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Toxicity to microorganisms

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Reference
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:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Both the target substance Ferbam and the source substance Ziram quickly hydrolyse forming dimethyldithiocabamates. The analogue hypothesis is that both substances dissociate in acidic and neutral aqueous solutions to the common breakdown product dimethyldithiocarbamate, which determines the (eco-)toxicological properties. Therefore, the basis for this analogue approach is the “(Bio)transformation to common compound(s)” (scenario 1). This scenario covers the analogue approach for which the read-across hypothesis is based on (bio) transformation to common compound(s). For the REACH information requirement under consideration, the effects obtained in a study conducted with one source substance are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect(s) or absence of effect is predicted. The predicted strength of the effects may be similar or based on a worst-case approach (Read-Across Assessment Framework, RAAF, ECHA, 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
The source substance is Ziram (IUPAC name: zinc bis(dimethyldithiocarbamate , CAS no. 137-30-4; EC no. 205-288-3). Ziram is an organometallic mono-constituent substance with a typical purity of ca. 99% (w/w), ranging from > 98% to 100%. In general, impurities are known and are likely to vary depending on the manufacturing process, but are considered not relevant for classification or labelling of the substance.
The target substance is Ferbam (IUPAC name: N,N-dimethylcarbamodithioate;iron(3+), CAS no. 14484-64-1; EC no. 238-484-2). Also Ferbam is an organometallic mono-constituent substance, with a typical purity of ca. 99% (w/w), ranging from > 98% to 100%. In general, impurities are known and are likely to vary depending on the manufacturing process, but are considered not relevant for classification or labelling of the substance.
The substance identities and all REACH Annex VII and VIII information on physicochemical properties, environmental fate, ecotoxicity and toxicity are summarised in the read-across statement attached under section 13 of this IUCLID file. Both substances are dimethyldithiocarbamates with a central metal. The high structural similarity is also reflected in very similar physicochemical properties. Both substances are primarily used fungicides.

3. ANALOGUE APPROACH JUSTIFICATION
The toxicity of Ziram to microorganisms has been investigated in two activated sludge respiration inhibition tests according to OECD TG 209. In the key study (Hammesfahr, 2014) concentrations ranging from 10 to 1000 mg/L were tested. After 3h of exposure, the EC50 was determined as 58.8 mg/L. In a supportive study (Hanstveit, 1999), an EC50 of 19.2 mg/L was determined. Due to the similar hydrolysis, the read-across of the studies and their results is justified, as substances are applied in dilution to water.
For further information on the justification of the analogue approach please refer to the read-across statement attached under section 13 of this IUCLID file.

4. DATA MATRIX
Please refer to the data matrix in the read-across statement attached under section 13 of this IUCLID file.
Reason / purpose:
read-across source
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
58.8 mg/L
Validity criteria fulfilled:
yes
Conclusions:
The source substance Ziram technical was directly dosed into each test flask, which was subsequently filled with tap water. Ziram was dissolved into the tap water as homogeneously as possible.
Total respiration:
In comparison to the inoculum controls the respiration rates of the activated sludge were moderately inhibited by 27.4% and 33.0% at the test concentrations of 10 and 32 mg/L. For the concentrations of 100 mg/L and 320 mg/L the inhibition rates were 62.8% and 74.4%. The highest test concentration of 1000 mg/L resulted in an inhibition of 89.8%. Concentrations exceeding 1000 mg/L nominal were not tested.
Respiration without nitrification (Heterotrophic Respiration):
In comparison to the inoculum controls the respiration was not inhibited at a concentration of 10 mg/L. For the Ziram concentration of 32 mg/L and 100 mg/L the inhibition was 10.5% and 44.2%. At the concentrations of 320 mg/L and 1000 mg/L the respiration rates were strong inhibited by 60.4% and 79.9%.
The 3-hour EC50 for total respiration was calculated to be 58.8 mg/L. For heterotrophic respiration the 3-hour EC50 was 187.6 mg/L. For the oxygen uptake due to nitrification the 3-hour EC50 could not be calculated.
Executive summary:

The influence of the source substance Ziram technical on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of various concentrations of the test item after an incubation period of 3 hours.

The test was conducted according to DIN EN ISO 8192, EU Method C.11 and OECD Guideline # 209. Test concentrations were 10, 32, 100, 320 and 1000 mg Ziram technical/L; 3.2, 10 and 32 mg 3,5-Dichlorophenol/L and six inoculum controls.

Results:

The source substance Ziram technical was directly dosed into each test flask, which was subsequently filled with tap water. Ziram was dissolved into the tap water as homogeneously as possible.

Total respiration:

In comparison to the inoculum controls the respiration rates of the activated sludge were moderately inhibited by 27.4% and 33.0% at the test concentrations of 10 and 32 mg/L. For the concentrations of 100 mg/L and 320 mg/L the inhibition rates were 62.8% and 74.4%. The highest test concentration of 1000 mg/L resulted in an inhibition of 89.8%. Concentrations exceeding 1000 mg/L nominal were not tested.

Respiration without nitrification (Heterotrophic Respiration):

In comparison to the inoculum controls the respiration was not inhibited at a concentration of 10 mg/L. For the Ziram concentration of 32 mg/L and 100 mg/L the inhibition was 10.5% and 44.2%. At the concentrations of 320 mg/L and 1000 mg/L the respiration rates were strong inhibited by 60.4% and 79.9%.

The 3-hour EC50 for total respiration was calculated to be 58.8 mg/L. For heterotrophic respiration the 3-hour EC50 was 187.6 mg/L. For the oxygen uptake due to nitrification the 3-hour EC50 could not be calculated.

Description of key information

The Test was conducted according to DIN EN ISO 8192, EU Method C.11 and OECD Guideline # 209 and GLP.

The 3-hour EC50 for total respiration was calculated to be 58.8 mg/L. For heterotrophic respiration the 3-hour EC50 was 187.6 mg/L. For the oxygen uptake due to nitrification the 3-hour EC50 could not be calculated.

Key value for chemical safety assessment

EC50 for microorganisms:
58.8 mg/L

Additional information

The influence of the test item Ziram technical on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of various concentrations of the test item after an incubation period of 3 hours.

The Test was conducted according to DIN EN ISO 8192, EU Method C.11 and OECD Guideline # 209. Test concentrations were 10, 32, 100, 320 and 1000 mg Ziram technical/L; 3.2, 10 and 32 mg 3,5-Dichlorophenol/L and Six inoculum controls.

Results:

The test item Ziram technical was directly dosed into each test flask, which was subsequently filled with tap water. The test item was dissolved into the tap water as homogeneously as possible.

Total respiration:

In comparison to the inoculum controls the respiration rates of the activated sludge were moderately inhibited by 27.4% and 33.0% at the test concentrations of 10 and 32 mg/L. For the concentrations of 100 mg/L and 320 mg/L the inhibition rates were 62.8% and 74.4%. The highest test concentration of 1000 mg/L resulted in an inhibition of 89.8%. Concentrations exceeding 1000 mg/L nominal were not tested.

Respiration without nitrification (Heterotrophic Respiration):

In comparison to the inoculum controls the respiration was not inhibited at a concentration of 10 mg/L. For the test item concentration of 32 mg/L and 100 mg/L the inhibition was 10.5% and 44.2%. At the concentrations of 320 mg/L and 1000 mg/L the respiration rates were strong inhibited by 60.4% and 79.9%.

The 3-hour EC50 for total respiration was calculated to be 58.8 mg/L. For heterotrophic respiration the 3-hour EC50 was 187.6 mg/L. For the oxygen uptake due to nitrification the 3-hour EC50 could not be calculated.