Magnesium diniobate

Adsorption / desorption

Link to relevant study record(s)

Reference

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.

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 magnesium (Mg) concentrations in stream water and stream sediment. Baseline levels of magnesium in water and sediment were determined in 745 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

Radiolabelling:

no

Test temperature:

environmental relevant temperatures

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).
- A total of 808 stream water samples and 852 sediment samples were processed in the FOREGS-program, including 757 paired samples, i.e. samples with the same coordinates for the sampling location of stream water and sediment that are summarised below. However, Mg concentrations in 12 stream water samples (3 from Albania and 9 from Switzerland) were excluded from the analysis, resulting in a total of 745 paired samples summarised below.
- 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.

Key result

Phase system:

sediment-water

Type:

log Kp

Value:

2.96 L/kg

Remarks on result:

other: European 50th percentile log Kp

Adsorption and desorption constants:

The monitoring stream water and sediment data show that Mg concentrations of sediments range from 0.1 to 25 %, while dissolved Mg concentrations in the water column of European stream waters range from 0.1 to 230 mg/L, showing a high exchange of Mg between both environmental matrices. Regarding the partitioning of magnesium in the water column, stream water/sediment partition coefficients range from 13 to 339,208 L/kg. Country-specific stream water/sediment partition coefficients are reported in Table 1 with 50th percentile log Kp values ranging from 1.12 to 5.53 L/kg. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, the 50th percentile log Kp for magnesium across Europe was determined to be 2.96 L/kg (Table 2).

Table 1: Country-specific stream water/sediment partition coefficients (log Kp)

Country	# of data	Area (km^2)	Min	Max	Mean	5^thP	50^thP	90^thP	95^thP
AL	3	28,748	2.75	3.15	3.04	2.80	3.13	3.15	3.15
AT	20	83,879	2.07	4.22	3.62	2.19	3.53	3.90	3.96
BE	5	32,545	1.88	3.10	2.71	2.00	2.69	2.99	3.05
CH	9	41,285	2.71	4.25	3.66	2.76	3.04	4.06	4.17
CZ	10	78,866	2.26	3.66	3.13	2.44	2.99	3.44	3.56
DE	74	357,121	1.91	4.23	3.07	2.25	2.72	3.38	3.55
DK	5	43,098	1.87	2.15	2.01	1.88	2.03	2.11	2.13
EE	11	45,227	1.23	3.41	2.65	1.34	2.32	2.85	3.21
ES	85	504,645	1.72	4.16	3.34	2.30	2.96	3.72	3.98
FI	63	338,144	2.25	4.45	3.86	3.20	3.77	4.13	4.26
FR	118	543,965	1.22	3.98	3.05	1.68	2.64	3.47	3.64
GR	27	131,957	2.63	3.78	3.33	2.76	3.24	3.64	3.67
HR	10	56,542	2.28	2.96	2.60	2.30	2.51	2.84	2.90
IE	10	70,273	1.84	4.31	3.85	2.56	3.51	4.24	4.28
IT	45	301,336	1.52	5.00	3.76	1.87	2.99	3.94	4.44
LT	14	64,589	2.24	3.13	2.78	2.32	2.71	3.01	3.06
LV	7	65,301	2.63	3.02	2.83	2.68	2.80	2.94	2.98
NL	9	41,526	1.79	3.05	2.71	1.91	2.64	3.01	3.03
NO	58	323,759	2.30	5.53	4.48	2.88	4.07	4.79	4.97
PL	56	312,685	1.12	3.13	2.08	1.34	1.66	2.43	2.60
PT	19	92,345	1.94	4.28	3.60	2.43	3.22	3.97	4.13
SE	20	449,964	3.11	4.08	3.72	3.11	3.72	3.94	3.98
SK	15	49,034	2.20	3.53	3.01	2.22	2.89	3.37	3.44
SL	4	20,253	3.10	3.47	3.33	3.14	3.34	3.45	3.46
UK	60	219,331	1.16	4.76	3.67	1.91	3.08	4.01	4.28

Table 2: Concentrations of magnesium in sediment and water and resulting partition coefficients

	Concentration		Concentration		Partitioning (Kp)		Log Kp
Parameter	Mg (sediment)		Mg (water)		Mg (sed / water)		Mg (sed / water)
#	757	745^1	757	745^1	757	745^1	757	745^1
Unit	mg/kg		mg/L		L/kg		-
Min.	301.52	301.52	0.05	0.05	13.05		1.12
Max.	14,7743.82	147,743.82	230.00	230.00	339,207.75		5.53
Mean	10,508.92	10,456.40	11.69	11.70	4,829.43	4,847.65	3.00	2.99
STDEV	15,678.36	15,716.86	19.55	19.65	17,187.37	17,312.88	0.78	0.79
5^thp	301.52	301.52	0.46	0.46	43.93	42.88	1.64	1.63
50^thp	7,236.43	6,633.40	6.25	6.24	947.18	912.16	2.98	2.96
90^thp	19,538.37	19,297.15	26.53	26.23	10,006.33	9,879.33	4.00	4.00
95^thp	29,669.37	28,222.08	38.11	38.63	17,898.84	18,394.78	4.25	4.26

¹Values from Switzerland and Albania are not included.

Conclusions:

Reliable baseline levels of magnesium in pristine water/sediment samples were determined in 745 samples. 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 log Kp for the sediment compartment. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, the 50th percentile concentrations of magnesium across Europe were 6,633 mg/kg sediment and 6.24 mg/L stream water, respectively, yielding a log Kp for magnesium across Europe of 2.96.

Description of key information

Magnesium is highly mobile under all environmental conditions and occurs in solution as dissociated Mg2+ ions. A European median log Kp value of 2.96 is derived for sediment-water partitioning. Magnesium is expected to also be highly mobile in suspended matter and soil.

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

2.96

Additional information

The assessment of the partitioning of Mg in freshwater sediments media is based on Kp values derived from monitoring data for elemental Mg concentrations in water and corresponding sediments provided by the FOREGS Geochemical Baseline Mapping Programme that aimed to provide high quality, multi-purpose homogeneous environmental geochemical baseline data for Europe. A total of 745 paired samples, i.e. samples with the same coordinates for the sampling location of stream water (filtered to < 0.45 µm) and sediment (wet sieved in the field to <0.15 mm) were processed (Salminen et al. 2005) and results correspond to steady-state conditions of Mg, independent of Mg speciation.

Sampled stream water and sediments cover a wide range of environmental conditions. Water parameters such as pH, hardness and organic carbon concentrations cover several magnitudes. Magnesium concentrations of sediments range from < 0.1 % to > 10% with 5^thand 95^thpercentile of 0.03 and 2.82 %, respectively, whereas dissolved Mg concentrations in the water column of European stream waters range from < 0.1 to > 200 mg/L with 5^thand 95^thpercentile 0.46 and 38.63 mg/L, respectively.

Regarding the partitioning of Magnesium in the water column, stream water/sediment partition coefficients range from 13.05 L/kg to 339,207.75 L/kg. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, a European median log Kd value of 2.96 is derived for sediment-water partitioning.