CHAPTER ONE

INTRODUCTION 1.1 Background to the study Uptake of heavy metals by plants and subsequent accumulation along the food chain is a potential threat to animal and human health (Sprynskyy et al., 2007). The absorption by plant roots is one of the main routes of entrance of heavy metals in the food chain (Jorda, 2006). Absorption and accumulation of heavy metals in plant tissue depend upon many factors which include temperature, moisture, organic matter, pH and nutrient availability. Heavy metal accumulation in plants depends upon plant species and the efficiency of different plants in absorbing metals is evaluated by either plant uptake or soil to plant transfer factors of the metals (Khan et al., 2008). For example, elevated Pb levels in soils may decrease soil productivity, and a very low Pb concentration may inhibit some vital plant processes, such as photosynthesis, mitosis and water absorption with toxic symptoms of dark green leaves, wilting of older leaves, stunted foliage and brown short roots (Bhattacharyya et al., 2008). Heavy metals are potentially toxic and phytotoxicity for plants result in chlorosis, weak plant growth, yield depression, and may even be accompanied by reduced nutrient uptake, disorders in plant metabolism and reduced ability to fixate molecular nitrogen in leguminous plants (Guala et al., 2010). Seed germination was found to be gradually delayed in the presence of increasing concentration of lead and have been due to prolonged incubation of the seeds that resulted from the neutralization of the toxic effects of lead by some mechanisms e.g. leaching, chelation, metal binding and/or accumulation by microorganism (Ashraf and Ali, 2008) .The plant uptake of heavy metals from soils at high concentrations may result in a great health risk taking into consideration food-chain implications.

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