Barium sulphide

Adsorption / desorption

Description of key information

BaS will not occur as such in the environment. In the aqueous and terrestrial environment, barium sulfide dissolves in water releasing barium cations and sulfide anions. 
Due to its rapid transformation in the environment, this endpoint is not relevant for sulfide.
Partition coefficients for barium in different environmental compartments (sediment, suspended particulate matter, soil) have been proposed in the RIVM-report (Crommentuyn et al, 1997).
- The value for barium in soil is put forward for exposure and risk assessment purposes.
- For the sediment compartment the typical KD based on FOREGS data is put forward as a reliable value for Europe.
- A value of 1.5 has been proposed as a relevant ratio between the KD for sediment and the KD for suspended matter (Stortelder et al, 1989; Van de Meent et al, 1990), and this ratio was also used by RIVM for setting relevant KD-values for various metals. Application of this factor on the KD,sediment of 3,478 L/kg, results in an estimated KD, part. matter of 5,217 L/kg, or a log KD, part. matter of 3.72. This value is supported by KD values for suspended matter that were reported by Popp and Laquer (1980) for North-American Rivers (range of Log KD:2.65-3.91) and the value derived by Li et al (1984) for the Hudson River (log KD: 3.78).
References:
ATSDR (2006) Toxicological profile for hydrogen sulfide.
Cihacek LJ, Bremner JM. 1993. Characterization of the sulfur retained by soils exposed to hydrogen sulfide. Commun Soil Sci Plant Anal 24:85-92. 
Jørgensen BB. 1982. Ecology of the bacteria of the sulphur cycle with special reference to anoxic-oxic interface environments. Philos Trans R Soc Lond B Biol Sci 298:543-561.
Smith KA, Bremner JM, Tabatalag MA. 1973. Sorption of gaseous atmospheric pollutants by soils. Soil Sci 116:313-319

Additional information

BaS will not occur as such in the environment. In the aqueous and terrestrial environment, barium sulfide dissolves in water releasing barium cations and sulfide anions.

Sulfide anions react with water in a pH-dependant reverse dissociation to form bisulfide (HS^-) or hydrogen sulfide (H₂S), respectively (i.e., increasing H₂S formation with decreasing pH). Sulfides, HS^-and S^2-, and its oxidation products such as sulfate do not have a major potential for adsorption based on their negative charge. Clay or organic matter in soils and sediments may sorb H₂S to a certain extent but because the molecule is not positively charged only weak adsorption resulting from electrostatic attraction between negative binding sites and partially positive parts of the molecule may be observed. The capacities of soil samples to sorb H₂S in a laboratory study by Smith et al. (1973) ranged from 15.4 to 65.2 mg/g soil for air-dried soils, and from 11.0 to 62.5 mg/g soil for moist soils. The sorption was not affected by soil sterilization, indicating that soil microorganisms are not likely to be involved in the sorption process. These values, however, do not provide reliable estimates of soil sorption under natural conditions, where H₂S would be oxidized to sulfate. Cihacek and Bremner (1993) showed that soils can sorb considerable amounts of H₂S from the air, retaining it as elemental sulfur. However, several species of soil, aquatic, and marine microorganisms oxidize hydrogen sulfide to elemental sulfur, and its half-time in these environments usually ranges from 1 hour to several hours (Jørgensen 1982). Thus, it can be concluded that this endpoint is not relevant for sulfide due to its rapid transformation in the environment.

Values for Ba-K_Dfor 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 centre 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 dissolved background concentrations from 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 K_Ds 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 K_Dvalues 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 K_{D, part. matter}value and K_{D, sediment}value of 1,349 L/kg and 1,000 L/kg, respectively.

Bockting et al (1992) also reported K_{D, soil}values for different metals. For Ba, the proposed logK_{D, soil}was 1.78, which corresponds to a K_{D, 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 K_Dof 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 K_D-value can be derived for each country. Typical country-specific log K_Dvalues range from 2.84 to 4.76, with an overall typical value of 3.54 for Europe. This value is relatively close to the value of 3.00 as reported in the RIVM report, which is based on a limited number of data points. A summary of the selected partition coefficients of barium for different environmental compartments is given below

Table.Overview of selected KD-values for barium, and this for different environmental compartments

Compartment	KD-value (L/kg)	Log KD	Reference
Sediment	3,478	3.54	Salminen et al. (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)

Other adsorption coefficient indicated as dimensionless:
- log Kp (solids-water in soil) ,1.78
- log Kp (solids-water in sediment) ,3.54
- log Kp (solids-water in suspended matter) ,3.72