Perfluorooctanoic acid (PFOA) is an anthropogenic contaminant detected in various environmental and biological matrices. This compound is a fluorinated surfactant, belonging to a class of molecules known for persistence and their global distribution, but for which little ecotoxicological data are currently available, especially under field conditions. The environmental fate and toxicity of PFOA to the aquatic macrophytes Myriophyllum sibiricum and M. spicatum were investigated using 12,000 L outdoor microcosms. Replicate microcosms (n = 3) were treated with 0.3, 1, 30, and 100 mg/L PFOA as the sodium salt, plus controls, and assessed at regular intervals over 35 days. PFOA showed no significant dissipation from the water column, except at the greatest concentration, where partitioning from the water column into other compartments is suspected. The two species of Myriophyllum were similar in their sensitivity to PFOA under these simulated field conditions. Toxicity after 14 to 35 days of exposure in the evaluated endpoints for M. spicatum was > or = 5.7 mg/L PFOA for EC10s and > or = 31.8 mg/L PFOA for EC50s and in M. sibiricum was > or = 8.4 mg/L PFOA for EC10s and > or = 35.8 mg/L PFOA for EC50s. The no observed effects concentrations (NOECs) for Myriophyllum spp. were consistently > or = 23.9 mg/L PFOA. A risk assessment for these plant species estimated a negligible probability of toxicity being observed from PFOA exposure at current environmental concentrations.