The T-value in the score for hazard refers to chronic toxicity. Underlying data for P, B, T and risk are from Fass.
Fass environmental information for Femar (letrozole) (downloaded 2019-02-08).
Persistence: "1 % degradation in 29 days, not readily biodegradable (OECD 301B). [---] Letrozole does not pass the criteria for ready biodegradation. The phrase “Letrozole is potentially persistent” is thus chosen."
Bioaccumulation: Log Kow = 1.73 (experimentally determined, method unknown).
Toxicity: There are data for 3 trophic levels, most sensitive fish (Oryzias latipes) NOEC 5 microg/L.
PEC/PNEC is based on sales data in Sweden in year 2015. PEC/PNEC = 0.02 which gives the risk insignificant.
Author: The Pharmaceutical unit of Region Stockholm