Zinc hexafluorosilicate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

other: evidence from degradation product

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline available

Principles of method if other than guideline:

Publication according to scientific standards.

GLP compliance:

not specified

Details on results (HPLC method):

In fresh water at pH above 5, the free ion is the main fluoride species. At lower pH, the proportion of fluoride ion decreases, while HF2- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom sediments.

Conclusions:

In fresh water at pH above 5, the free ion is the main fluoride species. At lower pH, the proportion of fluoride ion decreases, while HF2- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom sediments.

Reference 2

Endpoint:

adsorption / desorption: screening

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance and its relevant degradation products decompose rapidly

Reference 3

Endpoint:

adsorption / desorption: screening

Type of information:

other: evidence based on degradation product

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline available

Principles of method if other than guideline:

Publication according to scientific standards.

GLP compliance:

not specified

Details on results (HPLC method):

In fresh water at pH above 5, the free ion is the main fluoride species. At lower pH, the proportion of fluoride ion decreases, while HF2- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom sediments.

Conclusions:

In fresh water at pH above 5, the free ion is the main fluoride species. At lower pH, the proportion of fluoride ion decreases, while HF2- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom sediments.

Description of key information

Kp for solid particulate matter and water (Kpsusp): 110000 l/kg (log value: 5.04) (ECB 2008)

Kp for water and sediment (Kpsed); 73000l/kg ( log value:4.86) (ECB 2008)

Kd for marine waters is 6010 l/kg (log value: 3.78)

Kd for solids-water in soil is 158.5 l/kg (log value: 2.2)

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

4.86

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

2.2

at the temperature of:

20 °C

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

5

at the temperature of:

20 °C

Additional information

The substance decomposes under environmental conditions to zinc ions, silic acid and fluorid (Refer to read-across justification for further details)

Fluoride reacts with phosphates to insoluble fluoroapatite and transferred to sediment. Silic acid reacts to numerous silicates and is ubiquitous in the environment, commonly referred to as Dissolved silica(DSi).

In fresh water at pH above 5, the free ion is the main fluoride species. At lower pH, the proportion of fluoride ion decreases, while HF2- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom sediments. (EU RAR hydrogen fluoride)

For metals, adsorption/desorption translates in the distribution of the metals between the different fractions of the environmental compartment, e.g. the water (dissolved fraction, fraction bound to suspended matter), soil (fraction bound or complexed to the soil particles, fraction in the soil pore water,...).This distribution between the different compartments is translated in the partition coefficients between these different fractions. Study records on partition coeficients are given under 5.6.

Partition coefficients for zinc in freshwater has been reviewed in the RAR (ECB 2008). Based on the extensive experimental evidence, a partition coefficient for the distribution between solid particulate matter and water (Kpsusp) of 5.04 (log value) has been defined for EU waters and used throughout the RAR.

The Kp for the distribution between sediment and water (Kp_sed) was estimated in the RAR from that for particulate matter, as follows: Kp_sed= Kp_susp/ 1.5, based on the average difference in concentrations of zinc and other metals in both media. For zinc this results in a Kp_sedof 73,000 l/kg. (ECB 2008)

The marine Kd was derived based on data from several marine waters. the geomean value for zinc in seawater is 6010 l/kg

For soil, a solids-water partitioning coefficient of 158.5 l/kg (log value 2.2) was determined experimentally on 11 American soils. This value was used in the RA Zinc.

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