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Toxicity to soil microorganisms

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Description of key information

No adverse effects on the soil carbon and nitrogen transformation (OECD 216 and 217)

Key value for chemical safety assessment

Additional information

Two studies investigating the toxicity of the test item to soil microorganisms are available.

Effects on the activity of soil microflora were investigated in a carbon transformation test by Schulz (2012a). This study was conducted in compliance with GLP and according to the OECD test guideline 217. Isotianil a.s. was used in the test. A loamy sand soil (DIN 4220) was exposed for 28 days to 0.80 and 8.00 mg test item/kg soil dry weight. Application rates were equivalent to 0.6 and 6 kg test item/ha. Determination of carbon transformation in soil was performed after addition of glucose. A respirometer system was used to determine the O2-consumption over a period of maximum 12 hours at different sampling intervals (0, 7, 14 and 28 days after treatment). No adverse effects of Isotianil a.s. on carbon transformation in soil were observed at either test concentrations (0.80 mg/kg dry soil and 8.00 mg/kg dry soil) after 28 days. Even though the 10-fold dose of the test item revealed a statistically significant difference to the control group at the end of the study, the deviation from the control was still below the threshold value recommended by the guideline. Only negligible deviations from control of -2.1% (test concentration 0.80 mg/kg dry soil) and -13.8% (test concentration 8.00 mg/kg dry soil) were measured at the end of the 28-day incubation period. Effects on carbon transformation in soil after treatment with Isotianil a.s. are given in the following table:

Days after application

Control

0.80 mg test item/kg soil d.w. equivalent to 0.6 kg test item/ha

8.00 mg test item/kg soil d.w. equivalent to 6 kg test item/ha

O2 consumption [mg/kg soil d.w./h]

CV [%]

O2 consumption [mg/kg soil d.w./h]

CV [%]

Deviation from control [%]

O2 consumption [mg/kg soil d.w./h]

CV [%]

Deviation from control [%]

0

12.03

2.6

11.99

1.5

-0.3

11.01

1.3

-8.5

7

11.39

0.8

11.52

0.7

+1.2

10.61

1.3

-6.8

14

10.90

1.6

10.78

0.5

-1.1

9.72

1.2

-10.8

28

11.26

1.1

11.02

2.4

-2.1

9.71

1.5

-13.8

Thus, it is concluded that Isotianil a.s. caused no adverse effects (deviation from control <25 %) on the soil carbon transformation (measured as oxygen consumption) at the end of the 28-day incubation period.

In a second study the effects on the activity of soil microflora were investigated in a nitrogen transformation test by Schulz (2012b). This study was also conducted in compliance with GLP and followed the OECD test guideline 216. Isotianil a.s. was used in the test. A loamy sand soil (DIN 4220) was exposed for 70 days to 0.80 and 8.00 mg test item/kg soil dry weight. Application rates were equivalent to 0.6 and 6 kg test item/ha. Determination of the nitrogen transformation (NO3-nitrogen production) in soil enriched with lucerne meal (concentration in soil 0.5 %). NO3- and NO2-nitrogen were determined using the Autoanalyzer (BRAN+LUEBBE) at different sampling intervals (0, 7, 14, 28, 42, 56 and 70 days after treatment). The test item Isotianil a.s. caused a temporary stimulation of the daily nitrate rate at the tested concentration of 0.80 mg/kg dry soil at time interval 7-14 days after application. However, no adverse effects of Isotianil a.s. on nitrogen transformation in soil could be observed at the tested concentration of 0.80 mg/kg dry soil, 28 days after application (time interval 14-28 days). Since in this application rate the deviation from the control

was below ±25% on day 28, no further evaluations were performed. Temporary stimulations of the daily nitrate rate were also observed at 8.00 mg/kg dry soil beginning at time interval 7-14 until time interval 42-56 days after application. However, no adverse effects of Isotianil a.s. on nitrogen transformation in soil could be observed at the tested concentration of 8.00 mg/kg dry at the end of

the test, 70 days after application (time interval 56-70 days). Only negligible differences to control of +3.9% (test concentration 0.80 mg test item/kg dry soil) and +12.8% (test concentration 8.00 mg/kg dry soil) could be observed 28 days (time interval 14-28 days) and 70 days (time interval 56-70 days) after application, respectively. Effects on nitrogen transformation in soil after treatment with Isotianil a.s. are given in the following table:

Time Interval (days)

Application rates

Control

[IST a.s]

0.80 mg/kg dry weight soil

8.00 mg/kg dry weight soil

Nitrate-N

Nitrate-N

% difference to control

Nitrate-N

% difference to control

0-7

1.84

±

0.01

1.72

±

0.11

-6.7

2.04

±

0.24

+10.6

7-14

0.84

±

0.07

1.35

±

0.24

+60.8

1.59

±

0.15

+89.8

14-28

0.55

±

0.00

0.57

±

0.01

+3.9

0.82

±

0.11

+48.7

28-42

0.74

±

0.02

-

±

-

-

1.00

±

0.17

+35.5

42-56

0.36

±

0.07

-

±

-

-

0.48

±

0.22

+32.0

56-70

0.65

±

0.09

-

±

-

-

0.73

±

0.22

+12.8

In conclusion, Isotianil a.s. tested in a field soil at concentrations up to 8.00 mg test item/kg soil (equivalent up to an application rate of 6 kg test item/ha) caused no adverse effects (difference to control < 25%) on the soil nitrogen transformation (measured as NO3-N production) at the end of the 70-day incubation period.