Sodium selenite

Endpoint summary

Additional information

Added risk approach

Selenium is naturally present in all environmental compartments. The median baseline background concentration in unpolluted stream water in Europe is 0.32 µg Se/L (Vercaigne et al., 2010). These background concentrations are significant compared to the PNEC freshwater (2.67 µg Se/L). Moreover, toxicity due to dietary exposure to Se is more critical compared to direct exposure to dissolved Se, with a critical Se concentration in water for secondary poisoning of 0.21 µg Se/L (based on PNECoral of 1 mg Se/kg diet and a generic bioaccumulation factor of 4721 L/kg). Therefore, the added risk approach is employed and all NOEC and EC10 values are based on added selenium concentrations, without taking into account the natural background concentration in water. In essence this added risk assessment approach assumes that species are fully adapted to the natural background concentration and therefore that only the anthropogenic added fraction should be regulated or controlled (Appendix R.7.13-2 of the REACH guidance on “Environmental risk assessment for metals and metal compounds”). Because measured background concentrations in exposure media are generally below the detection limit (generally 1-2 µg Se/L) and chronic NOEC values vary between 10 and 11000 µg Se/L, these NOEC values can be considered as added dissolved Se concentrations.

Summary toxicity data

Reliable ecotoxicity results selected for the effect of selenium on aquatic organisms are available for H₂SeO₃, Na₂SeO₃, SeO₂ Na₂SeO₄ and seleno-(D)L-methionine. All data were reported based on dissolved elemental Se concentrations. The data for Se-(D)L-methionine were not taken into account for the assessment of direct effects of selenite to aquatic organisms because there is some concern on different biochemical behaviour of this selenium containing amino acid compared to inorganic Se compounds. The data available for the inorganic Se compounds do not allow conclusions on the effect of water properties (pH, hardness, etc.) or Se substance on toxicity of selenium to aquatic organisms. Therefore, all reliable toxicity data for all inorganic Se substances, expressed on a dissolved selenium basis, were grouped for the effects assessment.

The table below presents an overview of the lowest reliable toxicity data for the various trophic levels of aquatic organisms.

Trophic level	Substance	Species	Parameter	Endpoint	Value (µg Se/L)	Reference
Acute toxicity, freshwater
Fish	SeO2	Pimephales promelas	mortality	96-h LC50	2060	Cardwell et al., 1976
Invertebrates	Na2SeO3	Daphnia magna	mortality	48-h LC50	550	Maier et al., 1993
Algae	Na2SeO3	Selenastrum capricornutum	growth rate	72-h EC50	44240	LISEC, 1992
Acute toxicity, marine water
Fish	Na2SeO3	Morone saxatilis	mortality	96-h LC50	3300	Chapman, 1992
Algae	Na2SeO4	Dunaliella viridis	growth rate	96-h EC50	45000	Brix et al., 2004
Chronic toxicity, freshwater
Fish	Na2SeO3	Lepomis macrochirus	prespawning mortality	258-d NOEC	10	Hermanutz et al., 1992
Invertebrates	H2SeO3	Daphnia magna	reproduction	28-d NOEC	70	Kimball, 1978
Algae	Na2SeO4	Chlamydomonas reinhardtii	growth	96-h NOEC	197	Geoffroy et al., 2007
Plants	Na2SeO3	Lemna minor	growth (%surface coverage)	14-d NOEC	80	Jenner and Janssen-Mommen, 1993
Chronic toxicity, marine water
Fish	Na2SeO3	Pagrus major	growth	28-d NOEC	25	Kim and Kang, 2014
Invertebrates	Na2SeO3	Allorchestes compressa	reproduction	28 -d NOEC	44	Ahsanullah and Brand, 1985
Algae	Na2SeO4	Dunaliella viridis	growth rate	72 -h NOEC	11000	Brix et al., 2004

Reliable short-term toxicity data for freshwater organisms are available for three trophic levels: aquatic invertebrates, fish and algae. Acute L(E)C50 values vary between 550 and 48200 µg Se/L, with the lowest acute effect value was a 48-h LC50 of for the effect of Na₂SeO₃ on mortality of Daphnia magna. Acute toxicity data are also available for marine fish and algae (3300-76000 µg Se/L).

Reliable long-term toxicity data are available for 11 freshwater organisms covering the three trophic levels. The lowest chronic NOEC, 10 µg Se/L, was observed for the effect of Na₂SeO₃ on pre-spawning mortality of Lepomis macrochirus after 238 days exposure. Reliable long-term toxicity data were also identified for the effect of Na₂SeO₃ and Na₂SeO₄ on a marine fish, a marine alga and two marine invertebrates with NOEC values between 25 and 11000 µg Se/L.

Data for dietary toxicity are also available for 6 freshwater fish species with NOECoral values between 2.2 and 89.8 mg/kg dw diet for growth and mortality based on studies with Na₂SeO₃, SeO₂, Na₂SeO₄ and seleno-(D)L-methionine. Because after release in the environment, inorganic Se can be transformed into Se containing amino acids, data for seleno-methionine and seleno-cysteine are included for the assessment of secondary poisoning (through PNECoral and bioconcentration factors).