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Persistence. Letrozole is potentially persistent.

Bioaccumulation. Letrozole has low potential for bioaccumulation.

Toxicity. Letrozole has very high chronic toxicity.

Risk. The use of letrozole (sales data Sweden 2018) has been considered to result in insignificant environmental risk.


This summary information comes from Fass.

Fass environmental information

Fass environmental information for Femar (letrozole) from Novartis (downloaded 2023-06-28).


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).

Chronic toxicity: There are data for 3 trophic levels, fish (Oryzias latipes) NOEC 5 microg/L.


PEC/PNEC is based on sales data in Sweden in year 2018. PEC/PNEC = 0.03 which gives the risk insignificant.

Author: Health and Medical Care Administration, Region Stockholm