TABLE OF CONTENTS

Title Page     –         –         –         –         –         –         –         –         –         i

Certification –         –         –         –         –         –         –         –         –         ii

Dedication    –         –         –         –         –         –         –         –         –         iii

Acknowledgements –         –         –         –         –         –         –         –         iv

Table of Content      –         –         –         –         –         –         –         –         v-vi

CHAPTER ONE

1.0     Introduction –         –         –         –         –         –         –         –         1-3

CHAPTER TWO

2.0     Heavy Metals in Soil          –         –         –         –         –         –         4-5

2.1     Factors Affecting Mobility and Bioavailability of Heavy metals in soil 6

2.1.1   Soil Organic Matter –         –         –         –         –         –         –         6-7

2.1.2   pH                –         –         –         –         –         –         –         –         7-8

2.1.3   Soil Texture –         –         –         –         –         –         –         –         8-9

2.1.4   Plant Species           –         –         –         –         –         –         –         10

2.2     Heavy Metals in Plant        –         –         –         –         –         –         10-12

2.3     Metal Uptake by Plants      –         –         –         –         –         –         12-13

CHAPTER THREE

3.0     Accumulation of Heavy Metals     –         –         –         –         –         14-17

3.1     Route of Heavy Metal uptake in Plants    –         –         –         –         17-18

3.2     Metal Toxicity and Tolerance in Plant     –         –         –         –         19-21

3.3     Effects of Plant factors on Bioaccumulation of Heavy Metals –          21-22

3.4     Health Hazard from Heavy Metal Exposure       –         –         –         23-26

CHAPTER FOUR

4.0     Summary and Conclusion   –         –         –         –         –         27

4.1     Summary      –         –         –         –         –         –         –         27

4.2     Recommendation    –         –         –         –         –         –         28

4.3     Conclusion    –         –         –         –         –         –         –         28

References

CHAPTER ONE

1.0     INTRODUCTION

Heavy metals have high density and mostly toxic in nature for human, plants, and animals regardless of their concentrations (LWTAP 2004) and have high atomic density five times greater than and have high atomic density five times greater than water or more than 4g/cm³ (Hawkes 1997) or more than 5g/cm³ (Saxena and Shekhawat 2013; Weast 1984). The nonessential metals are part of earth crust that enters the upper soil horizon and food chain through biogeochemical cycles (Tinsley 1979). Metals and metalloids such as Cadmium (Cd), Lead (Pb), Mercury, (Hg), Zinc (Zn) are called heavy metals because of their high densities (Oves et al., 2012), while Arsenic (As) is included in this list because of similar properties (Chen et al., 1999). Essential and nonessential trace elements, when exceed the threshold limits, can cause different physiological, morphological, and genetical anomalies including reduced growth, mutagenic effects, and increased, mortality (Luo et al., 2011).

Food crops are one of the important parts of our diet, and they may contain a number of essential and toxic metals (Waqas et al., 2015) depending on growing media characteristics. Vegetables are the major source of human exposure to heavy metal and contributed about 90% of the total metal intake, while the rest 10% intake occurs through dermal contacts and inhalation of contaminated dust (Khan et al., 2014). Food safety is burning issue regarding human health in the recent decades because of the high demand for food. This scenario leads to stimulate researchers and scientists to work on health risk associated with consumption of heavy metals, pesticides,and toxin-contaminated food (D’Mello 2003).

Soil characteristics play an important role interms of food production, and the contamination of this vital resource with heavy metals and their ultimate uptake and bioaccumulation in food crops possess major environmental and health problems particularly in developing countries (Lin et al., 2007). Soil type and plant genotype and their interaction have significant effect on heavy metal concentrations (Ding et al., 2013). Mineral fertilizers have higher heavy metal concentrations as compared to organic manure, therefore, the application of mineral fertilizers results in soil heavy metal pollution (Hu et al., 2013).

So far, a number of experiments (pot and field) have been conducted to study the effect of soil parameters and other elements on mobility and bioavailability of heavy metals from soil to crops system (Li et al., 2007; Hart et al., 2006). The mobility and bioavailability of heavy metals in contaminated soil is affected by a number of biological processes and physiochemical properties like soil pH, organic matter (OM) (Ahmad and Goni 2010, Ernst 1996; Alloway 1995), Cation Exchange Capacity (CEC), soil texture, and soil microbiota. Soil pH has significant effects on availability and accumulation of heavy metals in the edible parts of plants (Hu et al., 2013; Wang et al., 2013a). Similarly, CEC and OM have negative impact on the mobility and bioavailability of heavy metals like Pb (Arshad et al.,2008; Ding et al., 2013, MClaughlin et al., 2011, Khan et al., 2015). Cd toxicity to the soil environment is well known, it is a toxic heavy metal and causes toxicity even at low concentration. The bioaccumulation rate of Cd is higher in the field crops as compared to other elements (Moustakas et al., 2001; Aarao and Ae 2003).

The associated health hazards of toxic metal depend on concentrations of these metals in specific media and exposure time. Long time and chronic exposure can cause health hazards even at low concentrations of toxic metal (Mahalakshmi et al., 2012). Among the abiotic stresses to plants, and the toxicity is based on physiochemical properties of heavy metals (Saxena and Sekhawat 2013; Zhuang et al., 2009).