The toxicity of ibuprofen and perfluorooctanoic acid (PFOA) was evaluated individually and in binary combination on two photosynthetic organisms, the green alga Pseudokirchneriella subcapitata, representative of aquatic environments, and the monocotyledonous Sorghum bicolor, for terrestrial ecosystems. Both non-target organisms showed different sensitivities to pollutants. The alga was more affected than the plant to each compound assayed, whether separately or mixed in EC50 proportion, and PFOA was more toxic to both bioindicators. An analysis of toxic chemical interactions covering the whole range of effect levels was conducted using the Combination Index method and indicated that synergism could be expected at low effect levels in higher plants, while for algae this type of interaction predominated at higher effect levels. Ecological risk assessment was performed by calculating the Hazard Quotient as the ratio between the measured environmental concentration and the predicted no-effect concentration, using our EC50 data derived from the mixture of pollutants. Acute hazard was found in the terrestrial compartment (soil or sediments). In the light of the data reported, we conclude that risk evaluation should include toxicological information on compound interactions that exert a toxic effect on non-target organisms.