Toxicity Analysis of Effluent Released During Recovery of Metals from Polymetallic Sea Nodules Using Fish Haematological Parameters

Abstract

To meet its domestic demands India has to import many of the economically important metals like Manganese, Iron, Cobalt, Zinc, Nickel and others. As the land based resources of these metals are depleting very fast, considerable efforts have been made to extract metals from pollymetallic sea nodules (PMN) during the past four decades all over the world. To attain self sufficiency scientists at National Metallurgical Laboratory, Council of Scientific and Industrial Research, Jamshedpur, India has developed an indigenous process to recover some of these metals from PMN. The PMN are rock concretions on the sea bottom formed of concentric layer of iron and manganese hydroxides around their core. They are small, slightly flattened, dark-brown coloured balls measuring 5 to 10 centimeters in diameters. The chemical composition of the nodules varies considerably according to the kind of minerals and the size and characteristics of the core. Those of the greatest economic interest contain Mn (27-30%), Ni (1.25-1.5%), Cu (1-1.4%), and Cobalt (0.2-0.25%). Other constituents include Fe (6%), Si (5%), Al (3%) with lesser amounts of Ca, Na, Mg, K, Ti, and Ba along with hydrogen and oxygen. For metal extraction purpose nodules are dried at 1100 C, grounded and treated with reducing agents, followed by ammonia leaching. Separation of metals is done by the process of solvent extraction and electrowining (Jana et al., 1990; Kumar et al., 1990; Agarwal & Goodrich, 2008; Biswas et al., 2009). During the process of metal recovery highly contaminated effluent is generated that still retains substantial amount of metals (Vaseem & Banerjee, 2011a). These metals are highly toxic and are one of the main causes of environmental pollution. Two most important factors that contribute to the deleterious effects of heavy metals as pollutants are their non-degradation in the nature (unlike organic pollutants) and their tendency to bioconcentrate and settle at the bottom of water bodies. Hence our main aim has been to monitor the toxicity rendered to the aquatic ecosystem by this highly contaminated effluent (Table 1) using fish as an experimental model. Labeo rohita (commonly known as Rohu), a major Indian carp of great nutritional importance has been selected for the toxicity analyses of the effluent because fishes have widely been used as effective bioindicator. This graceful Indo-Gangetic riverine species is one of the three important major carps of the Indian subcontinent belonging to the family cyprinidae. It is the natural inhabitant of the wetlands of northern and central India, and the rivers of Pakistan, Bangladesh and Myanmar. It is a diurnal, herbivore and generally