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Toxicity to microorganisms

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Description of key information

The NOEC of 20 mg carbon/L (i.e., 26.25 mg 3-methylpyridine/L, or 0.282 mmol/L) from the guideline ready biodegradability assay by Weytjens and Wils (1991) was the key value for the short-term toxicity to micro-organisms in sewage treatment plants for the chemical category (pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine).  

Key value for chemical safety assessment

EC50 for microorganisms:
20 mg/L

Additional information

The point of departure for the derivation of the PNECSTPwas the NOEC from the ready biodegradability CO2 evolution assay (OECD Guideline 301B) of 20 mg C/L (i.e., 26.25 mg 3 -methylpyridine/L, or 0.282 mmol/L), for the chemical category including pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. 

2-Methylpyridine (alpha-picoline, CAS 109-06-8) is a member of a category with is utilized for “read-across” to fill data gaps and for risk assessment for hazard identification. The category of pyridine and alkyl pyridine derivatives is comprised of pyridine (CAS 110 -86 -1), 2-methylpyridine (CAS 109-06-8), 3-methylpyridine (CAS 108-99-6) and 4-methylpyridine (CAS 108-89-4). The foundation of the category is a common functional group (the pyridine unsaturated ring structure) and similar physico-chemical properties, environmental fate and toxicity, and mammalian toxicity. Similar ecotoxicological and environmental fate properties derive from physico-chemical parameters and common pathways of metabolism and elimination among all members of the category. Three of four members of this category have harmonized classification and labelling. Read-across for non-harmonized endpoints is adequate for risk assessment purposes.