This summary information comes from Fass.
Persistence. Levothyroxine is potentially persistent.
Bioaccumulation. Levothyroxine has low potential for bioaccumulation.
Toxicity. Levothyroxine has low acute toxicity.
Risk. The use of levothyroxine (sales data Sweden 2018) has been considered to result in insignificant environmental risk.
Fass environmental information
Fass environmental information for Levaxin (levothyroxine) from Takeda Pharma (downloaded 2021-06-28).
Persistence: "Test results from "closed bottle test" (guideline 301 D) shows that the biological degradation is 0% in 28 days. Levothyroxine is potentially persistent."
Bioaccumulation: Log Pow = 2.4. "Since log Pow < 4, the substance has low potential for bioaccumulation."
Toxicity: There are data for 3 trophic levels, most sensitive crustacean (Daphnia magna), OECD 202, EC50 497 mg/L.
PEC/PNEC is based on sales data in Sweden in year 2018. PEC/PNEC = 0.00000444 which gives the risk insignificant.
Pharmaceutial residues in the aquatic environment
In the report Pharmaceutial residues in the Stockholm aquatic environment, levothyroxine was excluded on the grounds that it is "natural".
Author: Health and Medical Care Administration, Region Stockholm