The T-value in the score for hazard refers to acute toxicity. Underlying data for B and T are from Fass environmental information for Tibinide (isoniazid) Meda downloaded 2019-04-01. Underlying data for P comes from Fass's environmental information for Tibinide (isoniazid) Meda downloaded 2011-03-14. The risk is from Fass's environmental information for Tibinide downloaded 2019-04-01.
Fass environmental information for Tibinide from Meda (downloaded 2019-04-01 and 2011-03-14).
Persistence: No data (Fass 2019-04-01). Isoniazid degrades slowly in the environment. 12.5 % degradation after 28 days (OECD 301F). This does not necessarily mean that the substance is degraded at the same rate under natural conditions, but it indicates that further studies need to be done to determine degradability (Fass 2011-03-14).
Bioaccumulation: "An experimentally derived Log Kow of -0,70 (unknown method) ... indicates that isoniazid has low potential for bioaccumulation" (Fass downloaded 2019-04-01).
Toxicity: In Fass 2019-04-01 there are data for one trophic level, crustaceans (Daphnia magna) (OECD 202) EC50 24 hours (immobility): 406 microg/L. In Fass 2011-03-14 there are data for 3 trophic levels, most sensitive green algae (Pseudokirchneriella subcapitata) (OECD 201) EC50 = 23,500 microg/L.
Risk of environmental impact of isoniazid cannot be excluded, since no ecotoxicity data are available according to Fass downloaded 2019-04-01.
PEC/PNEC based on sales data (193.94 kg) in Sweden in 2015 according to Fass environmental information for Tibinide downloaded 2019-04-02. PEC is set to 0.03 microg/L. PNEC (Fass environmental information for Tibinide downloaded 2011-03-14) = 23.5 microg/L (for green algae and AF 1000). PEC / PNEC = 0.00128 which gives the risk insignificant. In selection of algae for toxicity testing of antimicrobials the European Medicines Agency, EMA, recommends test on blue-green algae (cyanobacteria). No information on toxicity on blue-green algae has been found, which means that a calculation of environmental risk becomes uncertain.
Author: The Pharmaceutical unit of Region Stockholm