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Ecotoxicological information

Toxicity to terrestrial plants

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Reliable toxicity data for terrestrial plants could not be identified for barium, sulfide or sulfate.

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Toxic effects of released sulfide from BaS are not relevant for the hazard assessment of BaS in soils as sulfide is oxidized to sulfate, and thus the toxicity of sulfate should be assessed. Sulfate is essential to all living organisms, their intracellular and extracellular concentrations are actively regulated and thus, sulfates are of low toxicity to the environment, including soils. As essential nutrient, sulfate is of low toxicity particularly to plants (OECD SIDS for Na2SO4). Further, the solubility product constant of barium sulfate of 1.1×10–10 indicates that once sulfide released from BaS is oxidized to sulfate, barite (BaSO4) precipitates and is rendered less bioavailable and less toxic. Thus, the barium cation is the moiety of toxicological concern (if any), and the soil hazard assessment is based on barium.

According to CICAD 33 (WHO, 2001), there is no indication that barium is toxic to terrestrial plants. Environment Canada (1996) performed toxicological tests with very soluble BaCl2*H2O on radish (Raphanus sativa) and lettuce (Lactuca sativa) in artificial soil. The NOEC and EC50 for seedling emergence of lettuce amount to 177 and 868 mg/kg and for radish to 1055 mg/kg and 2944 mg/kg, respectively. Even though, the reported toxic endpoints are likely due to chloride rather than barium, the most sensitive endpoint for lettuce corresponds to a NOEC of 218 mg BaS/kg and indicates that plants are presumbably not overly more sensistive than invertebrates (lowest EC10 for reproduction of springtails (Folsomia candida) amounts to 260 mg BaS/kg). Considering that (i) barium chloride, a very soluble barium substance was applied in (ii) an artificial soil with a presumbably high bioavailability of chloride and barium, as well as (iii) roots are commonly known to be very sensitive to chloride, plants in natural soils are not expected to be more sensitive to BaS than invertebrates