Sodium dithionite

Short-term toxicity to fish

Description of key information

The value of 62.3 mg Na2S2O4/Lfor the fish L. idus is put forward for the environmental classification of sodium dithionite.	

Key value for chemical safety assessment

LC50 for freshwater fish:

62.3 mg/L

Additional information

One reliable acute fish toxicity study that could be used for the hazard and effects assessment of sodium dithionite was identified (BASF, 1982). Tested fish species was the golden orfe Leuciscus idus and the tested compound was sodium dithionite.

  

Compound	MM	%S	LC50 (mg test item/L)	LC50 (mg S/L)	LC50 (mg SO3^2-/L)
Na2S2O4	174.11	36.8	62.3	22.9	57.2

 

Expressed as test ingredient, the nominal 96h-LC₅₀ was 62.3 mg/L. No mortality was noted at a test concentration of 46.4 mg/L, and this for the golden orfe L.idus (test with potassium sulfite). A concentration of 68.1 mg/L resulted in 80% mortality after 96h, and 100% mortality was noted in fish exposed for 1h to 100 mg/L sodium dithionite. Expressed as SO₃^{2 -} or S, the 96h-LC₅₀ was 57.2 or 22.9 mg/L, respectively.

It should be noted that a sulfite-induced oxygen depletion of the test medium upon addition of high concentrations of sodium dithionite was noted. The effect of oxygen consumption was balanced by the continuous aeration of the test solution, therefore the fish were put into the test aquaria immediately after addition of the test substance. As O₂- levels at T=0 were <1.0 mg/L at concentration levels of 68.1 or higher, this oxygen depletion may have caused the rapid mortality (<1h) at these high concentration levels.