1-[2-(allyloxy)ethyl-2-(2,4-dichlorophenyl)-1H-imidazolium hydrogen sulphate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Data from the related substance imazalil base is used to cover this endpoint. The justification for read across is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

16 d

Dose descriptor:

NOEC

Effect conc.:

133 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not indicated

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

according to guideline

Guideline:

other: Soap and Detergent Association, Test Procedure and Standards, ABS and LAS Biodegradability, J. 1M. Oil Chemists Soc. 42: 986-993

Qualifier:

according to guideline

Guideline:

other: Standard Methods for the examination of water and waste water, 13th Ed., 1971, APHA, AWWA & WPCF, New York

Principles of method if other than guideline:

- Principle of test:
The aim of the present study is to determine if imazalil is capable of disturbing the operation of a sewage treatment plant. For that purpose, a semi-continuous activated sludge metabolism study was carried out with imazalil following the Standard Method of the Soap and Detergent Association.

GLP compliance:

not specified

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The method involves the daily addition of fresh synthetic sewage (1l) containing the test compound, to activated sludge (0.5l). The synthetic sewage was prepared daily. In order to acclimatize the sludge, imazalil concentration was gradually increased from 0.10 to 100.0 ppm imazalil, in a period of 9 days. The treatment with the final concentration 100.0 ppm was repeated four times.

- Composition of synthetic sewage (pro litre):
* 8.50 mg KH2PO4
* 21.75 mg K2HPO4
* 33.40 mg Na2HPO4.2H2O
* 1.70 mg NH4Cl
* 22.50 mg MgSO4.7H2O
* 27.50 mg CaCl2
* 0.25 mg FeCl3.6H2O
* 300.00 mg peptone
* 200.00 mg beef extract
* 70.00 mg urea

Test organisms (species):

activated sludge

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

16 d

Hardness:

not indicated

Test temperature:

not indicated

pH:

not indicated

Dissolved oxygen:

not indicated

Salinity:

not applicable

Conductivity:

not applicable

Nominal and measured concentrations:

not applicable

Details on test conditions:

TEST SYSTEM
The method involves the daily addition of fresh synthetic sewage (1l) containing the test compound, to activated sludge (0.5l). The obtained mixture is aerated for 23 hours in a closed system; afterwards the sludge is allowed to settle for 30 minutes and then the supernatant (1l) is removed from the sludge unit. Fresh synthetic sewage and test compound are added again to the remaining sludge and the cycle is repeated.
The sludge unit was dosed daily with the synthetic sewage containing increasing concentrations of imazalil for 16 consecutive days. Dosing started at 0.10 ppm imazalil and increased up to 100.0 ppm.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Sewage COD reduction: Before each adding of the new synthetic sewage to the sludge unit, a small sample of the solution (about 5 ml) was taken for COD analysis (COD initial). At the end of each cycle, when sludge was completely settled, 1l of supernatant was removed and investigated for COD (COD final). The daily COD reduction is expressed as a difference between these two values.
- CO2-production of system: During each cycle the activated sludge system was aerated continuously and the produced CO2 trapped. During settling of the sludge after the 23 hours period, the whole CO2-trapping solution was removed and analyzed for CO2-content.
- Microbiological activity and solid content of water/sludge mixture: After each 23 hours (exceptionally 71 hours after week-ends) period of continuous aeration of the sludge unit, just before settling of the sludge, this mixture was sampled for determination of microbiological growth and concentration of solids in the sludge.

TEST CONCENTRATIONS
- Test concentrations: 0.10, 0.27, 0.72, 1.93, 5.18, 13.90, 37.28, 100 ppm imazalil in sewage solution

Reference substance (positive control):

no

Key result

Duration:

16 d

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Duration:

16 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Details on results:

Addition of imazalil up to 100.0 ppm did not seem to have reached the toxic limit as:
* COD reduction did not seem to be influenced,
* CO2-production remained stable,
* microbial growth, estimated by the Standard Plate Count Technique was not affected adversely,
* concentration of solids in the medium remained the same

Validity criteria fulfilled:

yes

Conclusions:

The influence of Imazalil on the operation of a sewage treatment plant was analysed. After repeated tests with increasing concentrations up to 100 ppm of Imazalil on a bench scale activated sludge unit, it was clearly indicated that Imazalil has no toxic or inhibitory effect on the biomass.

Description of key information

The study of Peeters et al. (1980), investigating the toxicity of Imazalil to STP microorganism, was considered as the key study for endpoint coverage. Addition of Imazalil up to 100 ppm did not reach the toxic limit which corresponds to 133 mg imazalil sulphate/L

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

133 mg/L