Strontium sulphate

Toxicity to birds

Description of key information

Data from three different studies with chicken (hens) are considered for the derivation of a safe concentration of Sr in food: Weber et al (1971), Doberenz et al (1969) and Shahnazari et al (2006).

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for birds:

12.6 g/kg food

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: Data from three different studies with chicken (hens) are considered for the derivation of a safe concentration of Sr in food: Weber et al (1971), Doberenz et al (1969) and Shahnazari et al (2006):

- Weber et al (1971) found 0% hatchability in eggs that originated from hens given a diet that contained 1.5% or 3.0% Sr (i.e., 15,000 or 30,000 ppm Sr)

- Doberenz et al. (1969) found significant effects on plasma calcium, shell thickness and shell calcium; levels were lowered by dietary levels higher than 1.5% Sr (i.e., 15,000 ppm Sr). Based on this study alone, a NOEC of 15,000 ppm could be proposed; however, as mentioned before Weber et al. (1971) observed 0% hatchability in eggs originating from hens that were fed a diet containing such Sr-concentration. The endpoint “hatchability” was not considered in the study by Doberenz et al (1969).

- Shahnazari et al (2006) fed 13 wk old pullets (egg production at wk 17) for a 43 wk period with three different Sr-treatments (3000, 4500 and 6000 ppm) and found that none of the three treatments adversely affected body weight, feed intake, egg production, egg weight and eggshell quality. The value of 6000 ppm of Sr in food is considered as a relevant NOEC for birds.

Based on this information, the PNECoral for Sr could be derived based on a 47wk-NOEC-value of 6,000 ppm Sr. It is noteworthy that this value is below a value of 6,700 ppm that was reported in a study with young pigs (Bartley and Reber, 1961): a diet based on 0.67% Sr, combined with 0.16%Ca resulted in incoordination and weakness, followed by posterior paralysis. No further information on test duration and Ca-requirement for young pigs in a normal diet is available, and therefore a correct assessment of this data point is currently not feasible.

According to ECHA-Guidance (ECHA, 2008: Chapter R.10 – Dose (concentration)-response regarding environment, and assessment factor of 30 needs to be applied on the lowest chronic NOEC. Hence, an estimated PNECoral for strontium is 6,000 μg/g food / 30 = 200 μg/g dry wt in food. Mora reported internal Sr-concentration levels from insects that originated from areas with elevated Sr-levels in sediment, and these concentrations were situated between 8 and 117 μg/g dry wt, i.e., well below the PNECoral of 200 μg/g dry wt.

It should be noted that, according to the ECHA technical guidance on environmental hazard assessment, ‘if a substance has a bioaccumulation potential and a low degradability, it is necessary to consider whether the substance also has the potential to cause toxic effects if accumulated in higher organisms.’ It further states that the assessment of secondary poisoning takes place as a tiered process, where the first step is to evaluate the bioaccumulative potential of a substance, following the criterion that if BCF ≥ 100 (together with considerations regarding biodegradability). When this criterion is met, the subsequent step to calculate a PNECoral,predator is needed.

As strontium does not meet this requirement, no PNECoral,predator is required for this substance.