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Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Study period:
03 September, 2008 through 12 January, 2009
Reliability:
1 (reliable without restriction)
Qualifier:
according to guideline
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.21 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
NECTARYL :
Lot Number : 9000751030
Analytical monitoring:
yes
Remarks:
Samples analysed on DAy 0, 7 and 28 for Nitrate determination
Details on sampling:
On Days 0, 7 and 28 triplicate Control, Solvent Control and Test Concentration sample vessels were sacrificed for Nitrate analysis.
Vehicle:
yes
Remarks:
Dimethylformamide
Details on preparation and application of test substrate:
SOIL :
LUFA Speyer 2.3
Organic Carbon Content : 0.98%
pH : 6.4
CEC : 8 mval/100g

Soil Type : Loamy Sand (DIN), Sandy Loam (USDA)

Amounts of test material (1600 and 5000 mg) were each separately dissolved in DMF and the volume adjusted to 10 mL to give 1600 and 5000 mg/10 mL solvent stock solutions. Serial dilutions were made from the 1600 mg/10 mL solvent stock solution to give a 160 mg/10 mL solvent stock solution and from the 5000 mg/10 mL solvent stock solution to give 500 and 50 mg/10 mL solvent stock solutions. An aliquot (1.0 mL) of the 50 mg/10 mL solvent stock solution was added dropwise on to quartz sand (5.0 g) and the solvent allowed to evaporate to dryness in a fume cupboard. The test material/sand combination and an amount of powdered Lucerne-green-grass-meal (2.5 g) was then added to a final bulk soil weight 500 g (dry weight) and thoroughly mixed using a mechanical mixer, prior to the addition of an aliquot (32.2 mL) of water to give the required test concentration of 10 mg/kg with a nominal moisture content of 40 % of the Water Holding Capacity. Similarly, aliquots (1.0 mL) of the 160, 500, 1600 and 5000 mg/10 mL solvent stock solutions were used to prepare the test concentrations 32, 100, 320 and 1000 mg/kg, respectively. The soil for each test concentration was then mixed again to ensure homogeneity prior to sampling nine replicates for incubation. Three vessels were sacrificed for Day 0 analysis and the remaining six vessels incubated, three of which were sampled on Day 7 and three on Day 28.

The Solvent Control soil was prepared by dispensing an aliquot (1.0 mL) of DMF dropwise on to dry quartz sand (5.0 g) and allowing the solvent to evaporate to dryness in a fume cupboard. The sand and powdered Lucerne-green-grass-meal (2.5 g) was then added to a final bulk soil weight 500 g (dry weight) and thoroughly mixed using a mechanical mixer, prior to the addition of an aliquot (32.2 mL) of water to give the required test concentration of 10 mg/kg with a nominal moisture content of 40 % of the Water Holding Capacity. The Solvent Control was then mixed again to ensure homogeneity prior to sampling nine replicates for incubation. Three vessels were sacrificed for Day 0 analysis and the remaining six vessels incubated, three of which were sampled on Day 7 and three on Day 28.

The Control soil was prepared in an identical manner to the Solvent Control soil with the omission of solvent.

Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
21 +/- 1 °C
Moisture:
40 % (+/- 5%) of Water Holding Capacity
Details on test conditions:
Sample Vessels : Glass conical flasks
Weight of Soil : 50 g (dry weight)
Replicates : 9 replicates per treatment level, Blank Control and Solvent Control
Temperature : 21 +/- 1 °C
Light : Darkness

Deionised reverse osmosis water was added on a weight basis on Days 7, 14, 21 and 28, where necessary, in order to maintain the moisture content within +/- 5 % of the initial moisture content.
Nominal and measured concentrations:
The folowing test concentrations were prepared and tested :
10 mg test item/kg (dry weight)
32 mg test item/kg (dry weight)
100 mg test item/kg (dry weight)
320 mg test item/kg (dry weight)
1000 mg test item/kg (dry weight)
Blank Control
Solvent Control
Reference substance (positive control):
no
Key result
Duration:
28 d
Dose descriptor:
NOEC
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: 1000 mg test item/kg (dry weight) was the highest concentration level tested
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: 1000 mg test item/kg (dry weight) was the highest concentration level tested
Details on results:
Statistical analysis of the nitrate concentration values was carried out for the Control and treatment groups and demonstrated no statistically significant decrease between the Solvent Control and all of the test concentrations tested (P> = 0.05), and, therefore, the NOEC was 1000 mg test item/kg (dry weight).
Validity criteria fulfilled:
yes
Conclusions:
The effect of the test item on the nitrogen transformation activity of soil microorganisms was investigated over a 28-day period and gave the following results :

NOEC > or = 1000 mg test item/kg (dry weight)

EC50 > 1000 mg test item/kg (dry weight)
Executive summary:

The effect of the test item on the nitrogen transformation activity of soil microorganisms was investigated over a 28-day period and gave the following results :

NOEC > or = 1000 mg test item/kg (dry weight)

EC50 > 1000 mg test item/kg (dry weight).

Description of key information

The effect of the test item on the nitrogen transformation activity of soil microorganisms was investigated over a 28-day period and gave the following results :

NOEC > or = 1000 mg test item/kg (dry weight)

EC50 > 1000 mg test item/kg (dry weight)

The test soil was a LUFA Speyer 2.3 Loamy Sand (DIN) with an Organic Carbon content of 0.98%.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
1 000 mg/kg soil dw

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