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Ecotoxicological information

Toxicity to terrestrial plants

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Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted on read-across material
Justification for type of information:
See the read-across report attached in Section 13.
Cross-reference
Reason / purpose:
read-across source
Reference
Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted on read-across material
Remarks:
Meets generally accepted scientific standards, well documented. The read-across from MnCl2 to Mn(NO3)2 is justified on the following basis: both substances are very soluble in water hence bioavailable and both will release Mn2+ ions. Therefore, from an ecotoxicity standpoint, the chloride or nitrate anions are not considered to have any influence on the effective toxicity of Mn2+ or any toxicity in their own right, so the anions can be disregarded. Therefore any effect will be related to the Mn2+ cation, and the data from MnCl2 ecotoxicity tests is regarded as a suitable surrogate for read-across
Justification for type of information:
See the read-across report attached in Section 13.
Reason / purpose:
other: Read-across target
Qualifier:
according to
Guideline:
other: ISO 11269-1 (1993):barley root elongation
Principles of method if other than guideline:
The principle of this test is based on the growth of 6 pre-germinated seeds per pot under controlled conditions (16h/8h cycle light/darkness, 20°C during night time, 70% humidity) for a period of 5 days. The endpoint of this assay is the mean length of the longest root of each seedling per pot.
GLP compliance:
yes
Remarks:
K.U.Leuven
Analytical monitoring:
yes
Details on sampling:
- Sampling method: Total metal concentrations in soil were determined after the post-spiking incubation time for both spiked and control soils.
Vehicle:
yes
Details on preparation and application of test substrate:
All soils were air dried at 25°C and sieved to <4mm. Soil samples were pre-incubated at a moisture content equivalent to 50% of pF2 for 7 days at 20°c.Uncontaminated soils were spiked with MnCl2 to seven concentrations (control plus six treatments; 0, 0.01, 0.032, 0.1, 0.32, 1 and 3.2 x CEC;). Added Mn concentrations in corresponding treatments differ between the 3 soils as their CEC values increase from 6 to 21 cmolc/kg. Additional deionised water was added together with the spike solution to adjust the soil moisture content to 75% of pF2.0. All soils were thoroughly mixed after amendments using laboratory spoons. These spiked and pre-incubated soils was used for all microbial assays.
Species:
Hordeum vulgare
Plant group:
Monocotyledonae (monocots)
Test type:
seed germination/root elongation toxicity test
Study type:
laboratory study
Substrate type:
natural soil
Total exposure duration:
5 d
Post exposure observation period:
Not reported
Test temperature:
20°C
pH:
Soil 1- 4.8
Soil 2- 6.3
Soil 3- 7.5
Moisture:
Deionised water was added together with the spike solution to adjust the soil moisture content to 75% of pF 2.0.
Details on test conditions:
TEST SYSTEM
- Test container : Cylinder pots, approximately 8 cm in diameter and 11 cm in height.
- Amount of soil: MnCl2 spiked and pre-incubated soil was divided in 500 g (dry weight basis) subsamples.
- Method of seeding: Seeds with a radical length lower than 2 mm were planted in each pot approximately 10 mm beneath the surface of the soil.
- No. of seeds per container: 6 seeds per pot
- No. of plants (retained after thinning): Not reported
- No. of replicates per treatment group: 3
- No. of replicates per control: 3


SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: Soil 1: Kasterlee (Belgium), Soil 2: Ter Munck (Belgium), Soil 3: Nagyhorcsok (Hungary)
- Collection procedures: Soils were collected from uncontaminated topsoils with contrasting soil properties. Soils were collected with a metal spade from the plough layer.Stones and vegetation were cleared from the soil samples before being put in 60 litre plastic drums.
- Sampling depth (cm): Not reported
- Soil texture (if natural soil)
- % sand: Soil 1- 79%, Soil 2- 8%, Soil 3- 13%
- % silt: Soil 1- 9%, Soil 2- 70%, Soil 3- 54%
- % clay: Soil 1- 9%, Soil 2- 70%, Soil 3- 54%
- Organic carbon (%): Soil 1- 2.8 %, Soil 2- 0.9 %, Soil 3- 2.1 %
- Maximum water holding capacity (in % dry weight): Soil 1 - pF0 -47%, pF1.8 -31, pF2- 27. Soil 2- pF0 -43%, pF1.8 -34, pF2-34. Soil 3-pF0 -48%, pF1.8 -35, pF2- 34
- CEC(at pH soil cmolc/kg): Soil 1-6.3, Soil 2-12.2 , Soil 3-24.8
- Storage : Air dry, sieved soils were stored in 60 litre plastic drums.


GROWTH CONDITIONS
- Photoperiod: 16h/8h cycle light/darkness
- Light intensity and quality: Light intensity at canopy height was 650 µmol photons/ m2/ s
- Day/night temperatures: 20°C during light hours and 16°C during night time
- Relative humidity (%): 70 %

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
The longest root per seedling was measured after 5 days of growth.


TEST CONCENTRATIONS
- Results used to determine the conditions for the definitive study: The rationale behind this spiking procedure (Mn addition as a fraction of the CEC) was based on previous research on metal toxicity in the lab showing strong positive correlations between metal toxicity (ECx values) and soil CEC i.e. soils with high CEC generally have higher ECx values than soil with low CEC. Therefore it was postulated that higher Mn additions were required in soil with high CEC compared to soil with low CEC to have a similar ECx values.
Nominal and measured concentrations:
Soil 1- 0, 17, 55, 170, 545, 1703, 5450 - Added Mn (mg/kg)
Soil 2- 0, 34, 107, 335, 1072, 2251, 10724 -Added Mn (mg/kg)
Soil 3- 0, 68, 218, 681, 2180, 6813, 21800 -Added Mn (mg/kg)
See table 6
Reference substance (positive control):
no
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
NOEC
Effect conc.:
322 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
other: Mn2+
Basis for effect:
other: Root elongation
Details on results:
Not reported
Results with reference substance (positive control):
Not reported
Reported statistics and error estimates:
Dose-response curves were fitted by a log-logistic model (Doelman and Haanstra, 1989) using the Maquardt Method (proc NLIN, SAS® 9.1; Cary, NC, USA):

Y = c/[1 + exp(b(x-a))]

With y = response variable, c= response in the control treatment, b= slope parameter, x= logarithm of the added Mn concentration and a = logarithm of the EC50 value. The model was adjusted to account for hormesis effects (Schabenberger et al., 1999; Van Ewijk and Hoekstra, 1993). The ‘dose’ in this model is the added Mn concentration (nominal concentration); with the dose in the control soil attributed a very small value (e.g. 0.001 mg Mn/kg). The EC50 values and their 95% confidence interval, expressed as added Mo, are predicted from the appropriate parameters of the curve. The EC50 values, expressed as ‘total Mn’, are calculated from the sum of background Mn concentration of a soil and corresponding EC50 (expressed as added Mn). No observed Effect Concentration (NOEC) are the highest Mn concentration in the soil at which no significant adverse effects on plant/ microbial assay were observed compared to the control soil (P> 0.05), and Lowest Observed Effect Concentrations (LOEC) are the lowest Mn concentration in the soil at which a significant adverse effect on plant/ microbial assay were observed compared to the control soil (P<0.05). Significant effects were determined by ANOVA (Dennett’s test). The threshold values (NOEC, LOEC and EC50) were determined in terms of soil Mn (mg/kg).

Table 8.Soil Mn toxicity thresholds for barley root elongation in freshly spiked soils. Thresholds are expressed as added + background Mn and the Confidence Intervals (CI) of EC10 and EC50 are given

 

Soil

Background Mn Conc. (mg/kg)

Root length control soil (cm)

NOEC (mg/kg)

EC10

(mg/kg)

95% CI

EC50 (mg/kg)

95% CI

1

152

14.3

322

497

369-701

965

767-1226

2

461

12.9

796

820

742-920

1239

1081-1438

3

722

9.4

940

1081

1003-1181

1500

1342-1699

Table 9.Root elongation expressed as lengths (cm) in Mn freshly spiked soil

 

Added Mn(mg/kg)

Soil 1

Root Length (cm)

0

14

10.5

13.8

14.2

13.5

14.8

0

14.2

14.5

16

15.5

15

13.5

0

14.5

16

13.4

15.4

13.2

15.1

17

11.8

11

11.5

12.5

14.3

13.2

17

10.4

11.5

12.4

11.8

12

12.5

17

15.2

12.4

14.2

13.5

10.2

1

55

14.5

13

13

12.5

13.7

13.5

55

13.8

12.5

12

12

12

11.5

55

13.5

15

13.5

11

13.5

13.5

170

11.5

13.5

11

15

11.5

12.4

170

12.8

13.2

16

13

14.5

13.5

170

14.8

14.5

16.4

15

14

14.5

545

12

11.2

11.4

12

12.1

12

545

11.7

12.4

11

11.

12.7

11.4

545

7.2

4.5

5

5

5.5

4.8

1703

1.5

1.7

1.8

2

3

1.5

1703

2

1.4

1.5

1.3

2

1.5

1703

2.4

2.3

1.1

1.8

1.2

1.5

5450

0.5

0.8

0.8

0.5

0.6

1

5450

1

1

0.5

0.4

0.3

0.4

5450

1.2

1

1

0.4

0.4

1

 

  10.Root elongation expressed as lengths (cm) in Mn freshly spiked soil.

  

Added Mn(mg/kg)

Soil 2

Root Length (cm)

0

9.5

13.7

13

11

14.5

13.5

0

11

13.2

11

14.5

11.5

15

0

14.5

13

13.2

12

14.2

13

34

15.7

12.7

11.5

14.5

14.8

15

34

10

13

11.2

11

12.2

14

34

14.7

15

13.2

14

11.5

14

107

11.4

12.2

12

11.8

10.8

11

107

12.5

13.8

14.4

13.5

13.4

 

107

13.7

12.8

11.5

11.4

13.5

16

335

11.8

12.7

11.8

12.7

11.2

12

335

12.7

11.1

12.7

11

12.4

11.7

335

12.2

12.5

11.7

10.5

 

8.5

1072

4.8

3.5

4.4

4.4

4.1

3.5

1072

3.8

3.1

4.5

4.5

4

3.5

1072

3

1.2

1.5

1.1

0.5

0.5

3351

1.5

1.7

1.8

2

3

1.5

3351

2

1.4

1.5

1.3

2

1.5

3351

2.4

2.3

1.1

1.8

1.2

1.5

10724

0.5

0.8

0.8

0.5

0.6

1

10724

1

1

0.5

0.4

0.3

0.4

10724

1.2

1

1

0.4

0.4

1

 

Table 11.Root elongation expressed as lengths (cm) in Mn freshly spiked soil.

 

 

Added Mn(mg/kg)

Soil 3

Root Length (cm)

0

9.2

8.7

11

10.1

9.2

9.8

0

8.8

9

9.5

10.5

9.5

6

0

9

9.8

10

10.2

10.2

8.7

68

12.5

11.8

9.2

11

11

11.8

68

10.4

11.8

11

11.5

12.2

10

68

12.4

10.5

11.2

10

11

9.8

218

12.2

9.8

10.5

9

11.1

10.7

218

 13.7

12.5

10.7

11.4

9.5

11

218

12

12.7

11.4

12.7

10.2

 

681

6.7

3.2

3.5

3.7

2.8

2.7

681

3.8

2.7

5

5.1

2.5

2.7

681

6

5.8

5.4

4.4

4

3.7

2180

2.3

3.8

2.5

3.2

3

3.1

2180

2.2

1.7

2.1

1.7

1.7

1.8

2180

3.2

2.5

3.5

3

2.7

3

6813

1.5

1.7

1

1.2

1.1

1.1

6813

1.4

1.4

1.5

1.3

1

1.1

6813

1.2

1.3

1.1

1.5

1.5

1.5

21800

0.4

0.5

0.7

0.3

0.5

0.8

21800

1

1

0.5

0.4

0.3

0.4

21800

1.1

0.7

0.5

0.4

0.4

0.7

Conclusions:
Increasing Mn concentration significantly affected the barley root length in the three soils. The lowest NOEC was 322 mg Mn/kg. The read-across from MnCl2 to Mn(NO3)2 is justified on the following basis: both substances are very soluble in water hence bioavailable and both will release Mn2+ ions. Therefore, from an ecotoxicity standpoint, the chloride or nitrate anions are not considered to have any influence on the effective toxicity of Mn2+ or any toxicity in their own right, so the anions can be disregarded. Therefore any effect will be related to the Mn2+ cation, and the data from MnCl2 ecotoxicity tests is regarded as a suitable surrogate for read-across

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2009
Report Date:
2009

Materials and methods

Test material

Reference
Name:
Unnamed
Type:
Constituent

Results and discussion

Effect concentrations
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
NOEC
Effect conc.:
322 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
other: Mn2+
Basis for effect:
other: Root elongation

Applicant's summary and conclusion