Registration Dossier

Data platform availability banner - registered substances factsheets

Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
Absorption rate - dermal (%):
Absorption rate - inhalation (%):

Additional information

L-tryptophan is an essential amino acid, which cannot be synthesized in the human body and must be supplied by the diet. In humans, tryptophan has relatively low tissue storage and the overall tryptophan concentration in the body is the lowest among all amino acids. Tryptophan plays a significant role for a multitude of metabolic functions and processes (e.g. syntheses of protein, serotonin, melatonin and NAD/NADP). Tryptophan is the sole precursor of serotonin and is distributed throughout the human body in the circulatory system (about 75-85% of tryptophan is bound to albumin). After uptake and metabolism, tryptophan is mainly excreted via urine and as metabolites kynurenine, kynurenic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, and xanthurenic acid can be determined.

For risk assessment purposes oral absorption of L-tryptophan is set at 100%. This assumption is based upon the physiological mechanisms of absorption. L-tryptophan is of low volatility due to a extremely low vapour pressure. From this and from the particle size it is not expected that L-tryptophan reaches the nasopharyncheal region or subsequently the tracheobronchial or pulmonary region in significant amounts. However, being a very hydrophilic substance with a low molecular mass any L-tryptophan reaching the lungs might be absorbed through aqueous pores. For risk assessment purposes, although it is unlikely that L-tryptophan will be available to a high extent after inhalation via the lungs due to the low vapour pressure, the inhalation absorption of L-tryptophan is set at 100%. L-tryptophan with high water solubility (11.4 g/L) and the log P value below 0 (-1.06) is expected to be too hydrophilic to cross the lipid rich environment of the stratum corneum. Therefore, for risk assessment purposes dermal absorption of L-tryptophan is set at 10%.