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Ecotoxicological information

Toxicity to soil microorganisms

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L-tryptophan significantly induced the respiration rate in the arable soil as well as in the forest soil. The mean SIR (substrate-induced respiration) of three replicates was 45.5 nmol CO2 per g soil per hour (SD 7.19 nmol CO2 per g soil per hour) for arable soil and 42.4 nmol CO2 per g soil per hour (SD 1.53 nmol CO2 per g soil per hour) for forest soil. This indicates that L-tryptophan is metabolised and used for primary metabolism (via the kynurenine pathway) and it is very unlikly that the substance possess any advers effect for soil microorganisms.

This is further supported by a study, in which the growth and yield of mung bean in the presence of Rhizobium phaseoli was investigated. The presence of L-tryptophan at a concentration of 0.2 g/L did not alter the growth and yield promoting activity of the soil microorganisms (NOEC>=0.2 g/L; see section 6.3.3 endpoint study record Zahir et al_2010 ). Based on these findings a low toxicity of L-tryptophan to soil microorganisms is to be expected. Moreover, L-tryptophan is considered as a important precursor of plant growth regulator. Therefore, the performance of further studies is assumed to be not justifiable.