Ecotoxicity tests with Allium cepa to determine the efficiency of rice husk ash in the treatment of groundwater contaminated with benzene, toluene, ethylbenzene, and xylene

Abstract

The validation of adsorption treatment based on toxicity assays aims to assess the actual environmental impact caused by effluents after treatment. This study describes the use of rice husk ash as adsorbent and evaluates the efficiency of adsorption treatment to remediate groundwater contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX). The synthetic effluent was prepared with standard benzene, toluene, ethylbenzene, and xylene solutions. Adsorption was assessed at treatment times 0, 60, 120, and 240 min. Compounds were quantified by gas chromatography with flame ionization detector. The treatment was validated based on ecotoxicity assays using Allium cepa as indicator organism. For the treatment times stipulated, samples containing 25, 50, and 100% of BTEX were used. The dilutions were carried out with drinking water according to Fiskesjö (1985). The relative growth index (RGI), root inhibition index (Ii), and germination index (GI) confirmed the efficiency of the treatment approach tested. The best adsorption time for an initial BTEX concentration of 3.378 mg/L was 60 min. Critical level (EC50) and critical concentration that induced phytotoxic effect on A. cepa germination was observed only for the undiluted effluent.

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