DETERMINATION OF HEAVY METALS AND ANTI-NUTRITIONAL CONTENTS OF IRRIGATION WATER AND SOME SELECTED VEGETABLES GROWN IN JAKARA KANO STATE

Introduction 1.1 Background of the Study The problem of environmental pollution due to toxic metals has begun to cause concern now in most major metropolitan cities. The toxic heavy metals entering the ecosystem may lead to geoaccumulation and bioaccumulation (Lokeshwari and Chandrappa, 2006). The use of water from non-conventional resources like polluted water of industrial and household discharge is a common practice in most African countries that are facing the problem of water shortage (AlAnsari et al., 2013). This uncontrolled irrigation of crops with sewage water leads to the accumulation of some potentially toxic metals in agricultural soil and have very adverse effects on the growth of the plants (Muhammad et al., 2013). It is now a common practice in many parts of Nigeria to use municipal sewage water that contain both industrial effluents and domestic liquid waste for irrigation purpose (Alexander and Ubandoma, 2014; Odoh and Kolawole, 2011). This waste water contains few important plants growth nutrients like potassium (K), zinc (Zn), phosphorus (P), nitrogen (N), and organic solids (Gibbs et al., 2006). Whereas it is also the prime source of potentially hazardous organic and inorganic toxic materials. Heavy metals like Iron (Fe), Copper (Cu), Ni and other trace elements are important for proper functional of biological systems and their deficiency or excess could lead to a number of disorders. Food chain contamination by heavy metals has become a burning issue in recent years because of their potential accumulation in bio-systems through contaminated water, soil and air (Lokeshwani and Chandrappa, 2006). 2 Therefore, a better understanding of heavy metal sources, their accumulation in the soil and the effect of their presence in water and soil on plants system seem to be particularly important for researches on risk assessment (Rajesh et al., 2004). Many studies have shown that sewage water irrigation has elevated the levels of toxic heavy metals such as nickel (Ni), Zn, cobalt (Co), manganese (Mn), and Fe in receiving soil (Ali et al., 1996; Singh et al., 2004; Mapanda et al., 2005), and after that vegetables take up metals by absorbing them from that contaminated soils, as well as from deposits on different parts of the vegetables exposed to the air from polluted environments (Oluwole et al., 2013). Spinach is just like other vegetable plant used as food and constitute an important part of human diet because is rich in carbohydrate, protein, as well as vitamins, minerals and trace elements (Oluwole et al., 2013). They are also made up of chiefly cellulose, hemi-cellulose and pectin substances that give them their texture and firmness (Sobukola and Dairo, 2007). Eating vegetables regularly in diet can have many health benefits by reducing diseases and used to convert fats and carbohydrates into energy (Mercola, 2014). Also, eating vegetables is one of the most important pathways for the human body to absorb dietary minerals necessary for healthy development, but unfortunately harmful elements such as heavy metals may lead to intoxication due to prolong accumulation found in these vegetables (Elsevier, 2008). Some of these metals after accumulating in the soil are transferred to food chain which can cause serious health hazards to human beings and animals. Besides, metals induce deficiency of other nutrients like Cu, Fe and Mn by inhibiting plant uptake of Zn, possibly because of competition for the same carrier site in soil-water system (Rashid and Salim, 1988). Metals like Fe, Mn, Co, Cu, and Ni are essential nutrients but their permissible limits are quite low in living organism (Qadir et al., 1999).