Strontium sulphate

Endpoint summary

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

Summary:

Short-term toxicity data

Reliable acute data are available for three trophic levels: algae, invertebrates and fish.

(i)            An unbounded value of > 90.8 mg SrSO₄/L (>43.3 mg Sr/L) was identified for algae.

(ii)           The only bounded acute value of 262 mg/SrSO₄/L (125 mg Sr/L) is available for the invertebrateDaphnia magna.

(iii)          The lowest acute effect value (based on measured Sr in the test medium) was an unbounded value of >40.3 mg Sr/L (>84.5 mg SrSO₄/L) for the fishCyprinus carpio.

 

It should be noted that the actual E(L)C₅₀values for fish and algae may be well above the reported values as not even partial effects (i.e., mortality or growth rate inhibition) were noted at the highest test concentrations. The table below provides an overview of the most sensitive, reliable, short-term toxicity freshwater data available for strontium.

 

Table: Most sensitive reliable short-term toxicity endpoints for strontium in freshwater

Species	Parameter	Endpoint	Value (mg Sr/L)	Value (mg SrSO4/L)	Reference
Acute fish data
Cyprinus carpio	mortality	96h-LC50	> 40.3	> 84.5	Tobor-Kaplon (2010)
Acute invertebrate data
Daphnia magna	mortality/immobility	48h-LC50	125	262	Biesinger and Christensen (1972)
Algal data
Pseudokirchneriella subcapitata	growth rate	72h-ErC50	> 43.3	> 90.8	Tobor-Kaplon (2010)

 

Long-term toxicity data

Reliable studies on chronic toxicity of strontium to the aquatic environment are available for three trophic levels: algae, invertebrates and fish. The toxicity tests were performed using strontium nitrate or strontium chloride hexahydrate as test substance.

 

(i)            In the study of growth inhibition of the algae speciesPseudokirchneriella subcapitataby Tablor - Kaplon,all significant effect levels (acute and chronic) were equal or higher than 43.3 mg Sr/L (conservative value). Thus, the 72-h NOEC is ≥ 90.8 mg SrSO₄/L.

(ii)           The study on the chronic toxicity of strontium to invertebrates (Biesinger and Christensen, 1972) reported a calculated NOEC forDaphnia magna(i.e., EC₁₆/2) of 21 mg Sr/L (44 mg SrSO₄/L.

(iii)          A chronic fish study according to OECD 210 (Egeler and Morlock, 2013) was performed withDanio rerio. The NOEC (nominal) was set to ≥100 mg/L for strontium nitrate, corresponding to a re-calculated NOEC (nominal) for strontium sulfate of ≥ 86.8 mg/L.

 

The PNEC_aquaticcalculation will be conducted using the assessment factors method since a large dataset from long-term tests for different taxonomic groups is not available, a Species Sensitivity Distribution (SSD) cannot be developed and statistical extrapolation methods can thus not be used to derive the PNEC_aquatic. An overview of available long-term data used for PNEC-derivation is provided in the Table below.

 

Table: Most sensitive reliable long-term toxicity data for strontium in freshwater

 

Species	Parameter	Endpoint	Value (mg Sr/L)	Value (mg SrSO4/L)	Reference
Chronic fish data
Danio rerio	mortality	34d-NOEC	≥ 41.4	> 86.8	Egeler and Morlock (2013)
Chronic invertebrate data
Daphnia magna	mortality	21d-NOEC	21	44	Biesinger and Christensen (1972)
Chronic algae data
Pseudokirchneriella subcapitata	growth rate	72h-NOECr	≥ 43.3	> 90.8	Tobor-Kaplon (2010)