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Toxicity to terrestrial plants

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Description of key information

The lowest reported NOEC value for Na2SeO3 is 1.0 mg Se/kg soil for yield of Sorghum vulgare after 6 weeks exposure in a loamy sand soil (Carlson et al., 1991; Klimisch 2).

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:
1 mg/kg soil dw

Additional information

Reliable results are available on toxicity of Na2SeO3 and Na2SeO4 to terrestrial plants. Two studies compare the toxicity of selenite and selenate to yield of Lolium perenne and Sorghum vulgare (Cartes et al., 2005; Carlson et al., 1991). Both studies confirm the higher toxicity of selenate compared to selenite, which is consistent with toxicity data to other terrestrial organisms and the difference in sorption to soil between selenite and selenate. Therefore, only the available reliable results for selenite are taken into account for the hazard assessment of zinc selenite.

Reliable NOEC values for selenite vary between 1 and ≥10 mg Se/kg dw (added concentrations). The lowest reported NOEC value for Na2SeO3 of 1.0 mg Se/kg soil was observed for yield of Sorghum vulgare after 6 weeks exposure in a loamy sand soil (Carlson et al., 1991). Three unbounded NOEC values of ≥4.0 mg Se/kg soil were obtained for the same endpoint and species in 3 other soils differing in pH, organic matter and clay content. Additionally, field data are available for the effect of initial Na2SeO3 applications on yield of maize, carrots, potato and pea in subsequent cropping seasons, with NOEC values of 29, 81, 29 and 7 mg Se/kg dw (Kadar, 1995; Biacs et al., 1995; Kadar et al., 1994; Nyarai-Horvath et al., 1997). These field data confirm the conservative nature of the selected 1 mg Se/kg threshold value for the toxicity of selenite to terrestrial plants.

Reliable chronic toxicity data for Na2SeO4 are available for the monocotyledon plants (Lolium perenne, Triticum aestivum, Sorghum vulgare and Hordeum vulgare) and dicotyledon plants (Medicago sativa, Beta vulgaris and Lycopersicon escultentum) and vary between 0.39 and ≥3 mg Se/kg dw (added concentrations). Two reliable studies (Soltanpour and Workman, 1980 and Wan et al., 1988; both Klimisch 2) reported a total of 14 NOEC values for the effect of Na2SeO4 to Medicago sativa on several endpoints (total plant dry yield, shoot yield and root yield) in 10 different soils. The geometric mean of the lowest NOEC value reported in each study (0.39 and 0.50 mg Se/kg soil, both for root and shoot yield), 0.44 mg Se/kg soil, is the lowest bounded NOEC reported for the toxicity of selenate to terrestrial plants. As mentioned above, this value is not used for the hazard assessment of selenite.

All results are based on nominal added or background corrected measured Se concentrations.