Toxicity Assessment of Pre- and Post-treated Dye Wastewater Using Allium cepa Assay

Wastewater treatment is important because of the adverse effects the contaminants may cause in the environment. The toxicity of wastewater before and after treatment needs to be ascertained, so that its safe reuse can be ensured and guaranteed. In this study, the toxicity of Malachite green (MG) and Methylene blue (MB) wastewater before and after treatment with Moringa oleifera seed husk (MOSH) following the adsorption method was assessed using the Allium cepa (Onion bulbs) assay. Seven onion bulbs were planted in different MB and MG solutions (10, 30 and 60 ppm) before and after treatment for 72 h. These were also planted in distilled water as negative control. The roots of the onion bulbs were harvested after 72 h and measured with a ruler. EC40 (effective concentration at 40%) and EC50 (effective concentration at 50%) of the root growth (RG) in the solutions were calculated. The mean root length in the negative control was significantly higher than the mean root length from MB and MG solutions before adsorption. The variation range of mean root length of onion bulbs planted in post-treated MG solution (0.47–0.89 cm) was higher than in post-treated MB solution (0.77–0.98 cm). The EC40 of MG before and after treatment was 12 and 22 ppm, while the EC50 of MB was 39 and 25 ppm, respectively. This suggests that more cell divisions occurred in the MG solution after treatment. Therefore, the adsorption treatment method used in this study was more effective in reducing the toxicity of MG solution than that of MB.