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Toxicity to microorganisms

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Description of key information

Based on a respiration inhibition study with nitrifying bacteria, the 3-hour NOEC for diethylene triamine was determined to be 6 mg/L, while the 3 –hour EC50 for diethylene triamine was determined to be 32.7 mg/L. 

Key value for chemical safety assessment

EC50 for microorganisms:
32.7 mg/L
EC10 or NOEC for microorganisms:
6 mg/L

Additional information

A total of eight microorganism studies were listed for diethylene triamine. Of these eight studies, five studies were assigned Klimisch scores of 4 based on the unavailability of the original study for detailed review. Three remaining studies were examined and assigned Klimisch scores of 2 indicating that these studies were deemed reliable and useful for risk assessment. One study examined growth inhibition of the bacteria, Pseudomonas putida,over a 17-hour exposure period and reported a 17-hour EC10 and EC50 of 0.4 mg/L and 1.7 mg/L diethylene triamine, respectively. Another study examined inhibition of respiration of nitrifying bacteria over a 3-hour exposure period and reported a 3-hour NOEC and EC50 of 6 mg/L and 32.7 mg/L diethylene triamine, respectively. Another study examined activated sludge respiration inhibition over a 30 minute exposure period and reported a 30-min EC20 and EC50 of 80 mg/L and 2,000 mg/L diethylene triamine, respectively. According to REACh guidance (R.7.8.17.1) microorganism toxicity tests with P. putidaare not preferred for developing a PNEC STP, thus the toxicity results from this type of study was not preferentially selected as the key parameter for this endpoint. Both the inhibition of nitrifying bacteria and the activated sludge inhibition test are preferred tests for developing a PNEC STP according to REACh guidance (R.7.8.17.1). In this case, the NOEC value of 6 mg/L based on inhibition of respiration of nitrifying bacteria was selected as the key parameter for this endpoint, since this was the lowest toxicity value reported for microorganisms which also resulted in the lowest, most conservative PNEC STP value.

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