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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The values of 36.8 and 28.0 mg (SO3)2-/L (72h-EC50  and 72h-EC10, respectively) were put forward for the environmental classification and effects assessment of sulfite/disulfite compounds.	

Key value for chemical safety assessment

EC50 for freshwater algae:
36.8 mg/L
EC10 or NOEC for freshwater algae:
28 mg/L

Additional information

For sulfite, thiosulfate and dithionite reliable acute toxicity data are available for freshwater algae. The 72-h EC50 ranging from 43.8 mg disodium disulfite/L to 206.2 mg sodium dithionite/L, which corresponds to 36.8 mg/L to 189 mg/L sulfite equivalents, respectively. Thiosulfate as well as dithionite are well above 100 mg/L in terms of sulfite equivalents.

Thus, it appear that sulfite has a higher potential for acute toxicity to freshwater algae than thiosulfate and dithionite compounds.

Reliable chronic toxicity data for freshwater algae are available for sulfite, thiosulfate and dithionite compounds. Respective 72-h NOEC/EC10 as measured by inhibition of growth rate of Desmodesmus subspicatus (disodium disulfite, sodium dithionite) or Pseudokirchnerella subcapitata (ammonium thiosulfate) are well above 10 mg/L in terms of test item as well as sulfite equivalents, i.e. for disodium disulfite 72-h EC10: 33.2 mg/L (corresponding to 28 mg SO32—equivalents /L); for sodium dithionite 72-h NOEC: 81.7 mg/L (corresponding to 75 mg/L SO32—equivalents); for ammonium thiosulfate no toxicity up to the highest tested concentration of 100 mg test item/L was observed.

Therefore, sulfite compounds as well as thiosulfate and dithionite compounds appear to have a low potential for chronic toxicity to freshwater algae.