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Ecotoxicological information

Long-term toxicity to fish

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Description of key information

, a chronic nominal 34d-NOEC  of ≥316 mg test substance for fish, i.e., ≥80.4 mg S/L is proposed for this endpoint. Translating this value to thiosulftate results in ≥140.6 mg S2032-/L.

Key value for chemical safety assessment

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

Additional information

No reliable data on chronic toxicity of ammonium thiosulfate to 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. The following arguments are put forward that support a read-across approach of data generated with sulfites/disulfites:

  •  thiosulfates oxidize to sulfites (and subsequently to sulfate) under normal environmental conditions (e.g., through microbial activity);
  •  the acute toxicity of thiosulfates and sulfites/disulfites are both related to their impact on physicochemical parameters (decrease on the pH through formation of H2SO4, oxygen depletion due to oxidation of these reducing sulfur substances);
  •  acute fish toxicity data for sulfites/disulfites were lower than those that were identified for thiosulfates. The key acute value for sulfites was 149.6 mg SO32-/L, whereas the lowest value using a thiosultate as test substance was 831 mg/L as SO32-.Both data were generated for the same test species (Salmo gairdneri). Similar findings were observed for other trophic levels. It is therefore concluded that read-across from chronic sulfite toxicity data can be considered as a worst-case.

 

 

In the ELS study with sodium sulfite, 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., ≥80.4 mg S/L is proposed for this endpoint. Translating this value to thiosulftate results in ≥140.6 mg S2032-/L.