a b s t r ac tIn this study, the removal of brilliant green dye from aqueous solution using seaweed Sargassum wightii was carried out. The effects of different variables such as adsorbent dose, pH, initial dye concentrations and temperature were studied through batch experimental system. The adsorbent-adsorbate interaction was characterized by Fourier transform infrared spectroscopy and UV-Vis spectrophotometer and the surface structure of the sorbent was documented by scanning electron microscopy and chemical composition was determined by energy dispersive X-ray spectroscopy. The maximum biosorption of brilliant green dye was observed at the sorbent concentration of 0.1 g/L, 7 of pH at 35°C of temperature and initial dye concentration of 10 mg/L. Sorption interaction of dye on to algal biosorbents obeyed the pseudo-second-order rate (R 2 = 0.99). Experimental data showed good fit with the Langmuir adsorption isotherm (R 2 = 0.996) model with a maximum biosorption capacity of 43.48 mg/g. Furthermore, significant reduction in physicochemical parameters was obtained in the treated dye compared with the untreated dye. Phytotoxicity analyses suggested that the treated dye could be tuned as beneficial source for agricultural practices. Accordingly macroalga could be utilized as an efficient adsorbent for dye removal from aqueous solution; prompting to resulting subsequent reduction of toxic effects of the treated dye, alleviates environment damage.

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Seaweed Sargassum wightii is one of the most important marine resources as they have biological activity. Numerous researchers have reported on brilliant green dye decolourization using various seaweed. Despite its impact on after treatment, little information is available on the effect of seaweed-treated dye toxicity against plants and microorganisms. The present investigation was carried out to assess the microbial toxicity of S. wightii-treated and untreated dye using various microorganisms and cytotoxicity effect on Allium cepa L. In this study, untreated dye which has substantial amount of the colour in it exhibited significant toxic effect against major gram-positive and gram-negative bacteria. The clear zone of inhibition exhibited by the untreated dye around bacterial and fungal colonies reflects its extent of microbial toxicity and infers that the untreated dye has antibacterial and antifungal activity. No inhibition zones were observed with treated dye when compared with the untreated dye. Consequently, treated dye does not exhibit microbial toxicity due to the complete absence of the dye in it. Cytotoxicity study on A. cepa grown in untreated dye solution showed decrease in root growth, increase in the mitotic index and chromosomal damage, whereas A. cepa bulbs grown in seaweed-treated dye showed betterment in root growth, increase in the mitotic index and decrease in chromosomal damage. Results of the cytotoxicity study indicated the untreated dye solution exerts toxic effect on A. cepa, whereas treated dye solution did not pose any toxic effect. This indirectly proves the efficiency of marine algae in complete removal of the dye from the present study. Thus, worldwide awareness of dye removal from aqueous solution and its management could be provoked.