There is no data for the T-value. The environmental information comes from Fass.se.
Fass environmental information for Circadin (melatonin) (downloaded 2018-07-03).
Persistence: Data not available.
Bioaccumulation: Log Pow = 1.65.
Chronic toxicity: Data not available.
"Risk of environmental impact of melatonin cannot be excluded, since there is not sufficient ecotoxicity data available."
assessment report for Circadin (melatonin) EMEA/H/C/695. "PECsurface water 0.00002 μg/L. The correct value is above the trigger value of 0.01 μg/l and therefore phase II studies are in principle needed. The applicant was requested to discuss the need for such studies. The re-calculated the PEC surface water on the basis of the new posology (2 mg/day) and the administration schedule proposed (3 weeks followed by 2 months interval, resulting in 15 weeks of exposure), resulted in a value below the trigger limit. Therefore further phase II studies were not requested by the CHMP considering that Circadin, at the recommended posology, did not present any potential risk to the environment."
Author: The Pharmaceutical unit of Region Stockholm