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Ecotoxicological information

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:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No standard test, but test well described and relevant ecological endpoint for evaluation the effect of thiosulfate on the N-cycle is evaluated (effect on urea hydrolysis).
Justification for type of information:
see attachment “Read-across concept – Human Health/Environment - Category approach for Inorganic sulfites/thiosulfates/dithionite" in section 13.
Principles of method if other than guideline:
ATS was added to urea-spiked soils, and urea levels were extracted and determined after 3 and 10 days using methods described by Douglas and Bremner (1970) and Mulvaney and Bremner (1979).
Details on preparation and application of test substrate:
The soils used were surface (0-15 cm) samples of Iowa soils selected to obtain a range in properties (Webster, Hayden, Harps, Storden). Each sample was air-dried and crushed to pass through a 2-mm screen
Test organisms (inoculum):
other: not specified
Total exposure duration:
10 d
Remarks:
samples were also analysed after 3 d
Test temperature:
20 degrees Celcius
Moisture:
2 mL in 5 gram of dried soil
Details on test conditions:
Five gram samples of air-dried soils were placed in 65-mL glass bottles and treated with 2 mL of water containing 10 mg of urea or with 2 mL of water containing 10 mg of urea and various amounts of the test compound. The bottles were stoppered and placed in an incubator at 20°C. After 3 and 10 days, triplicate bottles were removed from the incubator, and urea in the incubated soil samples was extracted and determined by a colorimetrc method.
Nominal and measured concentrations:
Nominal mg ATS/kg soil: 500, 1000, 2500, 5000
Duration:
3 d
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Webster, Harps, Storden soil
Duration:
3 d
Dose descriptor:
NOEC
Effect conc.:
>= 5 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Hayden soil
Duration:
3 d
Dose descriptor:
other: LOEC
Effect conc.:
2 500 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Webster, Harps, Storden soil
Duration:
10 d
Dose descriptor:
NOEC
Effect conc.:
2 500 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Webster soil
Duration:
10 d
Dose descriptor:
NOEC
Effect conc.:
>= 5 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Hayden, Harps, Storden soil
Duration:
10 d
Dose descriptor:
other: LOEC
Effect conc.:
5 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: retardation of urea hydrolysis
Remarks on result:
other: Webster soil
Details on results:
ATS significantlly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil).
Conclusions:
The effect of ammonium thiosulfate on urea hydrolysis was investigated in urea-spiked soils that were exposed to different concentration levels of ATS. ATS significantlly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil). These data can be used as supportive information for the assessment of thiosultfates in the terrestrial compartment.
Endpoint:
toxicity to soil microorganisms
Data waiving:
other justification
Justification for data waiving:
other:

Description of key information

Key value for chemical safety assessment

Additional information

In a supporting study by McCarty et al. (1990), the effect of ammonium thiosulfate on urea hydrolysis was investigated in urea-spiked soils that were exposed to different concentration levels of ammonium thiosulfate. Ammonium thiosulfate significantly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil), which are significantly above the OECD test limit of 1000 mg/kg soil. Thus, results indicate a low potential for the toxicity of thiosulfate substances on microbial nitrogen cycling in soil.