BECAUSE of their refractory nature, chlorofluorocarbons (CFCs) released by industries are eventually transported to the stratosphere, where they are slowly degraded by solar ultraviolet radiation into highly reactive chlorine atoms which can then participate in a catalytic ozone depletion cycle. For this reason, signatories to the Montreal Protocol and subsequent amendments have agreed to phase out the use of CFCs1 in the next few decades. Hydrofluorocarbons acid hydrochlorofluorocarbons have been proposed as CFC replacements; atmospheric degradation of several of these is expected to produce trifluoroacetate (TFA), which is removed from the atmosphere mainly by rain(2,3). The global average TFA concentration in rain water for the year 2010 is estimated(4) to be 0.16 mu g l(-1)-well below the concentrations thought to inhibit plant growth (similar to 10(2)-10(6) mu g l(-1))(5). But our modelling analysis, presented here, indicates that in conditions of high evapotranspiration, TFA could attain appreciable concentrations (>10(2) mu g l(-1)) in the local surface waters of seasonal wetlands within a few decades, if removal by degradation and seepage is limited.