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Toxicity to microorganisms

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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2015-03-04 to 2015-06-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant study according to OECD guideline 209
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Method of cultivation: Stirred and aerated suspension cultures (180 min), fed with synthetic sewage (50 mL per L and d), test item added
- Preparation of inoculum for exposure: Activated sludge, municipal wastewater treatment plant Staufener Bucht (sampling date 2015-03-10), 1.5 g dry solids per litre
- Pretreatment: After sampling, the activated sludge was kept aerated. The activated sludge was washed twice by settling the sludge, decanting the supernatant and re-suspending the sludge in tap water. Before using, the activated sludge was diluted to 3 g/L dry solids with tap water, in order to obtain a final concentration of 1.5 g/L dry solids in the test.
- Initial biomass concentration: not reported. Dry weight of the activated sludge was determined as 5.9 g/L. A final concentration of 1.5 g d.w./L was used in the test.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Remarks on exposure duration:
Additional 3 min for measurement of respiration rate.
Test temperature:
18.8–19.9 °C
pH:
7.2-7.3 (blank vessels)
Dissolved oxygen:
After 180 min aeration: 4.30 mg/L to 5.82 mg/L
After measurement of respiration rate: 2.17 mg/L to 4.46 mg/L
Nominal and measured concentrations:
Nominal test item concentrations: 0 and 1000 mg/L (limit test)
Details on test conditions:
TEST SYSTEM
- Test vessel: 1000-mL beakers (Schott, Mainz, Germany)/250-300 mL BOD bottles
- Type (delete if not applicable): Open
- Fill volume: 500 mL for set-up
- Aeration: Stirred and aerated for 180 min at 0.5-1 L/min using room air (membrane pump)
- No. of organisms per vessel: Not applicable
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- Biomass loading rate: Not reported. Dry weight of the activated sludge was determined as 5.9 g/L. A final concentration of 1.5 g d.w./L was used in the test.

OTHER TEST CONDITIONS
- Adjustment of pH: No

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Respiration rate

TEST CONCENTRATIONS
- Spacing factor for test concentrations: not applicable (limit test)
- Range finding study: No
- Test concentrations: 0 and 1000 mg/L
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol 97 %
Duration:
3 h
Dose descriptor:
other: EL50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: NOEL
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
- Results with reference substance valid?: Yes
- Relevant effect levels: Whereas the addition of 1 mg/L of 3,5-D did not result in any inhibition of the respiration rate, the addition of 10 mg/L and 30 mg/L led to respiration inhibition of 57 % and 79 %, respectively. With the reference substance an EC50 of 8.9 mg/L was calculated.
Reported statistics and error estimates:
The EC50/EL50 calculation was performed with the ToxRat software by probit analysis using linear max. likelihood regression (ToxRat Standard Version 2.09, © ToxRat Solutions GmbH). The EC50/EL50 was calculated from the slope of the curve.

Table 1: Respiration rate of activated sludge after application of tantalum pentachloride

 Vessel O2 concentration in [mg/l], first measurement O2 concentration in [mg/l], last measurement Respiration rate [mg/(l*h)] Inhibition [%] 
 Blank 1 4.88  2.60  54.7  
 Blank 2  5.44  3.68  42.2  
 Blank 3*  5.17  4.46  17.0  
 Blank 4  5.21  3.37  44.2  
 Blank 5  5.51  3.61  45.6  
 Blank 6  4.30  2.17  51.1  
 Test 1000 mg/L 1  4.84  2.72  50.9  -7
 Test 1000 mg/L 2  5.82  3.64  52.3  -10
 Test 1000 mg/L 3  5.34  3.21  51.1  -7
            coefficient of variation of blanks: 0.10

*outlier, consumption rate too low

Validity criteria fulfilled:
yes
Conclusions:
An activated sludge respiration inhibition test according to OECD 209 resulted in an EL50 > 1000 mg/L and an NOEL ≥ 1000 mg/L. After 180 min no inhibitory effects were observed.
Executive summary:

To investigate potential harmful effects of tantalum pentachloride on aquatic microorganisms, an activated sludge respiration inhibition limit test was performed at nominal loadings of 0 mg/L (control) and 1000 mg/L according to OECD 209 and under GLP. No inhibiting effects were observed after 180 min. Hence an EL50 value of > 1000 mg/L and a NOEL of ≥ 1000 mg/L was determined.

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:
This information is used in a read-across approach in the assessment of the substance to be registered.

Reason / purpose:
read-across source
Duration:
3 h
Dose descriptor:
other: EL50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: NOEL
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
- Results with reference substance valid?: Yes
- Relevant effect levels: Whereas the addition of 1 mg/L of 3,5-D did not result in any inhibition of the respiration rate, the addition of 10 mg/L and 30 mg/L led to respiration inhibition of 57 % and 79 %, respectively. With the reference substance an EC50 of 8.9 mg/L was calculated.
Reported statistics and error estimates:
The EC50/EL50 calculation was performed with the ToxRat software by probit analysis using linear max. likelihood regression (ToxRat Standard Version 2.09, © ToxRat Solutions GmbH). The EC50/EL50 was calculated from the slope of the curve.

Table 1: Respiration rate of activated sludge after application of tantalum pentachloride

 Vessel O2 concentration in [mg/l], first measurement O2 concentration in [mg/l], last measurement Respiration rate [mg/(l*h)] Inhibition [%] 
 Blank 1 4.88  2.60  54.7  
 Blank 2  5.44  3.68  42.2  
 Blank 3*  5.17  4.46  17.0  
 Blank 4  5.21  3.37  44.2  
 Blank 5  5.51  3.61  45.6  
 Blank 6  4.30  2.17  51.1  
 Test 1000 mg/L 1  4.84  2.72  50.9  -7
 Test 1000 mg/L 2  5.82  3.64  52.3  -10
 Test 1000 mg/L 3  5.34  3.21  51.1  -7
            coefficient of variation of blanks: 0.10

*outlier, consumption rate too low

Validity criteria fulfilled:
yes
Conclusions:
An activated sludge respiration inhibition test according to OECD 209 resulted in an EL50 > 1000 mg/L and an NOEL ≥ 1000 mg/L. After 180 min no inhibitory effects were observed.
Executive summary:

To investigate potential harmful effects of tantalum pentachloride on aquatic microorganisms, an activated sludge respiration inhibition limit test was performed at nominal loadings of 0 mg/L (control) and 1000 mg/L according to OECD 209 and under GLP. No inhibiting effects were observed after 180 min. Hence an EL50 value of > 1000 mg/L and a NOEL of ≥ 1000 mg/L was determined.

This information is used in a read-across approach in the assessment of the substance to be registered.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

No toxic effect on microorganisms is expected since tantalum is insoluble in water. An activated sludge respiration inhibition test according to OECD 209 on tantalum pentachloride (source substance for read-acoss) resulted in an EL50 > 1000 mg/L and an NOEL ≥ 1000 mg/L. After 180 min no inhibitory effects were observed.

Key value for chemical safety assessment

Additional information

According to Annex VIII section 9.1.4 column 2 of the Regulation (EC) No 1907/2006 tests on the toxicity to microorganisms do not need to be conducted "if, there are mitigating factors indicating that aquatic toxicity is unlikely to occur, for instance if the substance is highly insoluble in water”. As the substance is expected to be highly insoluble (</= 21.3 µg/L), see section 4.8 (Fox, 2012), the substance is not expected to be toxic to aquatic microorganisms.

Nevertheless, toxicity data from read-across sources are used to describe the toxicity.To investigate potential harmful effects of tantalum pentachloride on microorganisms, an activated sludge respiration inhibition limit test was performed at concentrations of 0 mg/L (control) and 1000 mg/L according to OECD 209 and under GLP. No inhibiting effects were observed after 180 minutes. Therefore, an EL50 value of > 1000 mg/L and a NOEL of ≥ 1000 mg/L was determined.