Barium fluoride

Adsorption / desorption

Description of key information

Barium fluoride will not occur as such in the environment. In the aqueous and terrestrial environment, barium fluoride dissolves in water releasing barium cations and fluoride anions. Therefore available data from studies with barium and fluoride are given as indication of the sorption properties of barium fluoride.

For barium a Kp value of 5217 L/kg is determined for suspended matter-water, a Kp value of 3478 L/kg for sediment-water and a Kp value of 60.3 L/kg for soil-water. For fluoride a Koc value of 3.16 is calculated based on a log Kow of -1 in EUSES (in the EU-RAR for hydrogen fluoride a log Kow of -1.4 is suggested). The values of barium will be used in the risk assessment as worst case.

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

1.78

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

3.54

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

3.71

Additional information

Barium fluoride will not occur as such in the environment. In the aqueous and terrestrial environment, barium fluoride dissolves in water releasing barium cations and fluoride anions. Therefore available data from studies with barium and fluoride are given as indication of the sorption properties of barium fluoride.

Barium

Values for Ba-Kd for sediment, suspended matter and soil were reported by the Dutch National Institute for Public Health and the Environment (RIVM, The Netherlands) in their report “Maximum permissible concentrations and negligible concentrations for metals, taking background concentrations into account” by Crommentuyn et al (1997). Results were discussed within the “Peer Review Committee” of the center for Substances and Risk Assessment prior to publication. In this report, partition coefficients for the distribution of metals between particulate matter and water were used to calculate the dissolved background concentrations from the total background concentration in surface water (application of the equilibrium partitioning method). RIVM conducted a literature search, and also found little data on partition coefficients for Ba to soil and sediment.

For sediment and particulate matter, Crommentuyn et al (1997) reported that Bockting et al. (1992) derived log Kds for different metals, including barium, thereby using the methodology that was described in Stortelder et al (1989). The typical log-values that were derived by RIVM for Ba were based on measurements in North American rivers (data in Popp and Laquer (1980) and Li et al, 1984; log Kd values ranging between 2.65 and 3.91), and were 3.13 and 3.00 for particulate matter and sediment, respectively. These values correspond to a Kd,part.matter value and Kd,sediment value of 1,349 L/kg and 1,000 L/kg, respectively.

Bockting et al (1992) also reported Kd,soil values for different metals. For Ba, the proposed logKd,soil was 1.78, which corresponds to a Kd,soil value of 60.3 L/kg. This value is a relevant data point for calcium, but as the complexion properties of Ba-ions are comparable to those for Ca (Smith and Martell, 1976), this value is considered a reliable estimate for the Kd of Ba to soil. It should be noted, though, that the electrostatic adsorption of Ba by soils is somewhat stronger than for Ca.

Data from FOREGS:

The FOREGS Geochemical Baseline Mapping Programs main aim was to provide high quality, multi-purpose environmental geochemical baseline data for Europe. The sampling sites selected for stream water analyses of dissolved metals were typical of locally unimpacted or slightly impacted areas. Consequently, the metal concentrations that are determined in these samples can be considered as relevant baseline concentrations. A total number of 807 water samples were analyzed for Ba by ICP-MS (detection limit 0.0005 µg/L); dissolved barium levels ranged between 4 and 436 µg/L. For the sediment compartment, the amount of analyzed samples was 845, with barium levels ranging between 31 mg/kg and 3,122 mg/kg. Sediment samples were analyzed by ICP-AES, after aqua regia destruction of the sediment samples (aggressive removal of the complete exchangeable fraction). Raw data were sub-categorized per country, and a typical baseline value (i.e., 50^thpercentile or median) of barium in water and sediment were determined for each country. Assuming that the country-specific median values are relevant for both compartments and represent a state of chemical equilibrium, a typical Kd-value can be derived for each country. Typical country-specific log Kd values are situated between 2.84 and 4.76, with an overall typical value of 3.54 for Europe. This value is relatively close to the value of 3.00 that was reported in the RIVM report, but which was based on a limited amount of data points

A summary of the selected partition coefficients of barium for different environmental compartments is given below

Compartment	Kd-value (L/kg)	Log Kd	Reference
Sediment	3,478	3.54	Salminen et la (2005; FOREGS data)
Suspended particulate matter	5,217	3.72	Estimated data (ratio of 1.5 on, Kd,sediment)
Soil	60.3	1.78	Crommentuyn et al (1997)

Fluoride

For the sorption characteristics of fluoride only qualitative data are available.Fluoride in soil is mainly bound in complexes with aluminium, iron or calcium dependent on the pH and the availability of these counter ions. Fluoride binds to clay by displacing hydroxide from the surface of the clay. The adsorption follows Langmuir adsorption equations and is strongly dependent upon pH and fluoride concentration. It is most significant at pH 3–4, and it decreases above pH 6.5. Low affinity of fluorides for organic material results in leaching from the more acidic surface horizon and increased retention by clay minerals and silts in the more alkaline, deeper horizons. Increased amounts of fluoride are released from fluoride salts and fluoride-rich wastes in soils with high cation exchange capacity. This effect is greatest when there were more exchange sites available and when the fluoride compound cation had greater affinity for the exchange material. Fluoride is also shown to be extremely immobile in soil as determined by lysimeter experiments: 75.8–99.6% of added fluoride was retained by loam soil for 4 years and was correlated with the soil aluminium oxides/hydroxides content. Soil phosphate levels may also contribute to the mobility of inorganic fluoride. In sandy acidic soils, fluoride tends to be present in water-soluble forms.

From the data available for fluoride no actual Kd and/or Koc values can be determined. At neutral pH the major part of fluoride retention in soil appears to be a result of formation of complexes. True adsorption of fluoride and consequential formation of equilibrium between soil/sediment and porewater is not expected based on the anionic character of fluoride.Therefore, fluoride is assumed to have low solids-water partitioning coefficients in the different environmental compartments. For pragmatic reasons, for environmental exposure assessment a Koc is calculated based on a log Kow of -1 in EUSES (in the EU-RAR for hydrogen fluoride a log Kow of -1.4 is suggested). When using the QSAR for non-hydrophobics, a Koc of 3.16 is determined.