Strontium

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Results are based on nominal values, and test did not exacty follow existing guidance (1972-study), but followed test method well described and test conditions (eg.g. test medium composition) were properly identified.

Justification for type of information:

Strontium metal is highly reactive and instantly oxidizes upon contact with water. It decomposes completely. During the redox-reaction with water, a strong evolution of hydrogen gas and an immediate precipitation of a white, crystalline solid (i.e. Sr(OH)2) is observed (Sr2+ + 2OH- + H2 (g). The amount of dissolved Sr cations is determined by the solubility of the Sr(OH)2 precipitate. According to OECD guideline 105 (1995) and EU method A.6 (2006), the water solubility of strontium was determined to be 6.74 ± 0.14 g/L under the conditions of the test (flask method under protective gas atmosphere; loading of 41 g Sr/L, at 20.0 ± 1.0 °C, pH >13).
Due to the buffering capacity of most environmental systems, it may reasonable be assumed that the formed hydroxide ions are neutralised in the environment by different processes including precipitation.

The solubility of strontium is not greatly affected by the presence of most inorganic anions as there is little tendency for strontium to form complexes with inorganic ligands (Krupka et al. 1999. EPA 402-R-99-004B and references therein). Free Sr2+ cations are mobile under most environmental conditions, despite the relatively low solubility of strontium carbonate and strontium sulfate at neutral to high pHs. In solutions with a pH below 4.5, the Sr2+ ion is dominant. Under more neutral conditions (pH 5 to 7.5), SrSO4 forms. Strontium carbonate controls strontium concentrations in solutions only under highly alkaline conditions. Further, dissolved strontium forms only weak aqueous complexes with chloride and nitrate (Salminen et al. 2015 and references therein, Krupka et al. 1999. EPA 402-R-99-004B). Regarding monodentate and bidentate binding to negatively-charged oxygen donor atoms, including natural organic matter, alkaline earth metals, such as strontium, tend to form complexes with ionic character as a result of their low electronegativity. Ionic bonding is usually described as resulting from electrostatic attractive forces between opposite charges, which increase with decreasing separation distance between ions (Carbonaro and Di Toro. 2007. Geochim Cosmochim Acta 71 3958–3968; Carbonaro et al. 2011. Geochim Cosmochim Acta 75: 2499-2511 and references therein). Thus, strontium does not form strong complexes with fulvic or humic acids based on the assumption that strontium would exhibit a similar (low) stability with organic ligands as calcium and that strontium could not effectively compete with calcium for exchange sites because calcium would be present at much greater concentrations (Krupka et al. 1999. EPA 402-R-99-004B). In sum, strontium ions are highly mobile, occur only in one valence state (2+), i.e. are not oxidized or reduced, and do not form strong complexes with most inorganic and organic ligands (Krupka et al. 1999. EPA 402-R-99-004B; Salminen et al. 2015). Thus, it may further be assumed that the behaviour of the dissociated strontium ions in the environment determine the fate of strontium upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning as well as the distribution in environmental compartments (water, air, sediment and soil) and subsequently the ecotoxicological potential.Therefore, the assessment of the ecotoxicity of strontium is based on elemental strontium concentrations. Read-across of ecotoxicity data available for soluble strontium substances is applied since the strontium ions determine the ecotoxicological potential of strontium.

Qualifier:

no guideline available

Principles of method if other than guideline:

Not a guideline study but meets generally accepted scientific standards and methodology is well documented and described

GLP compliance:

not specified

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM- Common name: Daphnia magna- Strain: laboratory clone - Source: University of Michigan- Age at study initiation (mean and range, SD): 12h +/- 12h- Feeding during test: no

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

45.2 mg/L as CaCO3

Test temperature:

18 +/- 1 °C

pH:

7.74

Dissolved oxygen:

+/- 9 mg O2/L

Salinity:

not reported

Nominal and measured concentrations:

nominal/measured test concentrations not reported: geometric series of 5-12 concentrations (not specified for Sr)

Details on test conditions:

- No. of organisms per vessel: 10- No. of vessels per concentration (replicates):2- No. of vessels per control (replicates): not reportedTEST MEDIUM / WATER PARAMETERS- Source/preparation of dilution water: Lake Superior water; unfiltered water strained through a #20 bolting cloth- Metals: 14 µg Ba/L ; 16 µg Sr/L ; 0.78 µg Zn/L ; <0.5 µg Ni/L ; 1.51 µg Cu/L ; <0.5 µg Co/L ; < 0.01 g Hg/L ; < 0.1 µg Cd/L - Chloride: 1.22 mg/L- Alkalinity: 42.3 mg/L as CaCO3- Ca: 13.7 mg /L- Mg: 3.12 mg/L- K: 0.53 mg/L- Na: 1.13 mg/LEFFECT PARAMETERS MEASURED (with observation intervals if applicable) : complete immobilisation or death

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

LC50

Effect conc.:

125 000 µg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

metal ion -based

Basis for effect:

mortality

Remarks:

including immobility

Remarks on result:

other: not reported

Reported statistics and error estimates:

Results were statistically evaluated with the method of Litchfield and Wilcoxon (1949). LC50 was used for survival and represents an interpolation from three or more partial-effect concentrations.

Chemical characteristics of Lake Superior water were monitored during the testing period according to procedures outlined by the American Public Health Association and procedures employing atomic absorption spectroscopy.

Validity criteria fulfilled:

no

Conclusions:

Results are based on nominal values, and test did not exacty follow existing guidance (1972-study), but followed test method well described and test conditions (eg.,. test medium composition) were properly identified.The resulting 48h-EC50 of 125,000 ug Sr/L is (endpoint= immobility) is an acceptable value for this endpoint, and can be used for classification purposes.

Description of key information

A reliable, nominal 48h-EC50 of 125 mg Sr/L has been reported by Biesinger and Christensen (1972) for the cladoceran  Daphnia magna as test organism.   

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

125 mg/L

Additional information

The reported 48h-EC₅₀ of 125 mg Sr/L by Biesinger and Christensen (1972) for Daphnia magna is based on nominal test concentrations, using the soluble SrCl₂ as test substance. The followed test procedure in this 1972 -study was well described and test conditions (eg.g. test medium composition) were properly identified.

No reliable data were identified for the marine compartment.