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Toxicity to microorganisms

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Description of key information

In an oxygen consumption test following OECD guideline 209, with unadapted activated sludge from a laboratory plant as inoculums, an EC50 -3 hours of 147 mg/l was estimated (79 -208 mg/l).

Key value for chemical safety assessment

EC50 for microorganisms:
147 mg/L

Additional information

Tomlinson et al. (1966) investigated the effect of 1,3-diphenylguanidine on the nitrification process in municipal waste waters. They incubated purified activated sludge (dw = 1350 - 1700 mg/l) for 2 - 4 hours in residential waste water that was free of suspended particles in a shake culture (25°C; pH= 7.6 - 7.8) at various test compound concentrations. The nitrification rate was determined quantitatively by colorimetric measurement of the NO2- and NO3- concentrations. The effective concentration for decreasing the nitrification rate by 75% in the first stage (NH4 + =>NO2 -) compared to the control was estimated at 50 mg/l (highest tested ineffective concentration).

In vitro studies on cell homogenates of Escherichia coli B showed an inhibitive effect of 1,3 -diphenyl guanidine on specific steps of protein biosynthesis, due to non competitive inhibition of the phenylalanyl-tRNA synthetase. 50% inhibition occured at a molar inhibitor/amino acid ratio of 3.2. At an L-phenylalanine concentration of 0.3 mmol/l (49.5 mg/l) this corresponds to an EC50 of 202.8 mg/l 1,3 -diphenylguanidine/l.

Lastly, in the oxygen consumption test following OECD guideline 209, with unadapted activated sludge from a laboratory plant as inoculums, an EC50 -3 hours of 147 mg/l was estimated (79 -208 mg/l).