This summary information comes from Fass.
Persistence. Rifaximin is persistent.
Bioaccumulation. Rifaximin has low potential for bioaccumulation.
Toxicity. Rifaximin has very high chronic toxicity.
Risk. The use of rifaximin (sales data Sweden 2018) has been considered to result in low environmental risk.
Fass environmental information for Xifaxan (rifaximin) from Norgine (downloaded 2021-01-21).
Persistence: "Ready degradability: The mean cumulative carbon dioxide production by mixtures containing rifaximin was negligible (equivalent to 1% of the theoretical CO2 production) at the end of the test on day 29. Degradation of the reference substance sodium benzoate was similar both in the presence and absence of rifaximin, which confirmed that the activity of the microbial inocula was not inhibited. Since the test mixtures are likely to have contained both rifaximin and its hydrolysis products, the result of this test indicates that rifaximin was neither readily biodegradable nor inhibitory to the activity of the bacterial inoculum. [---] Substance rifaximin does not pass the ready degradability test. The phrase “Rifaximin is potentially persistent” is thus chosen." The database, Pharmaceuticals and Environment, reference group believes that based on these results, a drug substance is persistent and not potentially persistent, hence the information that rifaximin is persistent in the initial summary information.
Bioaccumulation: Log Kow = 2.76 at pH 7 (OECD 117).
Chronic toxicity: There are data for 3 trophic levels, most sensitive algae "NOEC 72 h (biomass, growth) = 0.76 microg/L (OECD 201)."
PEC/PNEC is based on sales data in Sweden in year 2018. PEC/PNEC = 0.26 which gives the risk low.
Author: Health and Medical Care Administration, Region Stockholm