Abstract:
Tubificid worms, a popular live fish food are commonly found in the sediment-water interface in heavy metal contaminated habitats. These are also widely used as a test organism for evaluating aquatic environmental health. However, the toxic potential of metals can hinder the potential of these worms as safe live fish food as well as pose threat to other organisms through bioaccumulation in successive trophic levels. In the present study, acute toxicity and bioaccumulation of three commonly occurred heavy metals in polluted water, namely, cadmium (Cd2+), chromium (Cr6+) and lead (Pb2+) were evaluated in Tubifex spp. The worms were exposed to various concentrations of these three metals in water only static acute toxicity tests for each metal separately. The concentration-mortality (%) data were analyzed through graphical analysis and Probit analysis to estimate the 96 h median lethal concentration (LC50). The worms were subjected to sub-lethal concentration for 96 h and periodic accumulated metal were measured using Atomic Absorption Spectrophotometer. The worms showed various behavioral responses including increased movement, decreased clumping tendency and mucus secretion with increasing metal concentrations and exposure duration. Posterior part of the body was most affected resulting in random loss of hind parts and tail bifurcation at high concentrations. Cd2+ was found to be the most toxic followed by Cr6+ and Pb2+ with LC50values 0.0762, 1.4995, 1.8799µM respectively. In contrast, order of bioaccumulation (ppm) was Pb2+ >Cd2+ >Cr6+. The accumulation increased up to 72 h and decreased afterwards which supports the responses and mortality trend observed. The current study confirms that metal toxicity to Tubifex spp.varies among different regions as reported in other studies and should be evaluated accordingly. This study found both the linear model from Probit analysis and 4 parameter sigmoid model are suitable (R2>0.95) to predict the toxicity endpoints in Tubifex spp. The findings of this study can provide crucial information to establish water and sediment quality guidelines, and also can provide toxicological understanding essential in the mass production of Tubifex spp. as live fish food under polluted environment.
