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Toxicity to microorganisms

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Description of key information

The value of 82.4 mg (SO3)2-/L  is put forward for the environmental assessment of sulfite/disulfite compounds to micro-organisms.	

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
82.4 mg/L

Additional information

Reliable acute toxicity data are available from GLP-conform guideline studies for microorganism (activated sludge) exposed to sodium sulfite, ammonium thiosulfate and sodium dithionite. Respective EC/LC50 values are well above respective test limits of 100 mg/L, i.e. 3-h EC50 for activated sludge ranging from 187.6 mg sodium dithionite/L to > 1000 mg sodium sulfite or ammonium thiosulfate/L (corresponding to 172.2 mg/L to 1079 mg/L in terms of SO32—equivalents).

Reliable GLP-conform chronic toxicity data for microorganisms are available for all three regarded salts. Respective EC10 values for respiration inhibition of activated sludge ranging from 89.8 mg sodium dithionite/L to >1000 mg ammonium thiosulfate/L, which corresponds to 82.4 mg SO32—/L to 1079 mg SO32—/L, respectively.

Supporting information indicate as slightly lower effect level in Pseudomonas putida with respective 17-h EC10 ranging from 23 mg SO32—/L to 77.3 mg SO32—/L. However, as respiration tests with activated sludge is a more relevant test design for evaluating effects of a substance on micro-organisms, and taking into account that the studies were OECD Guideline GLP-study, the data reported in the activated sludge studies are put forward for the effects assessment for micro-organisms.

Therefore, a low potential for acute/chronic toxicity to microorganisms is considered.