Registration Dossier

Ecotoxicological information

Long-term toxicity to fish

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

A value of ≥436.5 mg Na2S2O4/L was initially derived, but as oxygen depletion upon administration of this test substance has not been taken into account, a more realistic chronic value of 46.4 mg Na2S2O4/L is put forward for the environmental classification and effects assessment of sodium dithionite.	

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater fish:
46.4 mg/L

Additional information

No reliable data on chronic toxicity of sodium dithionite towards fish were identified. Reliable chronic toxicity data, however, were reported in a GLP-OECD Guideline 210 early-life stage (ELS) study, using sodium sulfite (Na2SO3) as test substance. As dithionite rapidly decomposes into sulfite and sulfate under aerobic environmental conditions, these data are useful for assessing chronic toxicity of dithionite.

In this study, five different substance concentrations were evaluated, but no adverse effects on hatching, post–hatch mortality, health, length and dry weight of surviving fish were observed. Consequently, a chronic nominal 34d-NOEC of ≥316 mg test substance for fish (i.e., ≥200.5 mg SO32- or ≥80.4 mg S/L) is proposed for this endpoint.

Taking into account that dithionite decomposes into sulfite and sulfate/thiosulfate at a 50/50 rate of S-atoms, this value can be translated into ≥436.5 mg Na2S2O4/L.

 

It should be noted, however, that the calculated NOEC for fish is markedly higher than the acute value of 62.3 mg/L for this trophic level. This is due to the fact that oxygen depletion caused acute toxicity, whereas the test design of the ELS test (aerated test media, using sodium sulfite as test compound) prevents mortality of exposed fish due to oxygen depletion. A more realistic long-term NOEC is therefore the highest acute exposure concentration that resulted in 0% mortality. This value of 46.4 mg Na2S2O4/L is put forward for the environmental classification and effects assessment of sodium dithionite.