The T-value in the score for hazard refers to chronic toxicity. Underlying data for P, B and T comes from Fass.se, see below.
Desogestrel is converted in the body into the active metabolite etonogestrel. The PBT value therefore refers to etonogestrel. Measurements of etonogestrel in the environment are lacking.
Etonogestrel has approximately the same ability to bind to the androgen receptor in fish as levonorgestrel. A substance's ability to activate the androgen receptor in fish is believed to contribute to increased risk of environmental impact. Etonogestrel also binds to SHBG (Sex Hormone Binding Globulin). Binding to SHBG is believed to contribute to increased bioconcentration (and thus potency) in fish. Based on this, it can be assumed that there is a risk associated with the use of etonogestrel/desogestrel and that these substances appear additive with other androgenic gestagens in the environment.
Fass environmental information for Cerazette (desogestrel) (downloaded 2018-07-02).
Persistence: "Sediment Transformation (OECD 308): DT50 (total system) = 9.2 to 50 days."
Bioaccumulation: "Log Kow = 3.5. Bioaccumulation (OECD 305): Flow through study with Bluegill sunfish (Lepomis macrochirus) Lipid normalized kinetic BCF = 128."
Chronic toxicity: There is NOEC for 3 trophic levels, lowest NOEC for fish (Oryzias latipes) 2.7 nanog/L.
PEC/PNEC is based on sales data in Sweden in year 2016. PEC/PNEC = 2 which gives the risk moderate.
Author: Health and Medical Care Administration, Region Stockholm