Magnesium chloride

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Remarks:

other: Monitoring study

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

Sediment samples are collected from three sites at two rivers near Hanoi, Vietnam, at three depths (0-10, 10- 20 and 20-30 cm). Pore water is extracted and filtered through a 0.45 μm nylon filter.
Sediments are then totally digested using a closed vessel microwave system.
Metal contents (in both pore water and digested sediment) are measured by ICP-MS.
Distribution coefficients (logKd) were calculated as the ratio between sediment (mg/kg d.w.) and pore water (mg/L) concentrations.

GLP compliance:

no

Type of method:

other: monitoring study

Media:

sediment

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material :
Magnesium chloride is readily dissociated into magnesium and chloride ions in water. Hence, data from soluble Mg ions can be used in a read-across approach for Magnesiumg Chloride.

Radiolabelling:

no

Test temperature:

20 °c

Details on study design: HPLC method:

HPLC method is not the appropriate method for inorganic substances.

Analytical monitoring:

yes

Details on sampling:

Sediment samples were collected from three sites in both rivers; using a stainless steel Kajak core sediment sampler requipped with a polymethylmethacrylate (PMMA) inner liner with an inner diameter of 46 mm (KC Denmark). Three replicates were collected from each site. The collected waterlogged sediment samples were immediately closed with a lid and stored in a cool box until return to the laboratory where the sediment samples were stored at 4 °C for a maximum of one and a half days until further treatment.

Details on matrix:

Details on samples collection (e.g. location, depth, contamination history, procedure:
- Location : Sediment samples were collected from the To Lich and Kim Nguu rivers, both of which receive wastewater from urban Hanoi (Vietnam).
- Depth : 0 to 30 cm
- Contamination history : Sediment samples were collected from the To Lich and Kim Nguu rivers, both of which receive wastewater from urban Hanoi. Hanoi covers an area of 921 km2 and had a population of 3.1 million people in 2004 (HSO, 2005). Out of the capital’s 274 large scale industries, 68 are considered heavy polluters and a further 4340 smaller industries discharge wastewater of unknown quality. The discharge per day of wastewater was estimated at a total volume of 458 000 m3, 41% of which was of domestic origin, 57% of industrial origin and 2% from hospitals. Only about 4% of the wastewater is subjected to treatment before discharge.
- Storage conditions: The collected sediment samples were immediately closed with a lid and stored in a cool box until return to the laboratory where
the sediment samples were stored at 4 C for a maximum of one and a half days until further treatment.
- pH at time of collection: The pH was 7.4-8.1 in the pore water extracted from the upper 10 cm sediment in the two rivers.
- Organic carbon (%): The organic carbon concentrations were 1.2-5.3% and 1.8-10.6% in the To Lich and Kim Nguu rivers, respectively.
- Redox potential (mv) initial/final: The redox potential in the pore water samples were -257 to -185 mV.

Details on test conditions:

TEST SYSTEM
- Type, size and further details on reaction vessel:
- Water filtered (i.e. yes/no; type of size of filter used, if any): yes. Water samples were filtered through a 0.45 mm nylon filter (Millipore)
- Number of reaction vessels/concentration: 3 replicates were collected from each site (1 concentration / per site)
- Measuring equipment: ICP-MS

Initial conc. measured:

>= 5 138 - <= 9 902 mg/kg sediment d.w.

pH:

8.2

Temp.:

20

Computational methods:

Adsorption and desorption coefficients (Kd): calculated as the ratio between sediment (mg/kg d.w.) and pore water (mg/L) concentrations.

Type:

Kd

Value:

234.4

Temp.:

20 °C

% Org. carbon:

1.2

Type:

Kd

Value:

1 819.7

Temp.:

20 °C

% Org. carbon:

10.6

Details on results (HPLC method):

HPLC methods is not the appropriate method for the determination of inorganic sucstance. Magnesium concentration in pore water and sediment were determined by inductively coupled plasma mass spectroscopy (ICP-MS).

Adsorption and desorption constants:

no information available

Recovery of test material:

no information available

Concentration of test substance at end of adsorption equilibration period:

no information available

Concentration of test substance at end of desorption equilibration period:

no information available

No guideline study, but well performed and well described.

Conclusions:

Observed distribution coefficients (logKd) for Magnesium were determined from monitoring data. Kd values were calculated as the ratio between sediment (mg/kg d.w.) and pore water (mg/L) concentrations for various elements (including Mg).
The study, reports Kd values for sediment ranging between 234 and 1820 L/kg for magnesium.

Executive summary:

Sediments samples were collected from from three sites in both Vietnamese rivers, both of which receive wastewater from urban. Samples were collected with a stainless steel Kajak core sediment sampler equipped with a polymethylmethacrylat inner liner with an inner diameter of. The collected sediment samples were immediately closed with a lid and stored in a cool box until return to the laboratory where the sediment samples were stored atfor a maximum of one and a half days until further treatment. In the laboratory sediment core samples were subdivided into the sections 0 - 10, 10 - 20 and 20-and pore water extracted. Sediment from the depth of 0 was transferred to a polypropylene buchner funnel with a mesh nylon filter and a minimum of 15 ml pore water was extracted under suction. Pore water samples were filtered through a nylon filter and acidified with 0.1 ml 70% HNO3, and stored prior the determination of concentrations of 33 elements.

 

In the other hand, sediment samples were dried at, until no further weight loss occurred then passed through a stainless steel sieve and pulverized in an agate mortar. About 0.25g dry sediment was then totally digested using a closed vessel microwave system.

Distribution coefficients were calculated as the ratio between sedimentand pore water concentrations.

The study, reports Kd values for sediment ranging between 234 and 1820 L/kg for magnesium. An average log Kp of 2.82 L/kg dw was selected for the chemical safety assessment. 

Description of key information

Key study from Marcussen et al. (2008) reported Kd values for sediment ranging between 234 and 1820 L/kg dw, based on monitoring data. Sediment samples were collected from three sites at two rivers near Hanoi, Vietnam, at three depths (0-10, 10-20 and 20-30 cm). Pore water was extracted and filtered through a 0.45 μm nylon filter. Sediments were totally digested using a closed vessel microwave system. Metal content was measured by ICP-MS.

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

2.82

at the temperature of:

20 °C

Additional information

There are 2 studies with relevant information on adsorption/desorption, reporting distribution coefficients (Kd values, i.e. ratio of Mg concentration in solid phase over Mg concentration in solution phase) for sediments. Only one study (Marcussen et al., 2008), reporting Kd values for sediment ranging between 234 and 1820 L/kg, based on monitoring data, is judged reliable (Klimisch 2 - No guideline study, but well performed and well described). The Kp values are based on the measurement of elemental Mg in river sediment and corresponding pore water. An average log Kp of 2.82 L/kg dw was selected for the chemical safety assessment. The selected Kp value for sediment is also used as a screening approach for the Kp in soils and suspended matter. The other study (Routh et al. 1996) is considered as unreliable (Klimisch 3) since no paired observations of Mg concentrations in solid and solution phases were made.

All the information available is based on measurement of elemental Mg in sediment and water and these results can be used for Magnesium Chloride (Magnesium chloride is readily dissociated into magnesium and chloride ions in water).