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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:

See attached document in section 13 "Assessment report" for justification and rationale of the analogy approach.
Original letters from the French Competent Authorities requiring the read across to be done with cerium and iron oxide isostearate are attached below.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Conclusions:

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effect on the respiration rate of activated sludge micro-organisms up to and including the highest concentration tested of 1000 mg/L.

Executive summary:

The source and target substances present similar characterization (nanoparticles of very similar parameters), and similar physico-chemical and ecotoxicological properties (high melting point, low vapour pressure, very low water solubility, no expected bioaccumulation potential when considering cerium and iron elements and isostearate parts, no acute toxicity to daphnids up to and including the saturation concentration). This similarity supports the relevance of the read-across.

Thus, the toxicity to aquatic micro-organisms is expected to be the same for the source and target substances.

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effect on the respiration rate of activated sludge micro-organisms up to and including the highest concentration tested of 1000 mg/L.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 8 October 2001 to 17 January 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

temperature was slightly higher than 22°C during culture period (24°C) and test period (23°C).

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
All test item concentrations (10, 31.6, 100, 316 and 1000 mg/L) were higher than the water solubility of the test item (determined as 11.9 µg/mL at 20.9°C).
- Method: Test solutions at 100, 316 and 1000 mg/L were therefore prepared by direct addition of the test item in the test vessels and vigorous agitation of these solutions for a few minutes before the beginning of the test. The pH at 1000 mg/L was 7.99. Test solutions at 10 and 31.6 mg/L were prepared by means of a stock solution at 60 mg/L in dechlorinated water agitated during 10 minutes, and dilution of this suspension maintained under agitation.
- Controls: negative control (inoculum only) and positive control (inoculum + 3,5-dichlorophenol)
- Evidence of undissolved material: test solution was a suspension

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: no, activated sludge came from the water treatment plant of Evreux (France) containing effluent from a predominantly domestic origin.
- Method of cultivation: under agitation and synthetic sewage feed (50 mL/L) for one day before use. The temperature varied between 23 and 24 °C, and the stock vessel was kept away from light by wrapping it in opaque material. Aeration was provided by passing clean air through the inoculum at a rate of 0.5 to 1 L/min until use.
- Preparation of inoculum for exposure: The inoculum was left to settle and the supernatant rejected. It was then filtered and washed with dechlorinated water. Four samples of 50 mL were taken to determine the content in suspended matter (dry weight).
- Initial biomass concentration: The concentration of sludge (3.78 g/L) was not adjusted because the quantity of suspended mater was 4 g/L.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

none

Hardness:

280 ± 20 mg/L as CaCO3

Test temperature:

23°C

pH:

7.99 at 1000 mg/L

Nominal and measured concentrations:

Nominal concentrations: 10, 31.6, 100, 316 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: flask
- fill volume: 500 mL
- Aeration: yes (0.5 to 1 L of air/minute until the start of oxygen concentration measurements)
- No. of organisms per vessel: 1.6 g inoculum/L
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2 (inoculum only), 1 (inoculum + reference substance)
- Biomass loading rate: 1.6 g inoculum/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated tap water
- Culture medium different from test medium: no
- Intervals of water quality measurement: no data

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: no special precaution were taken
- Light intensity: no data

EFFECT PARAMETERS MEASURED: oxygen concentration was measured after 3 hours of contact for a period of approximately 10 minutes. Measurement of oxygen concentration was determined using an oxygen probe placed into an opaque BOD (Biological Oxygen Demand) flask filled with the test item or the reference solutions which was agitated with a magnetic stirrer. The oxygen probe was connected to a meter and to a chart recorder. The respiration rate was determined from the recorder trace in term of mg O2/L/h.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- Range-finding study: none

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol tested at 4, 12 and 36 mg/L

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

The respiration rate of the test solution of highest concentration (1000 mg/L) was equivalent to the respiration rate of the first control. Therefore, the oxygen consumption rate of the four other test solutions (10 to 316 mg/L) was not determined.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: 3h EC50 = 8.64 mg/L (95% CL: 7.01 - 10.4 mg/L). This value is within the guideline-recommended range of 5 to 30 mg/L; confirming suitability of the activated sludge used.

Reported statistics and error estimates:

The 3h-EC50 of the test item could not be calculated due to the absence of toxic effect. Probit analysis was used to calculate the EC50 of the reference substance and Fieller's method to calculate confidence interval limits.

Table 1: respiration rate in mg O2/L/h

	Concentration (mg/L)	Respiratory rate (mg O2/L/h)	Inhibition (%)
Control 1 Control 2	0 0	60.0 55.0	0 0
Reference item	4 12 36	45.0 18.1 8.6	22 69 85
Test item	10 31.6 100 316 1000	ND ND ND ND 55	4

ND = not determined

Validity criteria fulfilled:

yes

Conclusions:

Cerium and iron oxide isostearate has no toxic effect on the respiration rate of activated sludge micro-organisms up to and including the highest concentration tested of 1000 mg/L.

Executive summary:

The effect of cerium and iron oxide isostearate on the respiration of activated sewage sludge was evaluated using a 3-hour static test according to OECD guideline No. 209 and GLP. Five concentrations of test item were tested: 10, 31.6, 100, 316 and 1000 mg/L. In parallel, two controls and three different concentrations of the reference item 3,5-dichlorophenol (4, 12 and 36 mg/L) were tested. After a 3-hour incubation time, the inhibition of the respiration rate was investigated via measurement of oxygen consumption rate. 

The results of the reference treatments (EC50 = 8.64 mg/L within the guideline-recommended range of 5 - 30 mg/L) confirmed suitability of the activated sludge and the method used.

The respiration rate of the test solution of highest concentration (1000 mg/L) was equivalent to the respiration rate of the first control. Therefore, the oxygen consumption rate of the four other test solutions (10 to 316 mg/L) was not determined. And, a 3-hour EC50 > 1000 mg/L is determined.

 

Cerium and iron oxide isostearate should be considered as non-toxic for micro-organisms of a water treatment plant.

Description of key information

By analogy with cerium and iron oxide isostearate (active matter of DPX10), iron oxide isostearate (active matter of DPX13) is not considered to have any toxic effect on the respiration rate of activated sludge microorganisms.

Additional information

One GLP-compliant study performed according to OECD guideline 209 is available on the analogue, cerium and iron oxide isostearate (active matter of DPX10). It is quoted as reliability 1 according to Klimisch criteria and flagged as a key study.