High-temperature calcination products of diiron trioxide and amorphous silica resulting in a glassy silica matrix

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption, other

Remarks:

monitoring data in water and sediment

Type of information:

other: Calculation of Kp values based on environmental field data

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark

Remarks:

Kp-values are based on reliable field data of concentration levels in water and sediment; no standard guideline test was conducted to generate Kp-values. Kp-values are calculated based on the hypothesis that equilibrium exists between the baseline levels in water and in sediment.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

monitoring data

Type of information:

other: report

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Qualifier:

no guideline required

Principles of method if other than guideline:

Evaluation and summary of high quality environmental geochemical data for Europe, which is provided by the Forum of European Geological Surveys (FOREGS) and the European Geochemical Mapping of Agricultural and Grazing Land Soil (GEMAS), with respect to silicon concentrations in stream water, stream sediment and topsoil, as well as in agricultural soil and grazing land.

GLP compliance:

no

Type of measurement:

other: Geochemical background and ambient silicon concentrations in different environmental compartments across Europe

Media:

other: Natural stream water, stream sediment and topsoil, as well as agricultural and grazing land soils

Details on sampling:

FOREGS and GEMAS data for EU-27 countries plus UK and Norway were considered, i.e. data from non-EEA countries such as Albania, Bosnia and Switzerland were excluded from further analysis.

FOREGS:
- The FOREGS sampling grid was based on GTN grid cells developed for Global Geochemical Baseline mapping. This grid divides the entire land surface into 160 km x 160 km cells covering an area of 4,500,000 km2.
- Sampling methodology, preparation and analysis are described by Salminen et al. (2005).
- FOREGS data for EU-27 countries plus UK and Norway were considered, i.e. data from non-EEA countries such as Albania and Switzerland were excluded from further analysis.
- A total of 795 stream water samples of silicon dioxide and 839 sediment samples of silicon dioxide were processed in the FOREGS-program, including 743 paired samples, i.e. samples with the same coordinates for the sampling location of stream water and sediment.
- The FOREGS dataset reports silicon/silicon dioxide concentrations for 833 topsoil samples sampled on a grid across Europe. A topsoil sample was taken at each site from 0-25 cm (excluding material from the organic layer where present).
- Reported silicon dioxide concentrations were converted into silicon concentrations.
- High quality and consistency of the obtained data were ensured by using standardised sampling methods and by treating and analysing all samples in the same laboratory of each country.

GEMAS:
- Samples from 33 out of 38 European countries were analysed to develop a suitable harmonised geochemical data base for soils. The sampling started in the spring 2008 and the first four months of 2009.
- The whole GEMAS project area of 5,600,000 km2 was divided into a grid with 50 km x 50 km cells.
- To generate harmonised data sets, all project samples were processed by a central sample preparation facility in Slovakia.
- GEMAS data for EU-27 countries plus UK and Norway were considered, i.e. data from non-EEA countries such as Bosnia and Switzerland were excluded from further analysis.
- The GEMAS dataset reports silicon concentrations of 1,867 samples from the regularly ploughed layer (Ap-horizon) of agricultural land (arable land; 0 - 20 cm) and of 1,781 samples from the top layer of grazing land (soil under permanent grass cover; 0 - 10 cm) sampled on a grid across Europe.

FOREGS DATABASE STREAM WATER/SEDIMENT:

- Sampled stream water and sediments cover a wide range of environmental conditions. Water parameters such as pH, hardness and organic carbon concentrations extend over several magnitudes. Silicon water levels range from 0.05 to 33.7 mg/L with 5^th, 50^th and 95^th percentiles of 0.8, 3.7 and 8.7 mg/L, respectively.

- In the sediment, silicon concentrations range from 11,691.1 to 439,586.6 mg/kg with 5^th, 50^th and 95^th percentiles of 161,384.4, 290,875.4 and 385,246.2 mg/kg, respectively (Table 1).

- Taking into account the high quality and representativeness of the data set, the 95^th percentile of 8.7 mg/L can be regarded as representative background concentration for dissolved silicon in European surface waters and the 95^th percentile of 385,246.2 mg/kg as representative background concentration of silicon in European stream sediments.

- Regarding the partitioning of silicon in the water column, stream water/sediment partition coefficients range from 7,056 to 5,290,000 L/kg. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, a European median log K_p value of 4.87 is derived.

Table 1: Water parameters and silicon/silicon dioxide concentrations of stream sediment and stream water and respective partitioning.

	Parameter	#	Unit	Min.	Max.	5^thP	50^thP
water	pH ^1	735 ^2	-	9.80	4.50	8.50	7.70
water	Ca	743	mg/L	0.23	592.00	1.64	42.70
water	Cl	743	mg/L	0.14	4,560.00	0.49	9.32
water	HCO3	741 ^3	mg/L	0.69	1,804.42	5.36	131.67
water	K	743	mg/L	< 0.01	182.00	0.15	1.64
water	Mg	743	mg/L	0.05	230.00	0.46	6.22
water	Na	743	mg/L	0.23	4,030.00	1.00	6.76
water	NO3	743	mg/L	< 0.04	107.00	< 0.04	3.10
water	DOC	741 ^4	mg/L	< 0.50	57.94	0.60	4.79
water	SO4^2-	743	mg/L	< 0.30	2,420.00	1.18	17.10
water	SiO2	743	mg/L	0.10	72.00	1.66	8.00
water	Si ^5	743	mg/L	0.05	33.67	0.78	3.74
sediment	SiO2	743	%	2.50	94.00	34.51	62.20
sediment	Si ^5	743	mg/kg	11,691.13	439,586.58	161,384.39	290,875.37
Partitioning (Kp)	Si (sed/water)	743	L/kg	7,056	5,290,000	26,762	73,789
Log Kp	Si (sed/water)	743	-	3.85	6.72	4.43	4.87

¹ Statistics are based on H⁺ concentrations rather than pH.

² Removal of 2 outliers < pH 4.3 and 6 negative values.

³ Removal of 2 outliers < 0.01.

⁴ Removal of 1 outlier > 70 mg/L and 1 negative values.

⁵ Values converted from SiO₂.

FOREGS DATABASE Background soil concentrations

- Sampled soils cover a wide range of environmental conditions. Soil parameters, including pH and TOC, cover several magnitudes.

- Baseline silicon levels in topsoil range from 6,874.4 to 452,306.5 mg/kg with 5^th, 50^th and 95^th percentiles of 159,055.5, 317,531.2 and 415,680.6 mg/kg, respectively (see Table 2)

- Taking into account the high quality and representativeness of the data set, the 95^th percentile of 415,680.6 mg/kg can be regarded as representative background concentration of silicon in topsoil of EU countries.

Table 2: Concentrations of silicon/silicon dioxide in topsoil samples.

Parameter	Unit	#	Min.	Max.	5^thP	50^thP	95^thP
pH ^1	-	802	7.55	3.38	7.31	5.49	4.28
TOC	%	799	0.07	46.61	0.56	1.72	5.86
SiO2	%	833	1.47	96.72	34.01	67.90	88.89
Si ^2	mg/kg	833	6,874.4	452,306.5	159,055.5	317,531.2	415,680.6

¹ Statistics are based on H⁺ concentrations rather than pH.

² Values converted from SiO₂.

GEMAS DATABASE AGRICULTURAL AND GRAZING LAND SOIL CONCENTRATIONS:

- Silicon levels of agricultural soil range from 11,499.0 to 448,274.0 mg/kg with 5^th, 50^th and 95^th percentiles of 156,447.5, 311,829.0 and 417,708.0 mg/kg, respectively (see Table 3). In grazing land, soil concentrations of silicon range from 7,058.0 to 450,293.0 mg/kg with 5^th, 50^th and 95^th percentiles of 133,489.0, 299,650.0 and 409,396.0 mg/kg, respectively (see Table 4)

Table 3: Agricultural soil concentrations.

Parameter	Unit	Method	#	Min.	Max.	5^th P	50^th P	95^th P
CEC	meq/100g	AAS	1,867	1.80	48.30	6.10	15.80	33.30
pH (CaCl2)	pH	pH-meter	1,867	3.32	7.98	4.14	5.71	7.45
TOC	%	IR	1,854	0.40	46.00	0.70	1.70	5.67
Silicon	mg/kg	XRF	1,867	11,499.00	448,274.00	156,447.50	311,829.00	417,708.00

Table 4: Grazing land soil concentrations.

Parameter	Unit	Method	#	Min.	Max.	5^thP	50^thP	95^thP
CEC	meq/100g	AAS	1,781	2.54	49.88	8.27	17.96	37.74
pH (CaCl2)	pH	pH-meter	1,780	3.26	8.06	4.03	5.38	7.45
TOC	%	IR	1,780	0.41	49.00	0.94	2.80	11.05
Silicon	mg/kg	XRF	1,781	7,058.00	450,293.00	133,489.00	299,650.00	409,396.00

Conclusions:

Representative background or ambient concentrations of silicon/silicion dioxide in environmental compartments are tabulated below.

compartment, unit, concentration (50th P), concentration (95th P)
background stream water, mg/L SiO2, 8.0, 18.6
background stream water, mg/L Si, 3.7*, 8.7*
background stream water sediment, % SiO2, 62.2, 82.4
background stream water sediment, mg/kg Si, 290,875.4*, 385,246.2*
background topsoil, % SiO2, 67.9, 88.9
background topsoil, mg/kg Si, 317,531.2*, 415,680.6*
agricultural soil, mg/kg Si, 311,829.0, 417,708.0
grazing land soil, mg/kg Si, 299,650.0, 409,396.0
* based on measured SiO2.

Based on the FOREGS dataset, the 95th percentile of 8.7 mg/L can be regarded as representative background concentration of dissolved silicon in European surface waters and the 95th percentile of 385,246.2 mg/kg as representative background concentration of European stream sediments. Regarding the respective partitioning between sediment and water, a European median log Kp value of 4.87 is derived.

Based on the FOREGS dataset, the 95th percentile of 415,680.6 mg/kg can be regarded as representative background concentration of silicon in topsoil of EU countries. Representative silicon concentrations (95th percentile) of agricultural and grazing land soil (i.e. ambient levels) amount to 417,708.0 and 409,396.0 mg/kg, respectively, according to the GEMAS dataset.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Unnamed

Year:

2005

Report date:

2005

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

2021

Report date:

2021

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Evaluation of high quality environmental geochemical data for Europe, which is provided by the Forum of European Geological Surveys (FOREGS), with respect to silicon (Si) concentrations in stream water and stream sediment. Baseline levels of silicon in water and sediment were determined in 743 paired sample locations. Assuming equilibrium between both environmental compartments, site-specific partitioning coefficients (Kp) were derived.

GLP compliance:

no

Type of method:

other: field data of baseline levels in water and sediment

Media:

sediment

Test material

Test material information

Constituent 1

Reference substance name:

not applicable

IUPAC Name:

not applicable

Test material form:

other: elemental concentrations

Details on test material:

naturally occuring silicon

Radiolabelling:

no

Study design

Test temperature:

environmental relevant temperatures

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

FOREGS:
- The FOREGS sampling grid was based on GTN grid cells developed for Global Geochemical Baseline mapping. This grid divides the entire land surface into 160 km x 160 km cells covering an area of 4,500,000 km2.
- Sampling methodology, preparation and analysis are described by Salminen et al. (2005).
- FOREGS data for EU-27 countries plus UK and Norway were considered, i.e. data from non-EEA countries such as Albania and Switzerland were excluded from further analysis.
- A total of 795 stream water samples of silicon dioxide and 839 sediment samples of silicon dioxide were processed in the FOREGS-program, including 743 paired samples, i.e. samples with the same coordinates for the sampling location of stream water and sediment.
- Reported silicon dioxide concentrations were converted into silicon concentrations.
- High quality and consistency of the obtained data were ensured by using standardised sampling methods and by treating and analysing all samples in the same laboratory of each country.

Results and discussion

Partition coefficients

Partition coefficients 1

Key result

Phase system:

sediment-water

Type:

log Kp

Value:

4.87 dimensionless

Remarks on result:

other: European median (50th percentile) log Kp

Partition coefficients 2

Key result

Phase system:

sediment-water

Type:

Kp

Value:

73 789 L/kg

Remarks on result:

other: European median (50th percentile) partition coefficient (Kp)

Results: Batch equilibrium or other method

Adsorption and desorption constants:

The monitoring stream water and sediment data show that silicon (Si) concentrations of sediments range from 11,691.1 to 439,586.6 mg/kg, while dissolved Si concentrations in the water column of European stream waters range from 0.05 to 33.7 mg/L. Regarding the partitioning of Si in the water column, stream water/sediment partition coefficients range from 7,056 to 5,290,000 L/kg. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, the 50th percentile log Kp for Si across Europe was determined to be 4.87 (73,789 L/kg, Table below).

Any other information on results incl. tables

Table: Water parameters and silicon/silicon dioxide concentrations of stream sediment and stream water and respective partitioning.

	Parameter	#	Unit	Min.	Max.	5^thP	50^thP
water	pH ^1	735 ^2	-	9.80	4.50	8.50	7.70
water	Ca	743	mg/L	0.23	592.00	1.64	42.70
water	Cl	743	mg/L	0.14	4,560.00	0.49	9.32
water	HCO3	741 ^3	mg/L	0.69	1,804.42	5.36	131.67
water	K	743	mg/L	< 0.01	182.00	0.15	1.64
water	Mg	743	mg/L	0.05	230.00	0.46	6.22
water	Na	743	mg/L	0.23	4,030.00	1.00	6.76
water	NO3	743	mg/L	< 0.04	107.00	< 0.04	3.10
water	DOC	741 ^4	mg/L	< 0.50	57.94	0.60	4.79
water	SO4^2-	743	mg/L	< 0.30	2,420.00	1.18	17.10
water	SiO2	743	mg/L	0.10	72.00	1.66	8.00
water	Si ^5	743	mg/L	0.05	33.67	0.78	3.74
sediment	SiO2	743	%	2.50	94.00	34.51	62.20
sediment	Si ^5	743	mg/kg	11,691.13	439,586.58	161,384.39	290,875.37
Partitioning (Kp)	Si (sed/water)	743	L/kg	7,056	5,290,000	26,762	73,789
Log Kp	Si (sed/water)	743	-	3.85	6.72	4.43	4.87

¹ Statistics are based on H⁺ concentrations rather than pH.

² Removal of 2 outliers < pH 4.3 and 6 negative values.

³ Removal of 2 outliers < 0.01.

⁴ Removal of 1 outlier > 70 mg/L and 1 negative values.

⁵ Values converted from SiO₂.

Applicant's summary and conclusion

Conclusions:

Reliable baseline levels of silicon in 743 pristine water/sediment samples collected across Europe were determined. Sampling and analytical procedures are considered adequate and resulted in reliable data. Assuming equilibrium between the typical concentration in water and sediment, relevant log Kp-values were generated. Data are therefore considered useful for the determination of a relevant partition coefficient for the sediment compartment. FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe. The 50th percentile of silicon concentrations were considered representative and amount to 290,875.4 mg/kg sediment and 3.7 mg/L stream water, respectively, resulting in a log Kp for partitioning of silicon in European sediment/freshwater of 4.87.