Sodium O-isobutyl dithiocarbonate

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

other: published data

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Carbon disulphide is both a reagent in the manufacture, as well as a decomposition product of xanthates. SIBX readily decomposes to carbon disulphide, especially in the presence of moisture/water. Therefore, the health effects of carbon disulphide (CS2) need to be considered in the assessment of SIBX.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The test compound was added to 10 g of soil in a closed flask. Ammonium-N (200 mg/kg) was also added to the soil. Incubation was carried out at 25 ºC. After 5 and 14 days incubation the soil was analysed for ammonium-N, and for nitrite + nitrate-N. The inhibition of nitrification was calculated from the data.

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

no

Test organisms (inoculum):

soil

Total exposure duration:

14 d

Remarks:

Also sampling after 5 days.

Test temperature:

25 °C

Moisture:

60% of maximum water-holding capacity.

Nominal and measured concentrations:

0.1, 0.5, 1, 2 and 10 mg/kg soil (nominal)

Reference substance (positive control):

yes

Remarks:

Nitrapyrin (2-chloro-6-(trichlomethyl)pyridine)

Duration:

5 d

Dose descriptor:

EC50

Effect conc.:

0.21 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

nitrate formation rate

Remarks on result:

other: Harps clay loam

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

2.1 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

nitrate formation rate

Remarks on result:

other: Harps clay loam

Duration:

5 d

Dose descriptor:

EC50

Effect conc.:

0.475 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Sodium isobutyl xanthate

Basis for effect:

nitrate formation rate

Remarks on result:

other: On a molecular weight scaled basis, the EC50 would be 0.475 mg/kg soil dw. (0.21 x 172.24) /76.13 =0.475 mg/kg soil dw

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

4.75 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Sodium isobutyl xanthate

Basis for effect:

nitrate formation rate

Remarks on result:

other: On a molecular weight scaled basis, the EC50 would be 4.75 mg/kg soil dw. (2.1 x 172.24) /76.13 =4.75 mg/kg soil dw

Details on results:

The inhibition of nitrification by CS2 (5 mg/kg) after 7 days was 98% in Harps clay loam, 98% in Webster clay loam and 99% in Storden sandy clay loam.
Percentage inhibition of nitrification at different concentrations CS2 after 5 and 14 days in Harps soil is given in the table below.

Results with reference substance (positive control):

The inhibition of nitrification in Harps soil by nitrapyrin (10 mg/kg) was 64% after 5 days and 73% after 14 days.

Reported statistics and error estimates:

The summarizer calculated the EC50 vaues by Probit Analysis.

Validity criteria fulfilled:

not specified

Conclusions:

On a molecular weight scaled basis, the EC50 would be 4.75 mg/kg soil dw. (2.1 x 172.24) /76.13 =4.75 mg/kg soil dw
The nitrification in three soil types was inhibited by CS2. The 5-d EC50 in Harps clay loam soil was 0.21 mg/kg soil dw and the 14-d EC50 was 2.1 mg/kg soil dw.

Executive summary:

The effect of CS2 on nitrification in three soil types was investigated. Soil samples were placed in bottles and treated with ammonium sulphate (200 mg N/kg). Water was added to bring the soil moisture to 60% of maximum water-holding capacity. The bottles were sealed with screw caps fitted with a valve for injection of CS2. The test compound was added to the soil via the injection port and then the soil incubated at 25 ºC . After 5 and 14 days soil samples were analysed for ammonium-N, and for nitrite + nitrate-N. The 5-d EC50 in Harps clay loam soil was 0.21 mg/kg and the 14-d EC50 was 2.1 mg/kg soil dw. NOEC values were not given. The inhibition of nitrification by 5 mg CS2/kg after 7 days was 98% in Harps clay loam, 98% in Webster clay loam and 99% in Storden sandy clay loam.

Reference 3

Endpoint:

toxicity to soil microorganisms

Type of information:

other: published data

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Carbon disulphide is both a reagent in the manufacture, as well as a decomposition product of xanthates. SIBX readily decomposes to carbon disulphide, especially in the presence of moisture/water. Therefore, the health effects of carbon disulphide (CS2) need to be considered in the assessment of SIBX.

Qualifier:

no guideline available

Principles of method if other than guideline:

Soil samples from the field were incubated with CS2 (10 mg/kg) in sealed flasks. Incubation was carried out for 24 h at 25 °C. Thereafter the CS2 was removed and further incubation carried out for 10 days.
Other soil samples were fumigated with CS2 (i.e. exposed to CS2 vapour for 24 h in a desiccator). After removal of CS2 the soil was inoculated with fresh soil and further stored for 10 days.
The following parameters were determined: oxygen consumption, CO2 evolution and N-mineralisation (no details given on analytical methods).

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

no

Test organisms (inoculum):

soil

Total exposure duration:

1 d

Remarks:

One day exposure, 10 days further incubation.

Test temperature:

25 °C

Moisture:

55% of maximum water-holding capacity

Details on test conditions:

Soils were taken from Rothamsted Experimental Station, UK
Soil samples from the field were incubated with CS2 (10 mg/kg) in sealed flasks of 100 mL. Incubation was carried out for 24 h at 25 °C. Thereafter the CS2 was removed and further incubation carried out for 10 days.
Other soil samples were fumigated with CS2 (i.e. exposed to CS2 vapour for 24 h in a desiccator). After removal of CS2 the soil was inoculated with fresh soil and further stored for 10 days at 20 °C.

Nominal and measured concentrations:

10 mg/kg or fumigation

Reference substance (positive control):

not specified

Duration:

1 d

Dose descriptor:

EC50

Effect conc.:

10 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Duration:

1 d

Dose descriptor:

EC50

Effect conc.:

22.6 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Sodium isobutyl xanthate

Basis for effect:

nitrate formation rate

Remarks on result:

other: On a molecular weight scaled basis, the EC50 would be 22.6 mg/kg soil dw. (10x 172.24) /76.13 =22.6 mg/kg soil dw

Details on results:

On a molecular weight scaled basis, the EC50 would be 22.6 mg/kg soil dw. (10x 172.24) /76.13 =22.6 mg/kg soil dw
Used in high concentratiosn as a soil fumigant CS2 affected metabolism in soil; the amount of mineralised N increased 10-fold in 10 days. The oxygen consumption tripled and the evolution of CO2 more than doubled. Used at low concentrations (10 mg/kg) the nitrification was completely inhibited, with lesser effects on soil respiration.

Reported statistics and error estimates:

The summarizer calculated the EC50 vaues by Probit Analysis.

Validity criteria fulfilled:

not specified

Conclusions:

On a molecular weight scaled basis, the EC50 would be 22.6 mg/kg soil dw. (10x 172.24) /76.13 =22.6 mg/kg soil dw
After fumigation of soils with CS2 the microbial metabolism of soil was seriously affected. At 10 mg CS2/kg the nitrification was completely inhibited.

Executive summary:

Soil samples from the field were incubated with CS2 (10 mg/kg) in sealed flasks. Incubation was carried out for 24 h. Thereafter the CS2 was removed and further incubation carried out for 10 days.

Other soil samples were fumigated with CS2. After removal of CS2 the soil was inoculated with fresh soil and further stored for 10 days. The following parameters were determined: oxygen consumption, CO2 evolution and N-mineralisation.

Used in high concentrations as a soil fumigant CS2 affected metabolism in soil; the amount of mineralised N increased 10-fold in 10 days. The oxygen consumption tripeled and the evolution of CO2 more than doubled. Used at low concentrations (10 mg/kg) the nitrification was completely inhibited by CS2, with lesser effects on soil respiration.

NB: The increase of oxygen consumption, evolution of CO2 and N-mineralisation after fumigation can be explained by killing of microbial biomass and subsequent mineralisation of the killed biomass by the inoculum.

Description of key information

On a molecular weight scaled basis, the 1d EC50 would be 22.6 mg/kg soil dw. (10x 172.24) /76.13 =22.6 mg/kg soil dw
After fumigation of soils with CS2 the microbial metabolism of soil was seriously affected. At 10 mg CS2/kg the nitrification was completely inhibited.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:

22.6 mg/kg soil dw

Long-term EC10 or NOEC for soil microorganisms:

0.95 mg/kg soil dw

Additional information

On a molecular weight scaled basis, the EC50 would be 22.6 mg/kg soil dw. (10x 172.24) /76.13 =22.6 mg/kg soil dw After fumigation of soils with CS2 the microbial metabolism of soil was seriously affected. At 10 mg CS2/kg the nitrification was completely inhibited.

The nitrification in three soil types was inhibited by CS2. The 5-d EC50 in Harps clay loam soil was 0.21 mg/kg soil dw and the 14-d EC50 was 2.1 mg/kg soil dw.

On a molecular weight scaled basis, the EC50 would be 4.75 mg/kg soil dw. (2.1 x 172.24) /76.13 =4.75 mg/kg soil dw(NOEC=0.95 mg/kg soil)