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Diss Factsheets

Ecotoxicological information

Toxicity to microorganisms

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Administrative data

Link to relevant study record(s)

toxicity to microorganisms, other
non-standard batch extant respirometric assay
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non guideline study described in sufficient detail.
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
Autotrophic growth inferred from oxygen uptake rates due to ammonia oxidation measured in triplicate using a batch extant respirometric assay.
GLP compliance:
not specified
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable
Analytical monitoring:
Details on sampling:
Not applicable
not specified
Details on test solutions:
No data reported
Test organisms (species):
other: Mixed and enriched nitrifying bacteria - laboratory cultured
Details on inoculum:
Preparation of inoculum: Mixed liquor periodically removed from tank reactor used for batch respirometric studies. Method of cultivation: Continuously stirred tank reactor operating at solids retention time of 20 days and hydralic retention time of 1 day. Original seed from nitrifying activated sludge plant in Missouri, USA. Sole energy source supplied as ammonium (8.3 mM, NH4NO3). Filtered laboratory air used to ensure adequate mixing and aeration. pH Maintained at 7.5 ± 0.1 by addition of 0.5 M sodium carbonate. Micro and micronutrient media as follows (all in mg/L): Mg(NO3)2 61, Ca(NO3)2 41, NaNO3 879, NH4NO3 667, K2HPO4 3.9, FeCl2.4H2O 2.0, MnSO4.H20 3.4, (NH4)6Mo7O24.4H20 1.2, CuSO4 0.8, Zn(NO3)2.6H20 1.8, Ni(NO3)2.6H20 0.3.
Test type:
Water media type:
Limit test:
Total exposure duration:
13.33 min
Remarks on exposure duration:
Reported as 800 seconds
Post exposure observation period:
No data reported
Test temperature:
25 ± 2°C
7.5 (buffered with MOPS)
Dissolved oxygen:
No data reported
Not applicable
Nominal and measured concentrations:
Nominal: 0 (control),0.05, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0 mg Ag/L
Details on test conditions:
50 mL test vessel. Exposure medium as per culture. Three replicates per concentration. Biomass loading not reported.
Reference substance (positive control):
not specified
13.3 min
Dose descriptor:
Effect conc.:
0.05 other: mg Ag/L
Remarks on result:
other: ~10-15% inhibition
13.3 min
Dose descriptor:
Effect conc.:
0.025 other: mg Ag/L
Remarks on result:
other: calculated as LOEC/2
Details on results:
Results based on nominal concentrations.
Results with reference substance (positive control):
Not applicable
Reported statistics and error estimates:
No data reported
Validity criteria fulfilled:
not applicable
NOEC for inhibition of autotrophic nitrification by AgNO3 was determined to be 0.025 mg Ag/L.
Executive summary:

In a non-standard batch extant respirometric assay the NOEC for inhibition of autotrophic nitrification by AgNO3 was determined to be 0.025 mg Ag/L.

Description of key information

The NOEC for inhibition of nitrification is 0.025 mg Ag/L.

Key value for chemical safety assessment

Additional information

The PNECmicroorganisms is intended to protect the degradation functions and process performance and efficiency of domestic and industrial sewage treatment plants (STP). ECHA guidance (ECHA 2008) allows the derivation of a PNECmicroorganisms from a wide range of laboratory tests utilising microorganisms, including standardised biodegradation tests, respiration inhibition tests, activated sludge growth inhibition tests, pilot scale activated sludge simulation tests and tests performed with specific bacterial populations, such as nitrifying bacteria or ciliates. Data on the toxicity of silver in Microtox assays (e.g. Hsieh et al. 2004) are not considered relevant to STP functioning. Nitrifying bacteria are considered to be the most sensitive component of the microbial fauna found in STP and tests investigating effects on these fauna are preferred to more generic microbial testing when deriving a PNECmicroorganisms. An AF of 1 is applied to NOECs from these types of tests when deriving a PNECmicroorganisms (the AF for other microbial tests range from 10 – 100).

Two studies (Choi et al. 2008, Choi and Hu 2008) report the effects of ionic silver on nitrification inhibition. Additional methodological information was obtained for both of these studies from Hu et al. (2002). Both studies used a population of nitrifying bacteria initially obtained from a municipal STP (Missouri, USA) and each reports inhibition of nitrification of between 10 and 20% at the lowest test concentration (LOEC) of silver tested. Where a LOEC is associated with effects >10% but <20% ECHA guidance (ECHA 2008) allows a NOEC to be calculated as LOEC/2. This results in NOECs of 0.025 and 0.05 mg/L for Choi et al (2008) and Choi and Hu (2008), respectively.