Toxicological Analysis of Acid Mine Drainage by Water Quality and Land Use Bioassays

AMD toxicity was evaluated using water quality and land use bioassays. In particular, we determined concentrations for lethal and sublethal effects as part of the risk assessment process. Lactuca sativa (lettuce), Raphanus sativus (radish), and Triticum aestivum (wheat) were used to predict phytotoxic effects caused by metals, as oxidative stress inhibits germination. The results, expressed as the fraction of AMD resulting in 50% lethality (LC50) at 144 h, showed that wheat was more tolerant (LC50 = 62%) than radish (LC50 = 17.0%) or lettuce (LC50 = 21%). The AMD was found to be very toxic to Daphnia magna (cladoceran) and Danio rerio (zebrafish) embryos, two of the best model organisms in aquatic ecology and ecotoxicology (LC50 < 1%). However, when EDTA was used to chelate the metals, the animal toxicity effects was essentially eliminated, pointing to metal content as the main driver of toxicity. Analysis of two molecular biomarkers for an organic pollutant's toxicity, cyp19a1b and cyp1a, showed no activation of either gene, further indicating that the toxicity was mainly associated with the metals. The results also suggest that the environmental risk associated with the AMD could be largely mitigated by relatively cheap and simple measures to reduce metal mobility, like liming.