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Abstract. Coal mining produces residues containing high levels of heavy metals and other components that contaminate surface and ground water. This research evaluated the efficiency of physical, chemical, and biological treatment of acid mine drainage using alternative biological indicators Artemia sp. (brine shrimp) and Allium cepa L. (onion). Samples were collected at four stations that are located at specific treatment system: 1) pH control and precipitation, 2) biological damping pond outlet, 3) wetland inlet, and 4) wetland outlet. Acute toxicity analysis using Artemia sp. was performed at sample concentrations of 25, 50, 80, 90, and 100%. Toxicity in A. cepa was observed as root growth inhibition after a seven-day exposure period at 100% effluent concentration. Genotoxicity was observed in A. cepa meristematic cells using the comet assay that evaluates DNA strand breaks in single cells. Artemia sp. test results indicated a reduction of lethality in station 4 (less than 30%) when compared to station 3 (100%), indicating that the wetland is effective at reducing residue toxicity for these organisms. The high lethality at Station 3 was investigated and resulted in the discovery that contaminated ground water from residue leachate was entering the treatment system between Stations 2 and 3. Root growth inhibition showed no significant results, indicating that the effluent has no activity to A. cepa considering this parameter. The comet assay results indicate that stations 1 and 2 are genotoxic and a significant reduction can be observed after the biological processes, particularly at the wetland output. Thus, the results obtained indicate that Artemia sp. is a suitable bioindicator for toxicity assays of this effluent and that A. cepa is only suitable for evaluating genotoxicity. We can also observe that the treatment process is efficient at eliminating effluent toxicity and reducing genotoxicity. Additional

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