Toxicity assessment of industrial effluent by bioassays

In the present study, the toxicity assessment of tannery effluent was carried out in terms of percent phytotoxicity and shoot/root dry weight ratio. The effluent used in the study was collected from the outlet of an effluent treatment plant situated in the Jajmau area of Kanpur, U. P. India. Three varieties each of rice (Surya-52, Jaya-14 and Pant-10), pulses (Lens-(Type-9), Gram Bahar, and Mung-C-K-851) and oil seeds (Mustard RS-30, B-9 and T-69) containing different kinds of reserve food materials, i.e., starch, protein and fat were taken for the toxicity study. The accumulations of heavy metals, i.e., Cr, Cu, Zn, and Ni, by these different crop varieties through pot culture irrigated with effluent were estimated at maturity. The concentration of heavy metals in the effluent was found to be Cr = 0.135, Cu = 0.065, Zn = 0.052, and Ni = 0.036 mg/L. The maximum concentration found in the plant tissue was seen in the mustard variety RS 30, i.e., Cr = 15.2, Cu = 4.4, Zn = 3.2, and Ni = 2.6 mu g/g dry weight (d.w.) and the minimum concentration was found in Gram Bahar, i.e., Cr = 8.5, Cu = 2.0, Zn = 1.6 mu g/g d.w., whereas, in 0.98 mu g/g d.w. of Ni was found in the Surya rice variety. The percent phytotoxicity was found to be in the range of 10.4 to 25.6% amongst the different test varieties. The average percent phytotoxicity was found to be highest in rice followed by oilseed and pulses. The shoot/root dry weight ratio ranged between 10.82 to 14.22, with the highest value seen for rice (Pant-10) and the lowest for a pulse (Gram-Bahar). The results revealed that cultivation of these crops irrigated with the tannery effluent may pose a potential risk to humans as well as animals because of their bioaccumulation properties and ability to transfer metals from one trophic level to the next trophic level through the food chain. Since the percent phytotoxicity and shoot/root dry weight ratio behaves in a similar manner for the effluent, these parameters can be considered for the assessment of toxicity of industrial effluents.