Sodium dimethyldithiocarbamate

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

11 Jul - 21 Dec 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)

Version / remarks:

21 Jan 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Hessisches Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany (13 Mar 2017)

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

AMENDMENT OF SOIL
- Type of organic substrate: The soil (loamy sand) was amended with finely powdered lucerne green grass meal. The analysed carbon and nitrogen content was 40.9% and 2.7%, respectively. The ratio of carbon to nitrogen was 15.0 / 1.0.
- Other: No pesticides or organic or mineral fertilizer had been used on the soil for at least four years prior to test initiation.
- Other: The soil water content was determined in one replicate of each treatment group of both tests at each sampling.

APPLICATION OF TEST SUBSTANCE TO SOIL
- Application method of the test item: The aqueous test item solution was soluble in water. Therefore, a stock solution in pure water was prepared and mixed into the soil by means of a laboratory mixer. To this end, a stock solution was prepared by dissolving 5000 mg test item (aqueous solution) in 50 mL pure water. An aliquot of the stock solution and additionally 0.5% lucerne meal (related to soil dry weight) were mixed to the soil using a laboratory mixer. Throughout the application, the soil was ventilated and the soil water content was adjusted to 45% and 46% Water Holding Capacity (WHC).
- Application of the control: For the control, only pure water was mixed into the soil. To this end, pure water with 0.5% lucerne meal (based on soil dw) was prepared and added to the soil. The soil water content was adjusted to 45% WHC.

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

20 ± 2 °C

Moisture:

44 - 46% of maximum holding capacity (WHCmax)

Details on test conditions:

TEST SYSTEM
- Testing facility: Laboratory
- Test container: Approximately 0.5 L disposable plastic boxes filled up to 6 cm (dimension: 0.10 m width x 0.10 m depth x 0.065 height)
- Amount of soil: 200 g soil dw
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOIL INCUBATION
- Method: Series of individual subsamples. The soil was filled loosely into disposable plastic boxes, which were covered by perforated lids to allow air exchange to ensure aerobic incubation conditions.

SOURCE AND PROPERTIES OF SUBSTRATE
- Geographical reference of sampling site: "In der Speyerer Hohl", No. 977, 67354 Mechtersheim, Rhineland Palatinate, Germany. Sampled on 16 Oct 2017
- History of site: No pesticides or organic or mineral fertilizer had been used on the soil for at least four years prior to test initiation.
- Vegetation cover: Fallow grassland
- Treatments with pesticides or fertilizers: No
- Depth of sampling: 0.05 - 0.2 m
- Soil texture: Loamy sand
- % sand: 54.3
- % silt: 34.5
- % clay: 11.2
- Soil taxonomic classification: Standard soil F5M (LUFA, Speyer, Germany)
- pH (in water): 7.3
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): 13.938
- Maximum water holding capacity (in % dry weigth): 41.6
- Cation exchange capacity: 15.7 meq/100 g dw
- Pretreatment of soil: After sampling (16 Oct 2017), the soil was brought to the laboratory and air-dried and sieved (2 mm mesh) at room temperature (17 Oct 2017).
- Storage: The soil was stored at 20 °C ± 2 °C with appropriate ventilation and periodical moisture adjustment. The soil was pre-incubated from 26 Oct to 23 Nov 2017 (28 d).
- Initial microbial biomass as % of total organic C: 2.51

DETAILS OF PREINCUBATION OF SOIL:
The soil was stored at 20 ± 2 °C with appropriate ventilation and periodical moisture adjustment from 26 Oct to 23 Nov 2017 (28 d). The soil dry weight prior test start was 88.4%.

EFFECT PARAMETERS MEASURED:
Nitrogen transformation was determined in soil enriched with lucerne meal by comparison of test item treated soil with a non-treated soil. Nitrate nitrogen (NO3- nitrogen) formed in the nitrification process was determined. Soil samples were taken within 6 h after application and on Day 28 and Nitrite-N (NO2- nitrogen) and Nitrate-N + Nitrite-N (NO3- and NO2- nitrogen) contents were measured by continuous flow analysis. The Nitrate-N (NO3- nitrogen) concentration was then calculated from the measured values by substracting the NO2- nitrogen concentrations from the NO3- + NO2- nitrogen concentrations.

Nominal and measured concentrations:

80, 160, 320, 640, and 1000 mg test item (aq. sol)/kg soil dw (nominal)
32.88, 65.76,131.52, 263.04, and 411 mg a.i./kg soil dw (nominal)

Reference substance (positive control):

yes

Remarks:

sodium chloride

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

640 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

263.04 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

nitrate formation rate

Details on results:

- Effect concentrations exceeding solubility of substance in test medium: No

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: After 28 d exposure to 16 g reference item (sodium chloride), the soil nitrate content was -61.00% compared to the control and the soil nitrate formation rate was -101.80% compared to the control.
- Other: The reference item had a retarding effect of more than ± 25% compared to the control on day 28 and 97 after application. The results of the study confirmed the sensitivity of the test system and the adequacy of the laboratory testing conditions.

Reported statistics and error estimates:

Statistical analyses were performed with ToxRat Professional, version 3.2.1 (ToxRat Solutions GmbH). Normality and homogeneity of variances were tested with the Shapiro-Wilk's Test (alpha = 0.01) and Levene's test (alpha = 0.01), respectively and one-sided comparisons of treated and control values according to Williams t-test (alpha = 0.05) were conducted.
Since only the highest treatment clearly showed an inhibitin effect on day 28, a NOEC was derived. Data for soil nitrogen-N content on day 0 and 28 and the cumulative nitrate formation rate were tested for normality and homogeneity of variance with the Shapiro-Wilk's test and Levene's test, respectively. The trend analysis by contrasts revealed a linear trend. Therefore, the Williams multiple sequential t-test procedure was performed (one-sided smaller, alpha = 0.05).

VALIDITY CRITERIA

The study fulfilled the validity criteria laid down by the guideline (Table 1).

Table 1. Validity criteria OECD 216.

Criterion	Outcome	Criterion fulfilled
The variation between replicate control samples was less than ± 15%.	The coefficients of variation were 2.01 on day 0 and 2.93 on day 28.	Yes
The reference item had a retarding or stimulating effect of more than ± 25% compared to the control on day 28 after application.	The reference item had a retarding effect of more than ± 25% compared to the control on days 28 and 97 after application.	Yes

 

RESULTS

The test item had a stimulating and not an inhibiting effect on nitrogen transformation (nitrate-N content, nitrate-N formation rate) of soil microorganisms at test item concentrations of up to and including 640 mg/kg soil dw. The test item concentration of 1000 mg/kg soil dw (corresponding to 411 mg a.i./kg soil dw) inhibited the nitrate formation process (Table 2). Therefore, it can be concluded that the EC50 is between 640 mg and 1000 mg test item/kg soil dw (263.04 – 411 mg a.i./kg soil dw). Statistical analysis resulted in a NOEC (28 d) of 640 mg test item/kg soil dw (263.04 mg a.i./kg soil dw) for the inhibition of nitrogen transformation in soil.

Table 2. Nitrogen Transformation Test: Effects of the test item on Nitrate-N Content and Nitrate-N Rate (mean values)

		Day 0			Day 28			Day 0 - 28
treatment [mg test item (aq. solution)/kg soil dw]	treatment [mg a.i./kg soil dw]	NO3-N [mg/kg dw]	Dev.%^1	sig.^2	NO3-N [mg/kg dw]	Dev.%^1	sig.^2	NO3-N [mg/kg dw]	Dev.%^1	sig.^2
control	Control	18.259	--	--	42.588	--	--	0.869	--	--
80	32.88	17.848	-2.25	n.s.	49.671	16.63	n.s.	1.136	30.72	n.s.
160	65.76	17.881	-2.07	n.s.	50.000	17.40	n.s.	1.147	31.99	n.s.
320	131.52	17.784	-2.60	n.s.	63.879	49.99	n.s.	1.646	89.41	n.s.
640	263.04	17.502	-4.15	*	67.987	59.64	n.s.	1.803	107.48	n.s.
1000	411	16.727	-8.39	*	21.347	-49.88	*	0.165	-81.01	*

¹: Dev., deviation from control

²: sig.: significance to control according to Williams multiple sequential t-test procedure, one-sided smaller, α = 0.05 (* = significant; n.s.: not significant)

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Description of key information

NOEC (28 d) = 263.04 mg a.i./kg soil dw (nominal, OECD 216, soil microorganisms)

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

263.04 mg/kg soil dw

Additional information

There is one GLP study available, in which the toxicity of sodium dimethyldithiocarbamate (CAS 128-04-1) to soil microorganisms was assessed according to OECD guideline 216.

Standard soil F5M, sampled from the Rhineland Palatinate, was enriched with 0.5% lucerne meal (based on soil dry weight), adjusted to 45% Water Holding Capacity and exposed to 80, 160, 320, 640, and 1000 mg test item (aqueous solution)/kg soil dw for 28 d. A negative control (pure water) was run in parallel. The effects on soil nitrogen transformation, i.e. on nitrate nitrogen production (NO3- nitrogen), was determined by measuring NO2- nitrogen and NO3- + NO2- nitrogen contents by continuous flow analysis in soil samples taken after 6 h within test start and after 28 d. The concentrations of nitrate nitrogen production in the soil were then calculated from the measured values by subtracting the nitrite nitrogen concentrations from the nitrate+nitrite nitrogen concentrations.

After 28 d, it was found that the test item had a stimulating and not an inhibiting effect on nitrogen transformation (nitrate-N content and nitrate-N formation rate) by soil microorganisms at test item concentrations of up to and including 263.04 mg a.i./kg soil dry weight. At test item concentrations of 411 mg a.i./kg soil dry weight, the nitrate-nitrogen formation process was inhibited. Therefore, it was concluded that the EC50 lies between 263.04 and 411 mg a.i./kg soil dry weight. Statistical analyses resulted in a NOEC (28 d) of 263.04 mg a.i./kg soil dry weight for the inhibition of nitrogen transformation in soil.