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 Zofran (ondansetron) (downloaded 2019-01-16).
Persistence: "Inherent degradability: 19% degradation in 28 days (OECD 302). Soil Metabolism: 20-99.9% degradation in 64 days (TAD 3.12). Hydrolysis: 50% degradation (pH 7) > 1 year (TAD 3.09). Ondansetron is not readily degradable nor inherently biodegradable. The phrase “Ondansetron is potentially persistent” is thus chosen."
Bioaccumulation: "Log Dow at pH 5 = 0.23, Log Dow at pH 7 = 1.00, Log Dow at pH 9 = 1.26."
Toxicity: There are data for 3 trophic levels, most sensitive crustacean (Ceriodaphnia dubia) NOEC chronic toxicity 320 microg/L.
PEC/PNEC is based on sales data in Sweden in year 2015. "PNEC (μg/L) = lowest NOEC/100, where 100 is the assessment factor applied for two long-term NOECs when such results have not been generated from that showing the lowest L(E)C50 of the short-term tests. The lowest NOEC for water flea (= 320 μg/L) has been used for this calculation since it is the most sensitive of the two tested species." PEC/PNEC = 0,0007 which gives the risk insignificant. ECHA's guidelines state that AF 50 should be used for data for two long-term studies. If AF 50 is used, the risk is also insignificant (PEC / PNEC = 0.00035).
Author: Health and Medical Care Administration, Region Stockholm