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Evaluation of phytotoxicity of coir pith black liquor generated by oxidative delignification process to Oryza sativa L

R.Syamkumar, G.Rojith, S.Rajathy, I.S.Bright Singh

Coir pith is a polyphenol containing agroindustrial residue which causes land and water pollution. Research programs are advancing by utilising coir pith as a substrate for bio energy production, and oxidative delignificationwas reported as an effective pretreatmentmethod. Oxidative delignification process generates highly coloured ‘Coir pith Black Liquor’ (CBL) as effluent and its release to open environment poses pollution risks. Evaluation of toxicity of CBL is of significance for its safe disposal plans. In the present study, we investigated the phytotoxicity of CBL to a standard test species Oryza sativa. A 96 hour bioassay was conducted. Root length, shoot length, seed germination, Germination Index (GI), Seed Vigor Index (SVI) and Shoot toRoot ratio (S:R)were the parameters studied. Data acquisition was done with the help of image analysis software ‘Fiji’. Statistical analysis was carried out using ‘R’ software. The EC50 (Median Effective Concentration), the concentration at which 50% reduction in growth, compared to control, occurred was calculated for each parameter. The EC50s were converted into Toxic Units (TU) for comparison. All parameters studied were significantly affected by the CBL. The study revealed that CBL was acutely toxic to Oryza sativa. Root length and Germination Index (GI) were the most sensitive endpoints (TUs = 8.9 and 8.8 respectively) whereas seed germinationwas the least sensitive endpoint (TU = 1.73). Based on sensitivity, the parameters were arranged as : Root length=GI>Seedling length=SVI>Shoot length>Germination. The results points towards the necessity of further characterization of toxicants present in the CBL and treatment procedures to eliminate the toxicity.