The comparative fates and effects of salicylic acid (SA) and Na salicylate in algae (Scenedesmus subspicatus, Monoraphidium minutum), in Lemna minor, and in Daphnia magna were examined. Test methods were principally based on the OECD testing guidelines with modifications in the procedures. The influence of fulvic acid (FA) on bioconcentration and on toxic effects was studied. FA addition significantly reduced the bioavailability of SA in L. minor and the algae species. SA was more toxic to Lemnaceae, algae, and daphnids than to its Na salt. Bioconcentration factors in S. subspicatus, M. minutum, and L. minor were about 10(3) in 72-96 hr. The reproducibility of D. magna was reduced by 38% at a concentration of 20 mg SA/liter.