Strontium sulphide

Adsorption / desorption

Description of key information

SrS will not occur as such in the environment. In the aqueous and terrestrial environment, strontium sulfide dissolves in water releasing strontium cations and sulfide anions. 
Due to its rapid transformation in the environment, this endpoint is not relevant for sulfide.
Partition coefficients for different environmental compartments (sediment, suspended particulate matter, soil) have been derived for strontium, based on literature data and on data generation in the FOREGS monitoring survey.
- The value for soil is the geometric mean of three data points, and is 157.03 L/kg (logKD 2.20)
- For the sediment compartment the typical KD based on FOREGS data is put forward as a reliable value for Europe, i. e., 861.2 L/kg (logKD 2.94).
- A value of 1.5 has been proposed as a relevant ratio between the Kd for sediment and the KD for suspended particulate 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 861.2 L/kg, results in an estimated Kd, suspended mater of 1,291.8 L/kg (logKD 3.11).

Additional information

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

Sulfide: 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.

Strontium:

Sediment compartment

Literature data:

Five literature values reporting KD-values for strontium in sediment were identified, and ranged from 27 to 117.4 L/kg (see table below). These values were used for the determination of a typical Sr-KD-value for the sediment compartment. The geometric mean of the reported KD values was applied to derive this typical sediment KD since all the reported data are considered to be of equal quality, and a KD value of 40.04 L/kg was obtained. The sediments used in the reviewed studies were mainly sandy sediments. The weaker strontium sorption by sand compared to clay, silt or organic matter results in a relatively low KD value.

Table: Overview of partition coefficient between the water and sediment compartment

Reference	KD-value
Bunde et al (1997)	31.5 (log KD: 1.50)
Bunde et al (1998)	58.36 (log KD: 1.77)
Hemming et al (1997)	17.67 (log KD: 1.25)
Kaplan et al (2000)	27 (log KD: 1.43)
Liszewski et al (2000)	117.40 (log KD: 2.07)
Geometric mean:	40.04 (log KD: 1.60)

In a further study, the partition coefficient of water and marine sediment was calculated (Caroll et al, 1999), and a KD for the marine sediment of 75.76 L/kg (log KD: 1.88) was determined using the data of the study.

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 808 water samples were analyzed for strontium by ICP-OES (detection limit 1 µg/L); dissolved strontium levels ranged between 1 and 13,600 µg/L. For the sediment compartment, the amount of analyzed samples was 852, with strontium levels ranging between 31 mg/kg and 1,3522 mg/kg dw. Sediment samples were analyzed by ICP-XRF (X-ray fluorescence; detection limit of 1 mg/kg dw). Raw data were sub-categorized per country, and a typical baseline value (i. e., 50^thpercentile or median) of strontium in water and sediment were determined for each country, respectively. 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 range from 2.57 to 4.35, with an overall median value of 2.94 for Europe (i. e., 861.2 L/kg).

Soil compartment

The performed literature review and data analysis on strontium partitioning coefficients for the sediment compartment also resulted in some KD-values that were more relevant for soil particles. The geometric mean of the reported KD values was taken to derive a typical soil KD since all the reported data are considered to be of equal quality. As such a KD value of 157.03 L/kg is obtained.

The table below gives an overview of the different relevant KD-values that were selected for the derivation of a typical soil-partition coefficient.

Table: Overview of partition coefficient between the water and soil compartment

Reference	KD-value
Bunzl and Schimmack (1989) - E-horizon	44 (log KD: 1.64)
Kami-Ishikawa and Tagami (2008) upland soil	220 (log KD: 2.34 )
Kami-Ishikawa and Tagami (2008) upland soil	400 (log KD: 2.60)
Geometric mean	157.03 (log KD: 2.20)

Conclusion:

For the sediment compartment, two values were identified, i. e., a literature value of 40.04 L/kg based on a limited data set (n=5) and the value of 861.2 L/Kg which was derived for with the data generated in the FOREGS monitoring survey (Salminen et al, 2005).

The latter value was put forward as a typical value for the sediment compartment: literature data were primarily relevant for sandy soils which have a low affinity for metals due to their low clay and organic matter content; therefore they are not representative for silty, loamy and clayey soils.

FOREGS data represents a large amount of samples (>800) representing the whole of Europe; and strontium levels in water and sediment were determined in a uniform way.

Based on the data provided inCrommentuyn et al (1997)it can be concluded that the sediment KD of cationic metals (e. g., Ba, Be, Cd, Co, Cu, Pb, Ni, Zn) is always at least one order of magnitude higher than the soil KD, with differences up to 3 orders of magnitude. Taking into account that literature KD-values for soil were situated between 44 and 400 L/kg, a sediment KD of 40.04 L/kg (based on literature data) would be unlikely.

No data were identified for particulate suspended matter. A partition coefficient for this compartment, however, can be estimated, based on the partition coefficient for sediment which is increased by a factor of 1.5 (Stortelder et al, 1989; Van de Meent et al, 1990) to account for the weaker adsorption of sediments as compared to particulate matter (DBW/RIZA, 1989): the relatively strong adsorption of metals by particulate matter is probably related to the relatively high organic matter and clay content (size fraction < 2 µm).Bockting et al (1992) indicated that this factor of 1.5 remains an assumption and use of this value should be dome with caution.

According to this methodology, a KD, spm of 1291.8 L/kg (i. e., log KD, spm of 3.11) is derived for this compartment.

For the soil compartment the geometric mean of three literature data points is put forward as a typical value for the Sr-KD for soil, i. e., 157.03 L/kg (log KD: 2.20)

A summary of the KD-values for the different environmental compartments is given below:

Compartment	Kd-value (L/kg)	Log Kd	Reference
Sediment	861.2	2.94	Salminen et al (2005; FOREGS data)
Suspended particulate matter	1,291.8	3.11	Estimated data (ratio of 1.5 on KD,sediment)
Soil	157.03	2.20	Bunzl and Schimmack (1989);Kami-Ishikawa and Tagami (2008)

References:

Crommentuyn T, et al. (1997): Maximum permissible concentrations and negligible concentrations for metals, taking background concentrations into account.

RIVM Report No. 601501001.

Stortelder P.B.M., et al. (1989). Perspectives for water organisms (part 1 and 2) DBW/RIZA Nota No. 89.016a+b, Lelystad, The Netherlands.

Van de Meent, D. et al. (1990): Objective Quality. Background study as a support for the regulatory report on 'Environmental Quality Objectives for Water and Soil, RIVM Report 670101001

Bockting, G.J.M., et al. (1992): Soil-water partition coefficients for some trace metals, national institute of public health and environmental protection, report no. 679101003, Bilthoven, The Netherlands, pp. 51

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.

Other adsorption coefficient indicated as dimensionless:
- log Kp (solids-water in sediment) ,2.94
- log Kp (solids-water in suspended matter) ,3.11
- log Kp (solids-water in soil) ,2.2