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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Acutely very toxic to aquatic algae.

Key value for chemical safety assessment

Additional information

The growth inhibition on algae has been examined in a 72 -hour static GLP guideline study according to ISO 10253 [Knoll MicroCheck 1998 (a)] with the saltwater species Skeletonema costatum. Additionally, algistatic and algicidal effects were investigated according to US EPA OPPTS 850.5400 "Algal Toxicity", Tiers I and II. At test termination for the growth inhibition examination, an ErC50 = 0.25 mg/L (nominal) and a NOEC = 0.08 mg/L (nominal) could be determined. Algistatic effects were seen at 0.42 mg/L (nominal) and algicidal effects were observed at 1.0 mg/L (nominal).

The toxicity of bronopol to freshwater algae species has been investigated in an OECD 201 guideline study with Selenastrum capricornutum as test organism [Boots Microcheck 1994]. After the exposure period of 72 h an ErC50 of 0.37 mg/L and a NOErC of 0.1 mg/L was determined.

Further on, two growth inhibition tests on algae were carried out according to OECD guideline 201 [Boots Microcheck 1994] with two different freshwater algae species. The 72 -hour ErC50 was determined to be in the range of 0.89 to 2.84 mg/L for Chlorella vulgaris and > 1.00 mg/L for Scenedesmus subspicatus. The NOErCs were determined to be 0.32 and 0.10 mg/L for Chlorella vulgaris and Scenedesmus subspicatus, respectively. All results refer to nominal concentrations since no clear quantification of the actual exposure concentrations could be achieved. The inconsistent results obtained by analytical monitoring may be related to the fact that Bronopol rapidly hydrolyses at pH values ranging from 7 to 9.

Additionally an algae growth inhibition study with Scenedesmus subspicatus was conducted according to OECD guideline 201 [Knoll MicroCheck 1998 (b)]. Additionally, algistatic and algicidal effects were investigated according to US EPA OPPTS 850.5400 "Algal Toxicity", Tiers I and II. At test termination after 72 h, the ErC50 for Bronopol was determined to be 0.67 mg/L (nominal) and the NOErC was determined to be 0.1 mg/L (nominal). An algicidal effect of Bronopol after 7 days was indicated at 3.2 mg/L and higher test concentrations.

The acute and chronic results obtained from these studies were similar to the ones retrieved from the key study and can therefore be used as supporting evidence of the acute toxicity of Bronopol to aquatic algae.