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Toxicity to soil microorganisms

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Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: ISO 18187
Version / remarks:
Contact test for solid samples using the dehydrogenase activity of Arthrobacter globiformis
Deviations:
no
GLP compliance:
no
Specific details on test material used for the study:
Na2HAsO4.7H2O
Analytical monitoring:
yes
Remarks:
background concentration and confirmation of nominal concentrations
Vehicle:
no
Details on preparation and application of test substrate:
Test substance added as aqueous solution and mixed with soil
Test organisms (inoculum):
other: Arthrobacter globiformis
Total exposure duration:
2 h
Remarks:
7 day equilibration after spiking prior to testing
Test temperature:
30
Moisture:
LUFA 2.2 - Dystric Cambisol: 20% of WHC
Refesol 05-G: 20% of WHC
Refesol 06-A: 20% of WHC
Ter Munck - Haplic Luvisol: 20% of WHC
Woburn - Dystric Cambisol: 20% of WHC
Zegveld - Histosol: 20% of WHC
Details on test conditions:
LUFA 2.2 - Dystric Cambisol: 1.78% OC
Refesol 05-G: 2.51% OC
Refesol 06-A: 2.75% OC
Ter Munck - Haplic Luvisol: 1% OC
Woburn - Dystric Cambisol: 5.1% OC
Zegveld - Histosol: 21.68% OC

Test in 24 well plates incubated in the dark for 2 h on a horizontal schaker (U=150/min) at a temperature of 30 ± 1 °C.
Nominal and measured concentrations:
Nominal concentrations in all test soils amounted to 0 (negative control), 30, 95 300, 949, and 3000 mg As/kg soil dry weight.
Measured As concentrations are within 20% of nominal values.
Reference substance (positive control):
yes
Remarks:
600 mg benzalkonium chloride/kg soil dry weight
Key result
Duration:
2 h
Dose descriptor:
NOEC
Effect conc.:
30 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
95 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
EC10
Remarks:
EC10 < lowest test dose
Effect conc.:
13.4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
367.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
NOEC
Effect conc.:
95 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 05-G
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
300 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 05-G
Key result
Duration:
2 h
Dose descriptor:
EC10
Effect conc.:
103.5 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 05-G
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
431.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 05-G
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
<= 30 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 06-A
Duration:
2 h
Dose descriptor:
EC10
Remarks:
EC10 < lowest test dose
Effect conc.:
4.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 06-A
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
289.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Refesol 06-A
Duration:
2 h
Dose descriptor:
NOEC
Effect conc.:
95 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Ter Munck
Remarks:
Haplic Luvisol
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
300 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Ter Munck
Remarks:
Haplic Luvisol
Key result
Duration:
2 h
Dose descriptor:
EC10
Effect conc.:
40.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Ter Munck
Remarks:
Haplic Luvisol
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
555.3 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Ter Munck
Remarks:
Haplic Luvisol
Duration:
2 h
Dose descriptor:
NOEC
Effect conc.:
95 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Woburn
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
300 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Woburn
Remarks:
Dystric Cambisol
Key result
Duration:
2 h
Dose descriptor:
EC10
Effect conc.:
112.6 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Woburn
Remarks:
Dystric Cambisol
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
983.2 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Woburn
Remarks:
Dystric Cambisol
Key result
Duration:
2 h
Dose descriptor:
NOEC
Effect conc.:
30 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Zegveld
Remarks:
Histosol
Duration:
2 h
Dose descriptor:
other: LOEC
Effect conc.:
95 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Zegveld
Remarks:
Histosol
Duration:
2 h
Dose descriptor:
EC10
Remarks:
EC10 < lowest test dose
Effect conc.:
10.1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Zegveld
Remarks:
Histosol
Duration:
2 h
Dose descriptor:
EC50
Effect conc.:
460.2 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
other: dehydrogenase activity
Remarks on result:
other: Zegveld
Remarks:
Histosol
Reported statistics and error estimates:
Normality of the data:
checked with Kolmogorov-Smirnov or Shapiro-Wilk's test

Variance homogeneity of the data:
Levene's or Cochran test

NOEC and LOEC:
- In case data of normal distribution, homoscedasticity and a monotone dose-response relationship: Williams' Multiple Sequential t-test
- In case of normal distribution and variance heterogeneinty: one-sided Welch's t-test
- In case of normal distribution and homoscedasticity, but absence of a monotone relationship: Dunnett's t-test
- In case data were not normally distributed, but homoscedastic: Jonckheere-Terpstra test
- In case data were not normally distributed and heteroscedastic: Bonferroni U-test
- In case data were not normally distributed and the dose-response relationship was not monotone: Bonferroni Median test
(α = 0.05)

ECx values were determined with both linear and non-linear regression models
It was checked for the best fit (R2, Chi2, AIC) after performing an F-test to control significance of the dose response relationship
Validity criteria fulfilled:
yes
Conclusions:
The reliable 2-h EC10 or NOEC values for the effect of arsenic to the dehydrogenase activity of Arthrobacter globiformis ranged between 30.0 and 112.6 mg As/kg soil dry weight (based on added As concentrations in soil).
EC10 values were lower than the lowest test dose (30 mg As/kg soil dry weight) in three different soils and therefore their uncertainty was judged too high to consider these EC10 values for derivation of the PNEC.
Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
ISO 14238
Deviations:
yes
Remarks:
soils not immediately used in the test after sampling
Qualifier:
according to guideline
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
GLP compliance:
no
Specific details on test material used for the study:
Na2HAsO4.7H2O
Analytical monitoring:
yes
Remarks:
background concentration and confirmation of nominal concentrations
Vehicle:
no
Details on preparation and application of test substrate:
Test substance added as aqueous solution and mixed with soil
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Remarks:
7 day equilibration after spiking prior to testing
Test temperature:
20
Moisture:
LUFA 2.2 - Dystric Cambisol: 47% of WHC
Refesol 05-G: 40% of WHC
Refesol 06-A: 30% of WHC
Ter Munck - Haplic Luvisol: 55% of WHC
Woburn - Dystric Cambisol: 45% of WHC
Zegveld - Histosol: 50% of WHC
Details on test conditions:
LUFA 2.2 - Dystric Cambisol: 1.78% OC
Refesol 05-G: 2.51% OC
Refesol 06-A: 2.75% OC
Ter Munck - Haplic Luvisol: 1% OC
Woburn - Dystric Cambisol: 5.1% OC
Zegveld - Histosol: 21.68% OC
Nominal and measured concentrations:
Nominal concentrations:
LUFA 2.2 - Dystric Cambisol: 0, 20, 63.3, 200, 632.5, and 2000 mg As/kg soil dry weight
Refesol 05-G: 0, 10, 31.6, 100, 316, and 1000 mg As/kg soil dry weight
Refesol 06-A: 0, 10, 31.6, 100, 316, and 1000 mg As/kg soil dry weight
Ter Munck - Haplic Luvisol: 0, 20, 63.3, 200, 632.5, and 2000 mg As/kg soil dry weight
Woburn - Dystric Cambisol: 0, 20, 63.3, 200, 632.5, and 2000 mg As/kg soil dry weight
Zegveld - Histosol: 0, 20, 63.3, 200, 632.5, and 2000 mg As/kg soil dry weight

Measured As concentrations are within 20% of nominal values.
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
other: LOEC
Effect conc.:
<= 20 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
855.2 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: LUFA 2.2
Remarks:
Dystric Cambisol
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Refesol 05-G
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Refesol 06-A
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 2 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Ter Munck
Remarks:
Haplic Luvisol
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 2 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Woburn
Remarks:
Dystric Cambisol
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 2 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Zegveld
Remarks:
Histosol
Key result
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
58.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Zegveld
Remarks:
Histosol
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
1 711.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
As (added dose)
Basis for effect:
nitrate formation rate
Remarks on result:
other: Zegveld
Remarks:
Histosol
Reported statistics and error estimates:
Normality of the data:
checked with Kolmogorov-Smirnov or Shapiro-Wilk's test

Variance homogeneity of the data:
Levene's or Cochran test

NOEC and LOEC:
- In case data of normal distribution, homoscedasticity and a monotone dose-response relationship: Williams' Multiple Sequential t-test
- In case of normal distribution and variance heterogeneinty: one-sided Welch's t-test
- In case of normal distribution and homoscedasticity, but absence of a monotone relationship: Dunnett's t-test
- In case data were not normally distributed, but homoscedastic: Jonckheere-Terpstra test
- In case data were not normally distributed and heteroscedastic: Bonferroni U-test
- In case data were not normally distributed and the dose-response relationship was not monotone: Bonferroni Median test
(α = 0.05)

ECx values were determined with both linear and non-linear regression models
It was checked for the best fit (R2, Chi2, AIC) after performing an F-test to control significance of the dose response relationship
Validity criteria fulfilled:
yes
Conclusions:
Regarding the effect of arsenic on the nitrifcation rate in six soils, a 28 d LOEC <= 23 mg As/kg soil dry weight was determined for LUFA 2.2 soil, whereas no effects were observed in the five other soils at concentrations up to 1000 or 2000 mg As/kg soil dry weight. Only one reliable EC10 value could be derived for the effect of arsenic on soil the nitrification rate in soil (58.9 mg As/L, based on added As concentrations in soil).

Description of key information

In total, 6 reliable EC10 or NOEC values for chronic arsenic toxicity to soil microorganisms were retrieved from 1 published study report. All data were derived from soils amended with disodium hydrogen arsenate salts. These data cover effects on arsenic on nitrification and dehydrogenase activity in 6 different soils. The reliable NOEC and EC10 values range between 30.0 and 112.6 mg As/kg dw (both values for dehydrogenase activity), expressed based on added elemental As concentrations in soil. All reliable NOEC and EC10 values were taken forward to the derivation of the PNEC according to the statistical extrapolation approach.

In addition, unbounded NOEC values of 52.8 mg As/kg soil (total soil concentration) were retrieved for the long-term effect of arsenic on the soil microbial biomass, ATP content, dehydrogenase activity and nitrification in a sandy cambisol contaminated for 9 years with sodium arsenic salts.

Key value for chemical safety assessment

Additional information