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Toxicity to microorganisms

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Description of key information

The initial test substance concentration of 31.2 mg/L (20.5 mg/L DOC/L) used in the 28- day ready biodegradability study can be considered a presumptive No Observed Effects Concentration (NOEC) since it resulted in ready biodegradability (93% degradation at 28 d but failing the 10-day window) of the test substance in contact with microorganisms from a composite of domestic effluent, river water and soil. 

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
31.2 mg/L

Additional information

The results of a 28 day ready biodegradability test, performed on the test material, 2-Ethyl -1,3-Hexanediol at the Environmental Sciences Section Health and Environment Laboratories of Eastman Kodak Company, Rochester, New York (Watson, 1989) according to the OECD Guideline 301E, EEC/Annex V Guideline C.3 and U.S. EPA/TSCA 40 CFR Section 796.3240 can be used to identify a No Observed Adverse Effect Concentration (NOEC) for microorganisms in water.  The test inoculum used in the study was a mixture of secondary effluent from domestic wastewater from the Van Lare Waste Treatment Plant, water from the Genesee River, and garden soil from Monroe County. The biodegradation of the test material was determined by measurement of the loss of dissolved organic carbon (DOC) from the test chemical solution. The test material in Test flask A was readily biodegradable (93% degradation at d 27) but failed the 10-day window requirement according to the definitions of OECD Guideline 301E. The test material in Test flask B showed evidence of rapid biodegradability in an enhanced biodegradability test (74% degradation at d 42) after inoculation with acclimated test organisms from Test flask A. The initial test substance concentration of 31.2 mg/L (20.5 mg DOC/L) used in the 28-day ready biodegradability study can be considered a presumptive NOEC since it resulted in ready biodegradability (93% degradation at 28 d but failing the 10 day window).

In a supporting study entitled “ Secondary Waste Treatment Compatibility of 2 -Ethyl-1,3-hexanediol: (Watson, 1989), nominal concentrations of the test chemical of 0.1 mg/L, 1 mg/L, 10 mg/L, 100 mg/L and 1,000 mg/L had no significant effect on glucose metabolism in a test with domestic sewage sludge. The study concluded that the test chemical is not expected to affect secondary waste treatment microorganisms adversely at concentrations of less than or equal to 1,000 mg/L. Therefore, the value of 1,000 mg/L is the no observed adverse effect (NOEC) level as determined by the supporting study. However, since ECHA Guidance states that glucose breakdown is not relevant for a sewage biodegradation study, the information from this supporting study is not relied upon for the final NOEC selected.