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Toxicity to soil microorganisms

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Endpoint:
toxicity to soil microorganisms
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
2008-09-11 to 2009-10-13
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
GLP study performed according to OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test) with the following deviation- the test substance characterization was not performed in accordance with GLP. The reliability of this study for the substance tested is a K1, but in application of read-across to a different substance ECHA’s guidance specifies that the score can be a maximum of K2. Due to lower transformation/dissolution results for tungsten carbide (the target substance) than sodium tungstate (the source substance), the resulting toxicity potential would also be expected to be lower, so read-across is appropriate. In addition, read-across is justified because the classification and labelling is the less severe for the target substance and the PBT/vPvB profile is the same. Finally, the dose descriptor for the target substance is expected to be sufficiently lower than the source chemical, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read across approach.
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH: The hypothesis is that properties are likely to be similar or follow a similar pattern because of the presence of a common metal ion, in this case tungstate.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES):
Source: Sodium Tungstate
Target: Tungsten Carbide
3. CATEGORY APPROACH JUSTIFICATION: See Annex 1 in CSR
4. DATA MATRIX: See Annex 1 in CSR
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test)
Deviations:
yes
Remarks:
The test substance characterization was not performed in accordance with GLP.
Principles of method if other than guideline:
not applicable
GLP compliance:
yes
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
not applicable
Analytical monitoring:
no
Details on sampling:
not applicable
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: Sandy clay loam, collected from Grand Forks North Dakota, April 7, 2009, at a depth of 4-8 inches from a field plot. Stored in a refrigerator at 4 deg. C until used. Immediately prior to use, soil was passed through a 2mm sieve.
- Other: not applicable


APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: 20 g aliquots (dry weight) of soil were weighed into eighteen 250 mL Pyrex bottles. Bottles were fitted with foam plugs for air exchange. Soil moisture was adjusted to 40-60% of water holding capacity. Soil samples were incubated 6 days at 20 deg C. Then, a 20.1 mg/mL stock solution was prepared using 503.9 mg sodium tungstate in a 25 mL volumetric flask, correcting for active ingredient content (99.9%) and bringing to volume with reagent water. Nine samples were dosed with 0.995 mL of the solution. The remaining nine were dosed with the same volume of reagent water only. Each sample was mixed thoroughly.


VEHICLE:
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): not applicable
- Concentration of vehicle in test medium (stock solution and final test solution): not applicable
- Evaporation of vehicle before use:not applicable
Test organisms (inoculum):
other: soil microorganisms
Total exposure duration:
28 d
Test temperature:
20 deg C
Moisture:
40-60% of the water holding capacity
Details on test conditions:
TEST SYSTEM
- Testing facility: ABC Labs, Columbia, Missouri
- Test container (type, material, size): 250 mL Pyrex
- Amount of soil: 20 g
- No. of replicates per concentration: 9
- No. of replicates per control: 9
- No. of replicates per vehicle control: N/A


SOIL INCUBATION
- Method: series of individual subsamples


SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): Grand Forks, North Dakota, N 47 deg 48.145', W097 deg 37.237'
- History of site:
- Vegetation cover: Field site
- Treatments with pesticides or fertilizers: Pesticide free
- Depth of sampling: 4-8 inches
- Soil texture
- % sand: 59%
- % silt: 18%
- % clay: 23%
- Soil taxonomic classification: Sandy clay loam
- Soil classification system: USDA texture
- pH (in water): 7.1
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): N/A
- Maximum water holding capacity (in % dry weigth): N/A
- Cation exchange capacity (mmol/kg): 17.0
- Pretreatment of soil: Passed through 2 mm sieve
- Storage (condition, duration): refrigerated
- Initial microbial biomass as % of total organic C: 1.25%


DETAILS OF PREINCUBATION OF SOIL (if any): 6 days at 20 deg C


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Respiration rate- Day 0 and Day 28


VEHICLE CONTROL PERFORMED: no


RANGE-FINDING STUDY
- Test concentrations: 0, 10, 100, 500 and 1,000 ug/g
- Results used to determine the conditions for the definitive study: yes
Nominal and measured concentrations:
Nominal- Control (0 mg/kg) and 1000 mg sodium tungstate/kg soil d.w.
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
other: sodium tungstate concentration
Basis for effect:
respiration rate
Details on results:
- Effect concentrations exceeding solubility of substance in test medium: none
- Other: not applicable
Results with reference substance (positive control):
not applicable
Reported statistics and error estimates:
The EC50 could not be calculated due to a lack of carbon transformation inhibition by the test substance.

Results

-Microbial plate counts at Day 0 and Day 28 in the treatment (6.0 x E6: Day 0, 1.2 x E7: Day 28) and control 1.6 x E6: Day 0 and 1.1 x E7: Day 28) indicated that the microbial populations remained active and viable during the course of the study.

-The average respiration rate of the Day 0 test substance was 89.3 mg/kg/hr, which differed from the average control respiration rate of 90.6 mg/kg/hr by -1.2%.

-The average respiration rate of the Day 28 test substance was 89.3 mg/kg/hr, which differed from the average control respiration rate of 92.3 mg/kg/hr by -3%.

-These results indicate that the test substance was not inhibitory to the carbon transformation process.

Validity criteria fulfilled:
yes
Conclusions:
The test substance does not inhibit the carbon tranformation process at concentrations of up to 1000 mg test substance/kg soil d.wt.
Executive summary:

No toxicity to soil microorganisms data of sufficient quality are available for tungsten carbide (target substance). However, toxicity to soil microorganisms data are available for sodium tungstate (source substance), which will be used for reading across. Due to lower water solubility and lower toxicity for the target substance compared to the source substance, the resulting read across from the source substance to the target substance is appropriate as a conservative estimate of potential toxicity for this endpoint. In addition, read across is appropriate because the classification and labelling is more protective for the source substance than the target substance, the PBT/vPvB profile is the same, and the dose descriptors are, or are expected to be, lower for the source substance. For more details, refer to the read-across category approach included in the Category section of this IUCLID submission and/or as an Annex in the CSR.

Endpoint:
toxicity to soil microorganisms
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
2008-09-11 to 2009-10-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
GLP study performed according to OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test) with the following deviations- the test substance and reference substance characterizations were not performed in accordance with GLP. The reliability of this study for the substance tested is a K1, but in application of read-across to a different substance ECHA’s guidance specifies that the score can be a maximum of K2. Due to similar or lower transformation/dissolution results for tungsten carbide (the target substance) than sodium tungstate (the source substance), the resulting toxicity potential would also be expected to be similar or lower, so read-across is appropriate. In addition, read-across is justified because the classification and labelling is the same or less severe for the target substance PBT/vPvB profile is the same. Finally, the dose descriptors are, or are expected to be, sufficiently similar or higher for the target substance, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read across approach.
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH: The hypothesis is that properties are likely to be similar or follow a similar pattern because of the presence of a common metal ion, in this case tungstate.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES):
Source: Sodium Tungstate
Target: Tungsten Carbide
3. CATEGORY APPROACH JUSTIFICATION: See Annex 1 in CSR
4. DATA MATRIX: See Annex 1 in CSR
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
yes
Remarks:
The test substance and reference substance characterizations were not performed in accordance with GLP.
Principles of method if other than guideline:
N/A
GLP compliance:
yes
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
N/A
Analytical monitoring:
no
Details on sampling:
N/A
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: Sandy clay loam, collected from Grand Forks North Dakota, April 7, 2009, at a depth of 4-8 inches from a field plot. Stored in a refrigerator at 4 deg. C until used. Immediately prior to use, soil was passed through a 2mm sieve.
- Other: not applicable


APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: 20 g aliquots (dry weight) of soil were weighed into eighteen 250 mL Pyrex bottles. Bottles were fitted with foam plugs for air exchange. Soil moisture was adjusted to 40-60% of water holding capacity. Soil samples were incubated 6 days at 20 deg C. Then, a 20.1 mg/mL stock solution was prepared using 503.9 mg sodium tungstate in a 25 mL volumetric flask, correcting for active ingredient content (99.9%) and bringing to volume with reagent water. Nine samples were dosed with 0.995 mL of the solution. The remaining nine were dosed with the same volume of reagent water only. Each sample was mixed thoroughly.


VEHICLE:
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): not applicable
- Concentration of vehicle in test medium (stock solution and final test solution): not applicable
- Evaporation of vehicle before use:not applicable
Test organisms (inoculum):
other: soil microorganisms
Total exposure duration:
28 d
Test temperature:
20 deg C
Moisture:
40-60% of the water holding capacity
Details on test conditions:
TEST SYSTEM
- Testing facility: ABC Labs, Columbia, Missouri
- Test container (type, material, size): 250 mL Pyrex
- Amount of soil: 20 g
- No. of replicates per concentration: 9
- No. of replicates per control: 9
- No. of replicates per vehicle control: N/A


SOIL INCUBATION
- Method: series of individual subsamples


SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude):Grand Forks, North Dakota, N 47 deg 48.145', W097 deg 37.237'
- History of site:
- Vegetation cover: Field site
- Treatments with pesticides or fertilizers: Pesticide free
- Depth of sampling: 4-8 inches
- Soil texture
- % sand: 59%
- % silt: 18%
- % clay: 23%
- Soil taxonomic classification: Sandy clay loam
- Soil classification system: USDA texture
- pH (in water): 7.1
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): N/A
- Maximum water holding capacity (in % dry weigth): N/A
- Cation exchange capacity (mmol/kg): 17.0
- Pretreatment of soil: Passed through 2 mm sieve
- Storage (condition, duration): refrigerated
- Initial microbial biomass as % of total organic C: 1.25%


DETAILS OF PREINCUBATION OF SOIL (if any): 6 days at 20 deg C


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Respiration rate- Day 0 and Day 28


VEHICLE CONTROL PERFORMED: no


RANGE-FINDING STUDY
- Test concentrations: Control, 1, 10, 100, 500 and 1000 ug of sodium tungstate/g of soil.
- Results used to determine the conditions for the definitive study: yes
Nominal and measured concentrations:
Nominal- Control (0 mg/kg) and 1000 mg sodium tungstate/kg soil
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Remarks on result:
other: highest concentration tested
Details on results:
The percent inhibition on day 28, based on nitrate concentration, was -8.8% in the 1,000 mg/kg treatments.
Results with reference substance (positive control):
N/A
Reported statistics and error estimates:
The 28 day EC50 was > 1000 mg/kg, the highest concentration tested.

Results

-Microbial plate counts at Day 0 and Day 28 in the treatment (8.7 x 106, Day 0, 7.1 x 107Day 28) and control 7.9 x 106Day 0 and 6.4 x 107Day 28) indicated that the microbial populations remained active and viable during the course of the study.

-The percent inhibition on Day 28 based on nitrogen concentration, was -8.8% in the 1000 mg test substance/kg .

-These results indicate that the test substance was not inhibitory to the carbon transformation process.

Conclusions:
The 28 day EC50 for the effect of sodium tungstate on nitrogen transformation based on nitrogen concentrations in the soil extracts was estimated to be > 1000 mg sodium tungstate/kg, the highest concentration tested.
Executive summary:

No toxicity to soil microorganisms data of sufficient quality are available for tungsten carbide (target substance). However, toxicity to soil microorganisms data are available for sodium tungstate (source substance), which will be used for reading across. Due to lower water solubility and lower toxicity for the target substance compared to the source substance, the resulting read across from the source substance to the target substance is appropriate as a conservative estimate of potential toxicity for this endpoint. In addition, read across is appropriate because the classification and labelling is more protective for the source substance than the target substance, the PBT/vPvB profile is the same, and the dose descriptors are, or are expected to be, lower for the source substance. For more details, refer to the read-across category approach included in the Category section of this IUCLID submission and/or as an Annex in the CSR.

Description of key information

Tungsten carbide was not tested for toxicity to soil micro-organisms and read-across to sodium tungstate was used for this endpoint. In both a Carbon and a Nitrogen Transformation Test using sodium tungstate the 28-day EC50 was found to be > 1000 mg/kg soil d.w. (sodium tungstate concentration) (nominal)  (approximately  586 mg W/kg). Read-across to sodium tungstate is appropriate as sodium tungstate is of higher solubility under simulated environmental conditions and has the same classification and PBT profile as tungsten carbide.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:
586 mg/kg soil dw

Additional information

Due to similar or lower transformation/dissolution results for tungsten carbide (the target substance) than sodium tungstate (the source substance), the resulting toxicity potential would also be expected to be similar or lower, so read-across is appropriate. In addition, read-across is justified because the classification and labeling is the same or less severe for the target substance, and the PBT/vPvB profile is the same. Finally, the dose descriptors are, or are expected to be, sufficiently similar or higher for the target substance, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read across approach.