Resumo. Abstract Aim: Leaching from mining activities reaches water bodies, causing water contamination and acidification by toxic metals. As a consequence, oxygen depletion occurs, with the disappearance of certain benthic organisms, losses in phytoplankton and zooplankton biomass, and fish mortality. Remediation of contaminated water from mining involves the use of flocculants based on acrylamide monomers and polyacrylamide and of coagulants based on aluminum. Our aim was to assess the aquatic toxicity of the flocculant WF 424 and the coagulant WF 2000 PCA. Methods A flocculant anionic polymer (WF 424) and a coagulant polynuclear complex of polymerized hydro-aluminum ions (WF2000 PCA) were tested for embryotoxicity to zebrafish (Danio rerio, FET test - OEDC, 236, 2013). Results After 96 h of exposure to WF424, there was no significant lethality, nor were there sublethal effects such as hatching delay, heartbeat alteration, and malformation in embryonic development, when compared with the control group (p > 0.05). The coagulant compound WF2000 PCA did not show lethal effects during 96 h of exposure, and EC50 was considered as above the highest concentration-level tested. Conclusions For both compounds, no malformation, embryonic development delay or embryotoxicity were observed.