1.0 INTRODUCTION
Heavy metals are defined as elements in the periodic table having
atomic number more than 20 or densities more than 5g/cm3 generally
excluding alkali metals and alkaline earth metals. The environmental
problems with heavy metals are that they as elements are undestroyable
and the most of them have toxic effects on living organisms when
exceeding a certain concentration. Furthermore, some heavy metals are
being subjected to bioaccumulation and may pose a risk to human health
when transferred to the food chain. Soils, whether in urban or
agricultural areas represent a major sink for metals released into the
environment from a wide variety of anthropogenic sources (Niragu,
1991).
Soil pollution by heavy metals is a significant environmental
problem worldwide (Alloway, 1995). In particular heavy metal pollution
of surface soils due to intense industrialization and urbanization has
become a serious concern in many developing countries (Mireless et al,
2012). The accumulation of heavy metals in surface soils is affected by
many environmental variables, including parent material and soil
properties, as well as by human activities, such as industrial production,
traffic, farming and irrigation.
Large areas of land can be contaminated by heavy metals released
from waste incinerators, industrial wastes and from the application of
municipal compost, pesticides and fertilizers irrespective of their sources
in the soil, accumulation of heavy metals can degrade soil quality, thus
negatively impact the health of human, animals and the ecosystem
(Nagajyoti et al, 2010). It is important to identify the sources of heavy
metals, besides quantifying their concentrations and spatial variability in
the soils.

Once in soil, some of these metals would be persistent because of
their fairly immobile nature. Other metals however would be more
mobile therefore the potential of transfer either through soil profile down
to ground water aquifer or via plant – root uptake (bio available) is likely.
When the food chain is concerned, one has to take into account the
mobility and the bio availability of metals, because plant uptake of metals
parallels the bio available fractions of the metals in soil.

In most soil environment sorption is the dominating speciation
process and thus the largest fraction of heavy metal in a soil is associated
with solid phase of that soil. Pollution problem arise when heavy metals
are mobilized into the soil solution and taken up by plants or transported
to the surface ground water. The properties of the soil are thus very
important in the attenuation of heavy metals in the environment. The
solubility of heavy metals in soil is controlled by reactions with solid
phases. Once sewage sludge is applied to soil, the heavy metal species
undergo several possible fates including:
(i) Absorption/desorption reactions
(ii) Precipitation/dissolution reaction
(iii) Plant uptake and
(iv) A possible mobility through soil profile

1.1 Objectives
This research attempts to
i) explore the release-retention and also the mobility of Cd, Cu, Pb
and Sn in soils around dump sites and also to estimate the amount
of these metals that are bound to the various soil constituents.
ii) Simulate the reactivity and mobility of these metals using models
such as MRTM and SOTS Models.
iii) To measure the mobility and relative retention of these metals in
the columns of soil around the dump sites.
iv) To quantity the hysteretic time-dependent sorption and release of
these metals and predict the kinetics of the process of hysteresis in
these soil.
v) To simulate the distribution of these metals with dept of the soil.
vi) To assess the long term effect of waste disposal on the soil
properties.

vii) To create spatial variability maps of these heavy metals using
remote sensing data and GIS tool to delineate area of heavy metal
accumulation.

1.2 Statement of Problems
The mobility of heavy metals in soils is highly dependent on the
physical and chemical soil characteristics as well as heavy metals’
properties. Due to soil heterogeneity and the composition complexity, the
heavy metals reactivity and kinetics vary from one soil to another.
Quantifying the heavy metals kinetics is essential for obtaining a precise
simulation of its mobility in soils. A literature search revealed that heavy
metals transport such as Cd and Cu are commonly described and
predicted based on linear retention where equilibrium adsorption is the
dominant mechanism. Moreover, several studies have been conducted to
investigate Cu mobility and release in acidic as well as alkaline soils
(Sidle et al, 1977; Zhu and Alva, 1993; Chang et al, 2001; Bang and
Hesterberg, 2004; Wang et al, 2009; Sayyad et al, 2010). Only a few
studies, Howevery, have focused on modeling Cu transport in soils,
especially alkaline calcareous soils. Thus, the focus of the current studies
is to describe Cd and Cu transport based on multiple component or
multisite approaches where adsorption is accounted for based on several
nonlinear reactions of the kinetic as well as equilibrium types.

Additionally, literature review regarding Pb reactivity and transport
in soils revealed that numerous studies were carried out for competitive
sorption and transport for Pb with other heavy metals. However, we were
not aware of a study to examine the effect of introducing Cd and Cu
subsequently to Pb pulse into a soil. Also, several studies accounted for
the sorption of inorganic Sn on soil whereas it appears that no studies
have been carried out to explore the influence of Sn on Pb mobility in
soils. In the current research we will use miscible displacement, column
and sequential extraction experiments to assess Pb mobility in soils
around dumpsites and the influence of Cd and Cu on Pb release.
Moreover, batch and column experiments will be carried out to quantity
the sorption-desorption and mobility of single and binary systems of Sn
and Pb in two dump sites.
The behaviour of these chemicals in the environment and the
resulting risk to human health is largely unknown (O’Connor et al, 2008).
For these reasons, we assess the effects of long-term disposal of waste on
soil properties and accumulation of total and available forms of Cd, Cu, Ni, and Pb in soil. Also, the spatial variability maps of those heavy
metals using remote sensing data and GIS to delineate areas of heavy
metals contamination will be provided.

1.3 Rationale of the Study
Use of municipal and industrial wastes from dump sites is a
widespread practice by both urban and rural agriculture. Due to scarcity
of fertilizers and their unaffordability, the use of wastes from dumpsites
fulfills certain socio-economic and environmental goals such as
increasing production or profits and diminishing waste discharge into the
environment. On the other hand, wastes from dump sites are considered a
source of hazardous heavy metals (Singh et al, 2004). Wastes from
dumpsites contain a variety of pollutants including pathogen and heavy
metals which can potentially harm the environment as well as human and
animal health (Qadir et al, 2007). Generally, application of wastes from
dumpsites on farmlands elevates the total and available heavy metals in
soils (Liu et al, 1005). Long term accumulation of bioavailable forms of
heavy metals in soils remain as particularly significant gap in the science
of sustainable agriculture. The behaviour of these chemicals in the
environment and the resulting risk to human health is largely unknown
(O’Connor et al, 2008). In this study, the surface and subsurface soil
sample will be collected from all the selected dumpsites to assess the
bioavailability of heavy metals as a result of their long term
accumulation.