Chlorhexidine

Endpoint summary

Additional information

The toxicity of Chlorhexidine base or Chlorhexidine digluconate to aquatic organisms was tested in several studies covering different trophic levels. When Chlorhexidine digluconate was used as test substance, actually Chlorhexidine base was the active component, therefore the results can be converted to equivalents of Chlorhexidine base. All tests were performed according to the OECD Guidelines.

In a study on the acute toxicity of Chlorhexidine base towards fish the LC₅₀was determined to be 1.4 mg/L, employing the zebrafish (Brachydanio rerio) as the test organism.

Acute toxicity towards the water flea Daphnia magna was tested using Chlorhexidine digluconate as test substance. The EC₅₀was established at 0.087 mg a.s./L, corresponding to 0.049 mg Chlorhexidine base/L.

Algal toxicity was found to be higher with an EC₅₀value of 0.081 mg Chlorhexidine digluconate/L and an EC₁₀of 0.030 mg Chlorhexidine digluconate/L, both values related to growth rate. The corresponding concentrations are EC₅₀= 0.046 mg Chlorhexidine base/L and EC₁₀= 0.017 mg Chlorhexidine base/L.

The substance concentration in the medium during the fish test was not measured during the study. However, results from the daphnia test reveal that the test substance concentration was stable over the test period of 48 hours. Therefore, it can be assumed that also during the fish test the test substance concentration was stable under the semistatic conditions with daily renewal of the medium. Measurements during the algae test revealed stability of the test item over 72 hours.

A test on reproduction of Daphnia magna was performed according to the OECD Guideline 211 A, using Chlorhexidine digluconate as test substance. The NOEC for all examined endpoints was found to be 0.02 mg Chlorhexidine digluconate/L, corresponding to 0.012 mg Chlorhexidine base/L.

A study on chronic fish toxicity is not available. However, the available data on acute toxicity indicate that fish is the trophic level with the lowest sensitivity, as the LC₅₀(1.4 mg/L, Brachydanio rerio) is by a factor of >20 higher compared to the EC₅₀of 0.049 mg/L of Daphnia magna and the E_rC₅₀of 0.046 mg/L of the algae (Desmodesmus subspicatus). Therefore, it is unlikely that a chronic NOEC from fish would be lower than the NOECs available for the more sensitive taxonomic groups – invertebrates and algae. Furthermore, if avoidable, testing of vertebrates would be ethically questionable and contrary to animal welfare concerns.

The acute toxicity of Chlorhexidine digluconate towards bacteria was tested according to the OECD Guideline 209, by determining the inhibition of respiration of activated sludge. The EC₅₀was established to be 25 mg Chlorhexidine digluconate/L, corresponding to 14 mg Chlorhexidine base/L.