O,O,O-triphenyl phosphorothioate

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:

2016-2017

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)

Deviations:

yes

Remarks:

The test system (soil) was stored outside the required range of 4 ± 2 °C at 5.7 to 6.6 °C. The mean value was 6.1°C. An influence to the test result due to this deviation can be excluded.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

yes

Remarks:

Acetone, evaporated before test start

Details on preparation and application of test substrate:

AMENDMENT OF SOIL
- Type of nitrogen source: Luzerne green gras meal (Tock GmbH Futtermühle, 66798 Wallerfangen-Ihn, Germany)
- Crude protein: 17%
- Carotene: 80mg/kg
- carbon content: 41.9g/100g
- nitrogen content: 2.4g/100g
- C/N ratio: 17/1
size: dried and pulverized

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: defined amount of test substance was weighed in a 50 mL volumetric flask, mixed with acetone until the test substance was diluted. Then the flask was filled up to the mark. The mixture appears clear, colorless and dissolved.
The required amounts of the test substance stock solution for each test concentration were taken from the stock solution (prepared at 18 Oct 2016) and mixed with quartz sand as carrier. The volume difference of the aliquots to 10 mL stock solution was regarded and accordingly completed with acetone. Then the organic solvent was removed by evaporation. The aliquots/quartz sand mixture were mixed with the soil.

VEHICLE:
- Chemical name of vehicle (organic solvent): acetone
Based on the specified water solubility the application of the test substance via an aqueous stock solution was not possible because the water solubility is not high enough to prepare a sufficient stock solution with deionized water. The test substance was soluble with acetone. Therefore the addition with a carrier was selected as application method. The carrier, loaded with the test substance aliquots can evenly distributed in the test system.
- Evaporation of vehicle before use: yes

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

19.8-21.1°C

Moisture:

40% of the WHCmax

Details on test conditions:

TEST SYSTEM
- Test container (type, material, size): 2L glass container covered with a perforated aluminium lid
- Amount of soil: 1165g (prepared soil with luzerne meal) + 5g quartz sand
- No. of replicates per concentration, control, vehicle control: 1


SOIL INCUBATION
The first portion of the prepared soil with luzerne meal was mixed with quartz sand without test substance (BC). The second portion of the prepared soil with luzerne meal was mixed
with quartz sand/acetone mixture without test substance (BC solv.). Five portions of the same soil were mixed with the stock solution aliquots/quartz sand mixture (TS1-TS5). The
blending of the test mixtures was done with a mixer.
At start of exposure the 2 L glass test assays were filled with 928 ± 0.5 g of the test mixtures (~ 800 g Dw) and closed with a perforated aluminum cap. The test assays were incubated
in the dark for 28 days respectively at a temperature of 19.8 – 21.1 °C. During exposure, the test vessels were weighed in order to control the water content for seven times. The loss
of weight in the test assays was corrected with deionized water. There were no observations during the incubation of the test vessels and during the measurement of the nitrate content.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
SOIL:
- type: 5M
- Source: Batch: F5M 3516, sampling date 30 Aug 2016 (sunshine air temperature of 30°C) 250 kg 20cm depth, arrival in test facility: 15 Sep 2016
- preparation of soil by the supplier: Drying for 1 day at room temperature, Pre-sieving with 10 mm screen, Last sieving 2 mm screen, water content 6.4 g/100 g dry weight, dry weight 94.0 %
- supplier: Landwirtschaftliche Untersuchungs- und Forschunganstalt Speyer, 67346 Speyer, Germany
- organic carbon: 1.02+-0.08%
- Nitrogen content: 0.13 +-0.01%
- Sand (particle size > 0.063 - 2.0 mm): 54.4 +- 4.0% (German DIN)
- soil type according to German DIN: Loamy sand (IS)
- pH-value: 7.3
- Cation exchange capacity: 17.7 meq/100g
- Maximal water holding capacity: 40.1 ± 2.4 g/100g
- Grain size: 2 mm
- Plant cover: Meadow for the last 5 years (within 2016)
The soil was not treated with crop protection products for more than 4 years. The sampling field was not cultivated for 4 years and no fertilizer application was performed during the last 4 years before sampling the soil.
- water content at test facility: 6.1/100g dw
- initial microbial biomass at test facility: 494.8 carbon/kg dw (= 4.9% of carbon content of the soil)
- storage at test facility: in a cold storage room in a closed plastic bag at a temperature from 5.7 to 6.6 °C the mean value was 6.1°C. This was outside the specified range of 2-6°C.

PREARRANGEMENT:
Two days before start of exposure 8488.2 g of the soil were mixed with 792mL deionized water (the resulting water content corresponds to 40 % of the water holding capacity). The mixture was stored in a laboratory room at room temperature until usage. 40 g luzerne meal was added to the watered soil at the start of exposure.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- nitrate content: start of exposure and after 7, 14, 21, 28 days

VEHICLE CONTROL PERFORMED: yes

Nominal and measured concentrations:

62.5 mg/kg, 125 mg/kg, 250 mg/kg, 500 mg/kg and 1000 mg/kg soil dry weight. The dilution factor was 2.
Additionally soil without test substance as blank control and soil without test substance but with solvent as blank solvent control.

Key result

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

> 275.7 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

nitrate formation rate

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Details on results:

The test batches remained visually unchanged during exposure period. The coefficient of variation in the replicates of the blank solvent control at the end of the
exposure was 1.9 %. The results in this study are consistent with the validity criteria and the test is valid according to the guidelines of this study.

The moistness, pH and temperature were within acceptable guideline specifications.

Validity criteria fulfilled:

yes

Description of key information

EC10(28d) > 275.7 mg/kg soil dw (nominal, active ingredient) for inhibition of nitrogen formation (OECD 216)

Additional information

One study is available investigating the toxicity of O,O,O-triphenyl phosphorothioate in a lower purity (purity > 25%) to soil microorganisms. The study was performed according to OECD guideline 216 and in compliance with GLP criteria (BASF 2016). In this 28-day toxicity study, natural soil was exposed to the test substance at nominal concentrations of 0 (control), 62.5, 125, 250, 500 and 1000 mg/kg (dry weight) under conditions in accordance with the guidelines. The amount of nitrate formed by microbial processes was determined at start of exposure, after 7, 14 and after 28 days at the end of exposure. The results of the nitrate analyses of the treated replicates were compared to control assays and the nitrate production in the treated replicates was expressed as an inhibition of the process of nitrogen oxidation. No adverse effects were observed. Thus, the 28d-EC10 is determined to be > 1000 mg test substance/kg soil dw and > 275.7 mg a.i./kg soil dw based on nominal concentrations.