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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 of wheat glucose syrups having a DE (dextrose equivalent) of at least 20 and for syrups having a glucose content less than 80%.  However, the affect of glucose and maltose on activated sludge has been determined.
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 the present of the test substance. Placak et al. (1947) demonstrated that glucose and maltose are rapidly degraded by activated sludge within 24 hours. As well, the authors demonstrated that there was an increase in the biomass of the activated sludge after 24-hour exposure to 667 ppm of maltose and an increase in the biomass of Sphaerotilus natans (a common activated sludge organism) after 24-hour exposure to 1250 ppm of glucose. The inclusion of the use of glucose in the OECD Modified MITI Test (I) and the ECHA technical guidance on the toxicity to microorganisms implies that glucose does not inhibition the growth, and therefore the respiration, of activated sludge. ...

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