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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

Two reliable studies were considered for the evaluation of sulfite/disulfite toxicity towards aquatic algae. Stamm (1980) reported on the effects of potassium sulfide (K2SO3) on the growth rate of different algal species (Scenedesmus brasiliensis, Chlorella vulgaris, Chlamydomonas reinhardtii). Growth stimulation was sometimes observed at lower test concentrations, but only inhibition was considered for effects asssessment purposes.

Reported 96h-EC50 values were situated between 0.5 and 1 mM (values estimated from a graph), which are converted to 63-126 mg test item/L or 40.0-79.9 mg SO32-/L. The reported NOEC-value was 37.8 mg test item/L, which is equivalent to 24.0 mg SO32-/L.

BASF (1989) investigated the effects in sodium metabisulfite (Na2S2O5) on the growth rate of the green algaScenedesmus subspicatus. A 96h-study was conducted, and the derived effects levels after a 72h-exposure period were considered for assessment purposes. The EC50 and EC10 values were 43.8 and 33.3 mg test item /L, wich corresponds to 36.8 and 28.0 mg SO32-/L, respectively (or 14.8 and 11.2 mg S/L, respectively).

 

The data reported in the BASF (1989) study were taken forward in the hazard and effects assessment of sulfites/disulfites:

-      Scenedesmus subspicatus was more sensitive than the three species that were used by Stamm (1980);

-      effects levels reported by Stamm (1980) were graphic estimates;

-      reported study by BASF (1989) was conducted according t oOECD Guideline No. 201

 

Data on sulfite-induced inhibition of photosynthesis were also reported in open literature (e.g., Wodzinski et al, 1977; Sheridan, 1978). This endpoint, however, is considered less ecological relevant compared to growth rate. Data were therefore not further evaluated.

 

The values of 36.8 and 28.0 mg SO32-/L (72h-EC50 and 72h-EC10, respectively) were put forward for the environmental classification and effects assessment of sulfite/disulfite compounds.