmental waters having a pH closer to 7 it is likely that the results of ecotoxicity studies with amines overestimate toxicity (i.e. the value of E(L)C50 may possibly be higher under pH-neutral conditions). It is therefore important that test solutions with amine substances are buffered, to ensure that effects observed (if any) can be attributed to the toxicity of the test substance and are not a result of increases of pH.

Because the pH rose significantly in the unbuffered test media, the result determined in the test with buffered test media can be considered more reliable and is therefore selected as key.

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