Gallium arsenide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 24, 2010 to July 01, 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study conducted according to OECD 209 Guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Principles of method if other than guideline:

The respiration rates at the 2 highest treatment levels were set between 8.82 - 9.91 O2/L (outside the guideline range): in fact, the low respiration rates encountered at these treatment levels would otherwise impede calculation of respiration rates.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Details on sampling:

Chemical analysis of the test concentrations were not performed.

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Test solutions were prepared without using a stock solutions. The test item concentration levels: prepared by stirring corresponding amounts of the test item in 284 ml of deionised water; room temperature; in the dark for seven days (based on OECD 2001). Afterwards, the synthetic sewage feed and the microbial inoculum were added.
- Controls: The controls were prepared by combining 284 mL of temperature adapted dilution medium (deionised water) and 16 mL of the synthetic sewage feed and adding the microbial inoculum.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: the activated sludge was obtained from the sewage treatment works in Frankfurt/Main Niederrad, Germany, treating predominantly domestic sewage.
- Preparation of inoculum for exposure: Reconstituted water (OECD 1992) was used as washing medium for activated sludge. The activated sludge was washed three times. Between washings, the activated sludge was centrifuged for 2 minutes at 1000 rpm
- Pretreatment: before use, the inoculum was stored for 3 days at temperature of 20 ± 2 °C. During storage, 50mL synthetic sewage feed were added per liter activated sludge and per day. The activated sludge was stirred and aerated during storage
Synthetic sewage feed was prepared 1 week before use and consisted of peptone,meat extract, urea, NaCl, CaCl2*2H2O, MgSO4*7H20 and K2HPO4.
- Amount of microbial inoculum: 200 mL
- Amount of synthetic sewage feed: 16 mL

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Remarks on exposure duration:

Test period was a contact time

Test temperature:

20 ± 2°C
(20.4 to 20.9 °C - n=7)

pH:

pH-value of the activated sludge: 7.0

Nominal and measured concentrations:

Nominal concentrations (mg/L): 0; 9.5; 30.5; 98.0; 313.0; 1000.0.

Details on test conditions:

Tests were conducted according to OECD 209 Guidelines.
The only deviation refers to the respiration rates at the two highest treatment levels, which were assessed between 8.82 O2/L and 9.91 O2/L (outside the range recommended in the guideline). Reason for deviation is the low respiration rates encountered at these treatment levels: shifting the range allowed calculation of respiration rates.


TEST SYSTEM
- Storage time of the activated sludge before use: 3 days
- pH-value of the activated sludge: 7.0
- Amount of test mixture per test vessel: 500 mL
- Volume of microbial inoculum per test mixture: 200 mL
- Volume of synthetic sewage feed per test mixture: 16 mL
- Mixed liquor suspended solids level in the microbial inoculum: 4.35 g/L
- Mixed liquor suspended solids level in the final test mixtures: 1.74 g/L
- Test vessel: 1000 mL glass beakers without cover
- Type (delete if not applicable): open – without cover
- Aeration of test vessels: 40 to 50 L of air/hour (ambient air, oil-free air compressor)
- No. of vessels per concentration (replicates): 1 replicate was used per test item concentration
- No. of vessels per control (replicates): 2 replicates were used for control
- Contact period: 3 hours
- Temperature 20.4 to 20.9 °C


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : The respiration rate was calculated from the oxygen consumption of the test solutions as mg O2/L h.

TEST CONCENTRATIONS
- Test concentrations: the test item concentration levels were prepared by stirring corresponding amounts of the test item in 284 mL of deionised water at room temperature in the dark for 7 days (OECD 2001), before adding the synthetic sewage feed and microbial inoculum.
- Test concentrations: 5 concentration levels with nominal concentrations of 9.5, 30.5, 98.0, 313.0 and 1000.0 mg/L plus a control were tested.
- Control of the test system (reference test): 3,5-dichlorophenol was used as reference substance. The same batch of sludge was tested. The effect of the reference item was determined to ensure that the test conditions were reliable. Four concentration levels were tested.: 1.8, 5.9, 18.8, 60 mg/L were tested according to ET’s SOP A 16.1. EC50 (3h)= 11.2 is within the accepted range of 5-30 mg/L as required by the guidelines.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

4.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: Lower 95%-CL=0.1; Upper 95%-CL=- 18.0

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

317 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: Lower 95%-CL= 136.0; Upper 95%-CL= 739.0

Results with reference substance (positive control):

- Results with reference substance valid? Yes
3,5-dichlorophenol was used as reference item (tested on June 30, 2010).
The same batch of sludge was used like in the definitive test. In the reference test 4 concentration levels (1.8, 5.9, 18.8, 60 mg/L) were tested and the test was performed according to the ECT’s SOP A 16.1. EC50 (3h)= 11.2 mg/L is within the accepted range of 5-30 mg/L, as required by the guideline.

Reported statistics and error estimates:

Probit Analysis was used to determine the ECx- values. Calculations were run using the statistical software package ToxRat 2.10 Professional.

Validity criteria fulfilled:

yes

Conclusions:

Respiration inhibition (nominal values)-EC50 = 317.0 mg/L; EC10= 4.6 mg/L; EC20= 19.6 mg/L.
All validity criteria were fulfilled:
- the control respiration rates did not differ more than 15%, compare to each other: the reported value was 12.1%
- the EC50 (3h) of 3,5-dochlorophenol was in the accepted range of 5 to 30 mg/L: the reported value was 11.2 mg/L
Reported data are reliable and can be used for the efect assessment of GaAs on micro-organisms

Description of key information

Klimisch 1 study (Egeler P, Goth A (2010): activated sludge respiration inhibition test for GaAs according to OECD 209: EC50(3h) = 317.0 mg GaAs/L and EC10 = 4.6 mg GaAs/L (nominal values). Test was conducted with GaAs-powder; this physical form, however, is not relevant for the industrial production/use of GaAs where this substance is only present as a massive or as wafers. No toxicity data based on massive/wafer GaAs are available. Reported effects based on GaAs powder should therefore be considered as a worst case, predominantly reflecting the powder GaAs toxicity.

Key value for chemical safety assessment

EC50 for microorganisms:

317 mg/L

EC10 or NOEC for microorganisms:

4.6 mg/L

Additional information

A clear concentration-response relationship was observed and the following nominal ECx were determined for GaAs powder:

- EC₅₀= 317.0 mg GaAs/L

- EC₁₀= 4.6 mg GaAs/L

- EC₂₀= 19.6 mg GaAs/L