Reaction mass of Limestone and dicalcium silicate

Toxicity to soil microorganisms

Administrative data

Endpoint:

toxicity to soil microorganisms

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

April 18, 2007 - July 25, 2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Rationale for read-across: in the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below: Ca(OH)2 <-> Ca2+ + 2OH- 100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol OH Ca(OH)2 + 2Ca2SiO4 +9CaCO3 + 13H2O <-> 14Ca2+ + 2SiO2 + 9CO2 + 28OH- 100 mg “Reaction mass of limestone and dicalcium silicate” or 0.08 mmol sets free 2.24 mmol OH- has to be noted that CO32- is not expected to directly release two hydroxyl ions under most environmental conditions (depends on CO2 concentrations and pH) and this is therefore a worst case assumption. From these reactions it is clear that the effect of "Reaction mass of limestone and dicalcium silicate" will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for lime (chemical), hydraulic and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of "Reaction mass of limestone and dicalcium silicate" is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to "Reaction mass of limestone and dicalcium silicate" is justified.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2007

Report date:

2007

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Calcium dihydroxide

EC Number:

215-137-3

EC Name:

Calcium dihydroxide

Cas Number:

1305-62-0

Molecular formula:

CaH2O2

IUPAC Name:

calcium dihydroxide

Details on test material:

IUPAC name: Calcium dihydroxide
Product type: PRECAL(R) 50S
Batch no: 7025
Received: 30 January 2007
Purity active ingredient: 98.2% calcium dihydroxide
Chemical analysis: 74.4% CaO, 0.6% MgO, 0.07% SiO2, 0.05% Al2O3, 0.04% Fe2O3, 0.02% Mn3O4, 0.01% SiO3
Air jet sieving: R>90 um 4%; R>200 um 0.1%; R>630 um 0%
Laser particle size distribution: 27.3% <1 um; 50% < 1.7 um; 97% < 50 um
Expiry date: January 2009
Appearance: white powder
Water solubility (20°C): 1650 mg/l
Storage conditions: room temperature, dry conditions

Sampling and analysis

Analytical monitoring:

no

Details on sampling:

SOIL
- on days 0 (3 hours), 14, 28, 48 and 96 after application, soil samples were taken for the determination of the mineral nitrogen content of the soil.

Test substrate

Vehicle:

yes

Details on preparation and application of test substrate:

COLLECTION
- soil removal: to a depth of 20 cm as mixed sample
- dried at room temperature
- passed through a 2 mm mesh sieve
- characterization: biologically active agricultural loamy sand soil (1.42% organic C, 9.9% clay, 39% silt, 51.2% sand), no fertilisation since 2003, last application of plant protection products in 1990
- origin: wassergut Canitz, Germany (12.694435960 degrees East, 51.403774567 degrees North)
STORAGE
- at a temperature of 4 °C
- in aerobic conditions in the dark
- before applicatin soil was adapted to test conditions
PREPARATION
1)
- 300 g soil (dry weight) (= one sub-sample) weighed per test vessel
- soil mixed with 0.5 % lucerne meal (i.e. 1.5 g/300 g soil d.w.) by means of a hand-stirrer
- vehicle: quartz meal
- water was added to the soil to achieve a water content of approx. 55 % of WHC
- incubation in wide-mouth glass flasks (500 mL) the below described test conditions
2)
- an additional soil sample (without lucerne meal) used for determination of initial NH4-N- and NO3-N-content
- NO3-N-content was 0.96 mg/100 g soil d.w.

Test organisms

Test organisms (inoculum):

soil

Study design

Total exposure duration:

96 d

Test conditions

Test temperature:

19.9 - 21.9°C in a climatic room

Moisture:

18.66-19.70 g/100 g soil d.w.

Details on test conditions:

- Illumination: darkness
- 3 replicates per concentrations (i.e. 3 subsamples of soil per concentration)
- humus content of soil: 2.44%
- initial pH 7.1
- microbial biomass 23.55 mg C/100 g soil d.w. (i.e. 1.66% compared to organic C content)

Nominal and measured concentrations:

nominal concentrations: 0, 1, 2, 4, 8, 10 and 12 g test item/kg soil dry weight

Reference substance (positive control):

yes

Remarks:

(Dinoterb)

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

8 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Effect concentrations 2

Duration:

48 d

Dose descriptor:

NOEC

Effect conc.:

10 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Effect concentrations 3

Duration:

96 d

Dose descriptor:

NOEC

Effect conc.:

>= 12 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Effect concentrations 4

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

9.7 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Effect concentrations 5

Duration:

48 d

Dose descriptor:

EC50

Effect conc.:

> 10 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Effect concentrations 6

Duration:

96 d

Dose descriptor:

EC50

Effect conc.:

> 12 g/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: nitrogen transformation

Results with reference substance (positive control):

Dinoterb caused a stimulation of nitrogen transformation of 44.8% and 58.2% at 6.80 and 16.00 mg Dinoterb per kg soil dry weight, respectively, 28 days after application.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Remarks:

(The coefficients of variation in the control group of the nitrogen transformation test were maximum 9.3% and thus fulfilled the demanded range (≤ 15%).)

Conclusions:

The 96d-NOEC was 12 g/kg soil dry weight, the highest concentration tested. The pH of the soil increased with increasing concentrations of calcium dihydroxide. The high pH value of the soil is considered to be the toxic effect. At the highest concentration tested (12 g/kg soil), the maximum pH level was 11.9 which decreased to 8.5 during the course of the study. At high test concentrations, the nitrogen transformation activity of the soil microflora was shown to recover within 100 days of exposure to the test item. At low test item concentrations the nitrogen transformation was stimulated.