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Toxicity to soil microorganisms

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Williams (1984) studied the effect of 1,3 -diphenylguanidine on the growth of soil micro-organisms. The compound was spread on a polycarbonate membrane or imbedded on aluminiun foil in an epoxy resin (Araldit), and was thus in indirect (via membrane pores) or direct contact with a not further specified soil (moistened John Innes N°.1 soil). No colonies formed during the 3 -month experiment.

The compound was also placed in nutrient agar, inoculated with an aquaeous soil extract (3.0E07 individuals/ml) and incubated for 4 and 14 days at 25°C. The LD50 for both incubation times was given as > or = 0.1%, based on the growth rate of control experiments. This concentration was characterized by the author as highly toxic, although when converted it corresponds to an amount of < or = 1 g/l. The author pointed out that experiments of this type are not suitable for evaluating the microbial degradation of rubber (and thus the microbial toxicity of the rubber chemicals added) as they do not consider the chemical change of the test compound during vulcanization.

According to claimed uses of 1,3 -diphenylguanidine soil exposure is likely. At the moment no relevant data is available for characterizing its effects on micro-organisms inhabiting soils. As the risk assessment demonstrates that there is no risk for those organisms using the PNEC derived through equilibrium partitioning method, no test is needed for covering this question.