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Toxicity to microorganisms

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Description of key information

The key study for this endpoint (Clarke, 2010) was conducted under GLP conditions and to the OECD guideline 209 using ammonium zirconium carbonate as test material. The study reported a 3 hour NOEC of >1000 mg/l for sewage microorganisms collected from a predominantly domestic sewage treatment plant. The study was conducted at test concentrations of 10, 32, 100, 320 and 1000 mg/l.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

The toxicity of the test material to microorganisms is being addressed using a key study (Clarke, 2010) on a surrogate substance, using the read across argument based on its common ionic compounds. Toxicity to microorganisms was investigated in a GLP compliant study performed in accordance with the standardised guidelines using the surrogate substance ammonium zirconium carbonate. The study was performed to a good standard with a sufficient level of reporting to be assigned a reliability score of 2 according to the principles for assessing data quality set out in Klimisch (1997).

Information provided by the Sponsor indicated that at the pH and concentration used in this study the test item was likely to have become unstable. It is considered likely that the addition of the test item to water resulted in the rapid decomposition of the substance to form zirconium hydroxide, together with accompanying release of carbonate and ammonium ions to the solution. All concentrations have thus been given as nominal values.

The sewage sludge micro-organisms were exposed to the test material for 3 hours at the following concentrations: 10, 32, 100, 320 and 1000 mg/l. The sample was maintained in continuous aeration in the laboratory under constant conditions. After the 3 hour exposure time, samples were removed and placed in a BOD bottle and the rate of respiration was measured over the linear portion of the oxygen consumption trace. The inhibitory effect as a result of exposure was also calculated as percentage inhibition, this was plotted against concentration for the reference item only and a line fitted using the Xlfit software package. The EC₁₅, EC₂₀, EC₅₀ and EC₈₀ values determined from the equation for the fitted line.

The effect of the test item on the respiration of activated sewage sludge micro-organisms gave a 3-Hour EC₅₀ of greater than 1000 mg/l. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 1000 mg/l.

Key value for chemical safety assessment

NOEC: 1000 mg/l