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Toxicity to microorganisms

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Description of key information

Study was conducted according to OECD guideline 209, data are reliable without restrictions. 

Key value for chemical safety assessment

EC50 or LC50 for microorganisms:
320 mg/L

Additional information

In a study conducted according to OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test), three valid experiments were performed with Tellurium dioxide, fulfilling all validity criteria.

In the first experiment, a pre-test, the test item was tested using four concentrations (ranging from 1032 to 1 mg/L). Duration of the test was three hours. Activated sludge was used as inoculum. It was taken from a domestic sewage treatment plant and washed before usage.

The dry matter was determined as 3.18 g suspended solids/L, giving a concentration of 1.59 g suspended solids/L in the test.

As inhibition> 20 % was observed, and a full test was performed.

The second experiment, a full test, was performed using five concentrations, ranging from 322.0 to 3.2 mg/L. The dry matter of the activated sludge was determined as 2.8 g suspended solids/L, giving a concentration of 1.40 g suspended solids/L in the test.

Because significant inhibition in the lowest concentrated treatment occurred in the second experiment, a third experiment was performed in the same way using two lower concentrations of the test item, 1.0 and 0.32 mg/L, in order to determine a NOEC. The dry matter of the activated sludge was determined as 3.10 g suspended solids/L, giving a concentration of 1.55 g suspended solids/L in the test.

The following results for the test item Tellurium dioxide were determined:

3h NOEC =1.0 mg/L

3h EC10 = 3.7 mg/L (95% confid. interval: 2.7 - 5.1 mg/L)

3h EC50 =320 mg/L (95% confid. interval: 230 - 430 mg/L)

Justification for read-across:

This read-across is based on the hypothesis that source and target substances do possess similar ecotoxicological properties.

Since the physico-chemical behaviour of elemental Tellurium and Tellurium dioxide is the same with regard to their metabolic fate (reduction to the Telluride cation) there seems to be good evidence that Tellurium from different moieties will behave very similar with regard to systemic toxicity.

Elemental Tellurium and Tellurium dioxide are relatively poorly water soluble and their systemic uptake by environmental organisms will be directly comparable.

Thus the bioavailability will be an important factor for assessment of ecotoxicity of both substances. The water solubility of both substances is relatively low, with 1.7 and 2.5 mg/L for Tellurium and Tellurium dioxide, respectively.

Data from transformation dissolution tests at different pH values and loadings are available for both substances, indicating Tellurium dioxide to be more soluble at pH 8.

 

Corresponding standard information requirement

Source substance

Tellurium dioxide

Target substance

Tellurium

Water solubility

Transformation dissolution test: OECD guideline 29

 

Target pH 8 at 21.5 °C.

Loadings TeO2: Te concentrations after 7 days:

1 mg/L: 698.9 µg/L

10 mg/L: 6.254 mg/L

100 mg/L: 30.72 mg/L

Transformation dissolution test: OECD guideline 29

 

Target pH 8 at 21.5 °C.

Loadings: Te concentrations after 7 days:

1 mg/L: 20.02 µg/L

10 mg/L: 183.3 µg/L

100 mg/L:1.762 mg/L.

Water solubility:

OECD guideline 105

 

2.5 mg/L at 23 °C

pH 6.4

Water solubility:

OECD guideline 105

 

1.7 mg/L at 20 °C

pH 5.5 – 6.3

 

Underlying the basic assumption that effects caused by the bioavailable metal fraction and the same toxicokinetic behaviour (outlined in detail in the chapter toxicokinetic), ecotoxicity data from the relatively higher soluble Tellurium dioxide were considered appropriate for the ecotoxicity assessment of Tellurium.

In conclusion read-across is considered an appropriate adaptation for ecotoxicological endpoints to meet the standard information requirements according to REACH Regulation.

A detailed justification for read-across describing the toxicokinetic profile, comparing physico-chemical and toxicological properties as well as classification and labelling is outlined in IUCLID chapter 13 in a separate paper.