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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
See read-across justification report under Section 13 ‘Assessment Reports’.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In accordance with REACH Annex XI, Section 1.5, of Regulation (EC) No. 1907/2006 (REACH) the standard testing regime may be adapted in cases where a grouping or read-across approach has been applied.

The similarities may be based on:
(1) a common functional group
(2) the common precursors and/or the likelihood of common breakdown products via physical or biological processes, which result in structurally similar chemicals; or
(3) a constant pattern in the changing of the potency of the properties across the category


1. Both substances are inorganic salts of a monovalent cation from Group 2 of the periodic table, calcium or magnesium, and phosphoric acid. Thus, they all share the Ca2+ or Mg2+ cation and the PO43- anion as common functional groups.
2. Both substances will ultimately dissociate into the common breakdown products of the Ca2+ or Mg2+ cations and the PO43- anion.
3. Calcium and magnesium orthophosphates have been shown to have a similar toxicological profile and physicochemical nature and therefore this data is considered to be adequate and reliable for use in read-across. Any further testing would not be scientifically justified as all substances will dissociate to their anionic and cationic forms in natural waters and these ions (Ca2+, Mg2+ and PO43-) are all ubiquitous and are not considered to pose a risk of ecotoxicity.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See read-across justification report under Section 13 ‘Assessment Reports’.

3. ANALOGUE APPROACH JUSTIFICATION
See read-across justification report under Section 13 ‘Assessment Reports’.

4. DATA MATRIX
See read-across justification report under Section 13 ‘Assessment Reports’.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was directly added to the test medium and subsequently stirred for 24 hours.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Fresh samples of activated sludge were taken from a sewage treatment plant (Ruhrverband Kläranlage, Schmallenberg, Germany) mainly fed with municipal wastewater.
- Pretreatment: the sludge was washed with isotonic solution. A stock solution of activated sludge in tap water was prepared with a mixed liquor suspended solids level of 4.6 g dry mass sludge/liter. The sludge stock solution was fed with synthetic sewage feed and was
incubated aerated overnight at 20 ± 2 °C in the dark.
- Initial biomass concentration: 1.5 g/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2 °C.
pH:
8.1 - 8.2
Nominal and measured concentrations:
Nominal test substance concentrations: 10, 100, 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: Erlenmeyer flask, 1 L
- Material, fill volume: glass, 500 mL
- Aeration: yes
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 6 + 1 abiotic control


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionized water, free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions)


OTHER TEST CONDITIONS
- Adjustment of pH: yes, buffered to 7.5 ± 0.5 using H2SO4 (50 g/L) solution.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Microbial respiration rate (total oxygen uptake including heterotrophic and nitrification uptake)

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 1000 mg/L
- Results used to determine the conditions for the definitive study: EC50 > 1000 mg/L
Reference substance (positive control):
yes
Duration:
3 h
Dose descriptor:
other: EC20
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:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
No inhibition of the respiration rate was observed
Results with reference substance (positive control):
EC50: 2 - 25 mg/L.

Inhibition (%) of the respiration rate by the test item

Test item concentration

10 mg/L

100 mg/L

1000 mg/L

Inhibition

-14.1 %

-4.4 %

0.5 %

Validity criteria fulfilled:
yes
Conclusions:
There is no significant inhibition of bacterial respiration by Calcium bis(dihydrogenorthophosphate) up to and including a concentration of 1000 mg/L. The EC50 of the test item is > 1000 mg/L.

Description of key information

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

Experimental data on the toxicity of magnesium nis(dihydrogenorthophosphate) to aquatic microorganisms are not available. The assessment was therefore based on studies conducted with the analogue substance calcium bis(dihydrogenorthophosphate) (CAS 7758-23-8) as part of a read across approach, which is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5.

The effect of calcium bis(dihydrogenorthophosphate) on the respiration of activated sludge was tested in a study following OECD guideline 209. Activated sludge was exposed to nominal substance concentrations of 10, 100 and 1000 mg/L respectively. The oxygen consumption of the activated sludge was observed for 3 hours. An effect on the respiration rate of the activated sludge was not observed. At test termination an EC10> 1000 mg/L (nominal) was determined. Based on the read across data toxic effects of magnesium bis(dihydrogenorthophosphate) to aquatic microorganisms are not expected.