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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Two reliable acute/chronic toxicity studies (Klimisch 1, GLP) for  the algal species Pseudokirchneriella subcapitata are available. The studies have been conducted with two different batches of aluminium potassium fluoride: Nocolok Flux and Hot melt PAF. The 72-h EC50 values for growth rate were33.5 and 12.7 mg/l (corresponding to 17.4 and 7.0 mg F/L), respectively. The 72 hr NOErC values were reported to be 11 and 4.3 mg/l (corresponding to 5.7 and 2.4 mg F/L), respectively. The lowest values, ErC50 of 12.7 mg/l and NOErC of 4.3 mg/l will be used in the assessment.    

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Two reliable acute/chronic toxicity studies (Klimisch 1, GLP) for the algal species Pseudokirchneriella subcapitata are available (ECT Oekotoxikologie, 2012a and b). The studies have been conducted with two different batches of aluminium potassium fluoride: Nocolok Flux and Hot melt PAF. The 72-h EC50 values for growth rate were 33.5 and 12.7 mg/l, respectively. The 72 hr NOErC values were reported to be 11 and 4.3 mg/l, respectively. During the conductance of this study, special attention was given to the preparation of test solutions since it is known that the test substance can form precipitates with nutrient salts present in the algal medium. For this reason, two different medium types (Kuhl&Lorenzen-medium and modified OECD medium) have been tested in a pre-test and the medium with the highest recovery of the test substance was selected for the final test. Test solutions were analysed to determine actual levels of fluoride, calculated based on the fluoride content in the test item. The determinations of actual concentrations in the studies showed mean recoveries of 97.8% for Nocolok Flux and 73 - 96% for Hot melt PAF with a decline at higher concentrations. In addition, no precipitates were observed during the tests. For this reason, it was concluded that the results of both studies were suitable for hazard and risk assessment purposes. The lowest observed values, ErC50 of 12.7 mg/l and NOErC of 4.3 mg/l will be used in the assessment.

A previous study (Solvay Pharmaceuticals, 2010b) that has been conducted with aluminium potassium fluoride according to OECD 201 has been disregarded. In this study a 72-h EC50 value for growth rate of 8.2 mg/L was observed, based on measured concentrations, the 72-h NOErC was 1.6 mg/L. The results of this study with aluminium potassium fluoride are difficult to interpret. The dose-response showed a higher inhibition at higher concentrations. However, after 48 hours of exposure, a slight precipitation was observed at the two highest concentrations (11 and 25 mg/L). After 72 hours of exposure, green algae particles were observed at the two highest concentrations (11 and 25 mg/L). It is unknown what the precipitate consisted of since the concentration of aluminium potassium fluoride is based on the concentration fluoride in solution. The recovery of the test substance based on the actual levels of fluoride ranged between 26 and 35% which confirms a precipitation of the test substance with nutrient salts in the test medium. The precipitation of the aluminium potassium fluoride can influence the reliability of the cell density measurements and result in a reduced availability of salts and trace elements in the test medium. It was therefore concluded that the results of this test were not reliable due to the complexation of aluminium potassium fluoride in the test medium.