Strontium sulphate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

4.4 mg/L

Assessment factor:

10

Marine water

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

8.7 mg/L

Assessment factor:

10

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

5 700 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

no exposure of sediment expected

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

690 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read-across statement:

In the aqueous and terrestrial environment, strontium sulfate dissolves in (pore) water releasing strontium cations and sulfate anions.

Sulfate:Sulfates are of low environmental toxicity (OECD SIDS for Na₂SO₄) as sulfate is essential to all living organisms and their intracellular and extracellular concentrations are actively regulated.

Strontium: No or few ecotoxicological data are available for strontium sulfate itself. For the assessment of the environmental fate and behaviour of strontium substances, a read-across approach is applied based on all information available for inorganic strontium compounds. This is based on the common assumption that after emission of metal compounds into the environment, the moiety of toxicological concern is the potentially bioavailable metal ion (i.e., Sr²⁺).This assumption is considered valid as the ecotoxicity is only affected by the strontium-ion and not by the counter (sulfate) ion.The speciation and chemistry of strontium is rather simple.

 

As reactive electropositive metal, strontium is easily oxidized to the stable and colourless Sr²⁺ion in most of its compounds, the chemical behaviour resembling that of calcium and/or barium (Wennig and Kirsch, 1988). In the environment, the element only occurs in one valence state (Sr²⁺), does not form strong organic or inorganic complexes and is commonly present in solution as Sr²⁺(Lollar, 2005). Consequently, the transport, fate, and toxicity of strontium in the environment are largely controlled by solubility of different Sr-salts (e. g., SrCO₃, Sr(NO₃)₂, SrSO₄, …).

These findings are sufficient justification for the implementation of a read-across strategy with ecotoxicity results obtained in tests that were conducted with different strontium compounds that generate free Sr²⁺-ions in solution, and this for all relevant environmental endpoints that were considered.

In sum, the environmental hazard assessment is based on strontium.

References:Wennig, R.; Kirsch, N. (1988): Chapter 57 Strontium, In: Seiler, U. G. et al.(eds), Handb. Tox. Inorg. Comp. NY, 631-638

PNEC sediment:

The PNEC_sedimentcan be derived from the PNEC_aquaticusing the equilibrium partitioning method (EPM).

A distribution/partition coefficient (K_D) between the water and sediment compartment for strontium has been determined (see chapter 1.3). This resulted in a typical K_{D, susp-water}of 1,291.8 L/kg (logK_D: 3.11). In a first step the units have to be converted from L/kg to m³/m³using the formula below.

K_{D, susp-water}(m³/m³) = 0.9 + [0.1 x (K_{D, susp-water}(L/kg) x 2,500) / 1,000]

This results in a K_{D, susp-matter} of 323.9 m³/m³. This value can be entered in the equation below to calculate the PNEC_sediment:

PNEC_sediment= (K_{D, susp-water}/ RHO_susp) x PNEC_aquaticx 1,000

with the PNEC_aquaticexpressed as mg/L, RHO_susprepresenting the bulk density of wet suspended matter (freshly deposited sediment) (1,150 kg/m³), and a K_{D, susp-water}of 323.9 m³/m³, a PNEC_sedimentthat is expressed as mg/kg wet weight can be derived. This value can be converted to a dry weight-based PNEC, using a conversion factor of 4.6 (CONVsusp = RHOsusp/Fsolid-susp * RHOsolid) kg wet weight/ kg dry weight.

This results in aPNEC_sedimentof 2,720 mg Sr/kg dry sediment corresponding to 5,700 mg SrSO₄/kg dry sediment.

PNEC soil:

The PNEC_soilcan be derived from the PNEC_aquaticusing the equilibrium partitioning method (EPM).

A distribution/partition coefficient (KD) between the water and soil compartment was derived for strontium of 157.03 L/kg (Log KD: 2.2). In a first step the units have to be converted from L/kg to m³/m³using the formula below.

KD,_soil(m³/m³) = 0.2 +[0.6 x (KD,_soil(L/kg) x 2,500) / 1,000]

This results in a KD,_soilof 235.75 m³/m³. This value can be entered in the equation below to calculate the PNEC_soil

PNEC_soil= (KD,_soil/ RHO_soil) x PNEC_aquaticx 1,000

With the PNEC_aquaticexpressed as mg/L, RHO_soilrepresenting the bulk density of wet soil (1,700 kg/m³) and KD,soil is 157.03 m³/m³, a PNEC_soilexpressed as mg/kg wet weight is derived. This value can be converted to a dry weight-based PNEC, using a conversion factor of 1.13 kg wet weight/ kg dry weight.

This results in a PNECs_oilof 329 mg Sr/kg dry soil, re-calculation to strontium sulfate resulted in 689.7 mg SrSO₄/L.

Conclusion on classification

Short-term toxicity EC/LC₅₀values of strontium available for 3 trophic levels are situated between >40.3 mg Sr/L and >125 mg Sr/L, corresponding to > 84.5 mg/L and 262 mg/L strontium sulfate based on an average strontium content of 47.7%. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (a), classification for acute aquatic hazard is not required for strontium sulfate as all EC₅₀/LC₅₀values are above the classification criteria of 1 mg/L.

Long-term toxicity data are available for 3 trophic levels and range from 21 mg Sr/L to ≥ 43.3 mg Sr/L, corresponding to 44 mg/L and 90.8 mg/L strontium sulfate based on an average strontium content of 47.7%. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (b) (i), classification for chronic aquatic hazard is not required for strontium sulfate as all chronic EC₁₀/NOEC values are above the classification criteria of 1 mg/L.