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Toxicity to microorganisms

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The aim of the assessment of toxicity to sewage treatment plant microorganisms is the protection of the biodegradation and nutrient removal functions, and process performance in general, of municipal and industrial sewage treatment plants (ECHA, 2008).  There was no information available concerning the toxicity to microorganisms for the notifiable substance.  However, metabolic data demonstrate that the notifiable substance, as well as the read-across substances (maltose, maltitol, sorbitol, wheat glucose syrup (WGS), and dextrin) share a common metabolic pathway as they are converted to D-glucose and/or sorbitol via hydrolysis of their glycosidic linkages by the intestinal brush border carbohydrases. On the basis of their common mono- and disaccharide metabolites, the properties of the notifiable substance is expected to be similar to the read-across substances maltose, sorbitol, maltitol, WGS and dextrin.  Considering this, it is anticipated that exposure to any of the aforementioned saccharides would ultimately result in the formation of D-glucose and/or sorbitol.  As such, maltose, sorbitol, maltitol, WGS, and dextrin may be used as appropriate surrogates, considering their common metabolic products.
Activated sludge from sewage treatment plants can utilize glucose and maltose as sources of food material as demonstrated in the OECD methodology for ready biodegradability (OECD, 1992), ECHA technical guidance on the toxicity to microorganisms (ECHA, 2008) and the studies conducted by Placak et al. (1947). The Modified MITI Test (I) for determination of ready biodegradability indicates that 0.1% of glucose is to be included in the medium used to maintain the activated sludge prior to analysis. The technical guidance document indicates that the content of a ready or inherent biodegradability test can be used to derive a NOEC when a toxicity control has been included that shows good degradation of a positive control substance (e.g. glucose, sodium acetate) in t...

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