Silver chloride

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Remarks:

non-standard batch extant respirometric assay

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

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:

no

Details on sampling:

Not applicable

Vehicle:

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:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

13.33 min

Remarks on exposure duration:

Reported as 800 seconds

Post exposure observation period:

None

Hardness:

No data reported

Test temperature:

25 ± 2°C

pH:

7.5 (buffered with MOPS)

Dissolved oxygen:

No data reported

Salinity:

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

Duration:

13.3 min

Dose descriptor:

LOEC

Effect conc.:

0.05 other: mg Ag/L

Remarks on result:

other: ~10-15% inhibition

Duration:

13.3 min

Dose descriptor:

NOEC

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

Conclusions:

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.

Additional information

The PNEC_{microorganisms} 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 PNEC_{microorganisms} 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 PNEC_{microorganisms}. An AF of 1 is applied to NOECs from these types of tests when deriving a PNEC_{microorganisms} (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.