Zinc selenite

Toxicity to aquatic algae and cyanobacteria

Description of key information

Reliable NOEC and EC50 values for freshwater algae and cyanobacteria range from 197 to 4570 and from 355 to 44240 µg Se/L, respectively. The most critical NOEC and EC50 were 197 and 355 µg/L, respectively, and represent effect concentrations for maximal cell density of the unicellular green alga Chlamydomonas reinhardtii from a 96-h study with selenate. However, an EC50 for cell density was not considered relevant for acute toxicity and a critical EC50 of 44240 µg Se/L was selected based on a 72-h growth-rate inhibition study with sodium selenite and the unicellular green alga Selenastrum capricornutum according the OECD 210 guideline. The NOEC and EC50 for saltwater algae were 11000 and 45000 µg/L, respectively, and represent growth-rate based effect concentrations from a 96-h study on the toxicity of selenate to the halophilic Dunaliella viridis. All reliable chronic NOEC values were used for the derivation of a PNECwater based on the statistical extrapolation approach.

Key value for chemical safety assessment

EC50 for freshwater algae:

44 240 µg/L

EC50 for marine water algae:

45 000 µg/L

EC10 or NOEC for freshwater algae:

197 µg/L

EC10 or NOEC for marine water algae:

11 000 µg/L

Additional information

Overall, 44 studies were identified for growth inhibition to algae; 37 studies were considered relevant (including 3 review publications); only 4 studies were considered reliable (Klimisch 2). Reliable data were available for Na₂SeO₃ and Na₂SeO₄ and both for freshwater and saltwater algae. The freshwater algae represented were the unicellular green algae Selenastrum capricornutum and Chlamydomonas reinhardtii. The halophilic Dunaliella viridis was considered representative for saltwater algae. Additionally, there were 13 studies identified reporting relevant information for cyanobacteria. Only one study was considered reliable. This study reported 10-d NOEC values for the blue-green alga Anabaena flos-aquae obtained from experiments with Na₂SeO₃, Na₂SeO₄ and seleno-L-methionine (Kiffney and Knight, 1990). The NOEC values from these experiments were based on chlorophyll a content and were reported to be 1030, 995 and 30.5 µg Se/L, respectively. 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. All results are based on added dissolved Se concentrations.

NOEC and EC50 values for freshwater algae ranged from 197 to 4570 and from 355 to 44240 µg Se/L, respectively. The lowest NOEC and EC50 are growth based effect concentrations for maximal cell density of the unicellular green alga Chlamydomonas reinhardtii from a 96-h study with selenate (Geoffroy et al., 2007). The highest NOEC and EC50 wer reported for a standard OECD 201-conform 72-h growth-rate inhibition study with sodium selenite and the unicellular green alga Selenastrum capricornutum (LISEC, 1992). Brix et al. (2004) reported the only available reliable data for a saltwater species (the halophilic alga Dunaliella viridis). The growth rate-based 96-h NOEC and EC50 for Se as selenate were reported to be 11000 and 45000 µg Se/L, respectively. Selenium toxicity appears to be highly species and endpoint-specific. Based on the data available, no conclusions could be made on the relative toxicity of selenite and selenate.