CHAPTER ONE

1.1. Introduction

                
Environmental sedimentology represents a relatively new sub discipline
of the earth sciences and, as such, the boundaries of the field are not clearly
defined. Herein we define environmental sedimentology as ‘the study of the
effects of both man and environmental change upon active surface sedimentary
systems’. Consequently, environmental sedimentology can be regarded as the
study of how both natural and anthropogenic inputs and events modify the production
and accumulation of the physical and biogenic constituents of recent
sedimentary deposits. The field of environmental sedimentology has evolved
gradually over the past two decades, largely owing to an increased recognition of
the influence that anthropogenic activities are exerting upon sediment
production and cycling. Studies in these areas reflect a need to address issues
of sedimentological change driven by environmental or land-use modification or
contamination (Perry and Taylor, 2007).

                The
composition of sediments that accumulate within individual sedimentary
environments is primarily a reflection of three main factors:

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1-       the
sediment source;

2-       the
processes of sediment transport and deposition, which determine whether
sediment is retained or transported through a specific environment.

3-       the chemical
processes operating within the sediment or water column, for example, carbonate
and evaporate precipitation, chemical diagenesis.

               The
sediments in environment are originated from range wide sources are natural and
anthropogenic. In terms of the initial supply of sediment into a sedimentary
system, three basic sediment types can be delineated. These are: (i) detrital
minerals, (ii) biogenic or organic sediments and (iii) anthropogenic particles
and compounds.

1. Detrital minerals

        Detrital
minerals, such as quartz and feldspar, along with heavy minerals, form a
primary component of many terrestrial and marine sediments. These minerals are
initially released by weathering processes and are progressively eroded and
transported into, and through, a range of sedimentary environments. As a
result, initial mineralogical composition of the bedrock often influences the
relative abundance of the individual minerals that are released. Suspended
sediments in the different tributaries have distinct mineralogical and magnetic
signatures that demonstrate variations in the relative importance of different rock
units as sources for fluvial sediment. In reality, these detrital minerals
rarely undergo a simple source to sink transport route, but instead are subject
to numerous phases of weathering, transport, deposition, storage, lithification,
reworking and redeposition (Perry and Taylor, 2007). 

2.
Biogenic and organic sediments

              In
addition to detrital minerals, significant amounts of sediment are derived from
the remains of skeletal carbonate-secreting organisms. These form across a wide
range of marine environments (Schlager 2003), although marked latitudinal
variations occur both in the types and rates of biogenic sediment production
(Lees 1975; Carannante et al. 1988).
Organic inputs, derived from plant material, can also
contribute abundant material to sediment substrates.

3. Anthropogenic particles and compounds

               Increasingly important in many
sedimentary systems are inputs of anthropogenically sourced sediments. these
contain on sediment grains that generated from anthorogenic origin (e.g.
building material, industry) and sedimentary materials that have been heavily
impacted by anthropogenic activity. In this environment, besides that the
extrinsic sources such as soil and vegetation sources, sediment is sourced from
vehicle wear, building material, combustion particles and industrial material. All
of this material has chemical and mineralogical properties distinct from natural sediment grains and, as a consequence,
interacts with the environment in a different manner. Another significant
component of modern sediment, mostly absent from pre-industrial age sediments,
are contaminants. Contaminants in
sediments have different forms including metals, inorganic elements, nutrients,
organic compounds and radionuclides, and the major sources of these
contaminants. Contaminant sources to sediments in the environment may be of
particulate, dissolved or gaseous form, but for most contaminants the
particulate form is dominant (Horowitz, 1991; Perry and Taylor, 2007; Loganathan, 2013).

 

1.2. Sediments in urban environment

            The
urban environment is one that is of increasing importance globally, with
implications for both hydrological and sedimentological systems. Human
activities played the role in the formation and characteristics of urban soils (Yang
and Zhang 2015). The focus on studying urban soils has progressively been
increasing (Burghardt et al. 2015). The reasons being that in the past, only a
small proportion of the population lived in towns and most cities were small in
magnitude. Today, this situation is markedly different. In 2000, about 47% of
the world’s population lived in urban areas, and by 2050, that figure is
projected to be about 66% (Burghardt et al. 2015; Tume et al, 2017). The term urban
sediment is commonly used and is used in a range of different contexts throughout
the literature. In the past urban sediments has been a term commonly
used to refer to sediment accumulation on street surfaces. The study of urban
sediments from the perspective of environmental sedimentology is a young one.
Research into urban particulates originated out of concern for pollution and
human health (Perry and Taylor, 2007).

              Gu
et al, 2016 stated that human activities related to economy and industry are
usually more concentrated in cities, thus resulting that urban areas have also
became the geographic focus of resource consumption and chemical emissions,
leading to problems such as environmental pollution. This is an important issue
in developed and developing countries (Micó et al. 2006; Acosta et al. 2011; Li
et al. 2013). The diversity of urban soils varies from soils that have still
remained unaffected from human impact to soils composed entirely of technogenic
materials that do not occur naturally without human input (Norra, 2014). Similarly,
the levels of contamination found in soils of urban systems vary from almost
undiscernible to extremely high levels. There is also a wide range of both
organic and inorganic contaminants found in urban soils. Currently, the metals
of most concern in urban soils includes lead (Pb), arsenic (As), barium (Ba),
cadmium (Cd), cooper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn) (Levin et
al. 2017). All these potentially toxic elements (PTEs) may originate from many
different sources such as road-deposited sediment (RDS), industrial discharges
(fossil fuel, agrochemical, mining, and smelters), aquatic urban sediments. and
other activities (Tume et al, 2017).

1.2.1. Sediment and contaminant sources

            Sediments within urban environments
originate from a wide range of sources, both natural and anthropogenic, where sediment
sources to subaerial environments (road-deposited sediments) and subaqueous
environments (rivers, canals/docks and lakes).

1.2.1.1. Road-deposited sediment (RDS)              

              Compared with sediment in natural
environments, road-deposited sediment (RDS) has a wide, and diverse, range of
sources. Sources are either intrinsic to the road surface, which are
predominantly anthropogenic in nature, or extrinsic, which are predominantly
naturally derived are shown in Fig (1). Intrinsic sources include vehicle
exhaust emissions, vehicle tyre and body wear, brake-lining material, building
and construction material, road salt, road paint and pedestrian debris.  (Murakami et al. 2005; Perry and Taylor 2007, Hopke
et al. 1980; de Miguel et al. 1997; Charlesworth et al. 2003; Sutherland 2003; Plaza
et al, 2017). Extrinsic sources are soil material, plant and leaf litter, and
atmospheric deposition.

              Pollutant levels in RDS have been studied
in different countries for heavy metals (Fergusson and Ryan 1984; Sutherland
and Tolosa 2000; Ho et al. 2003; Zafra-Mejía et al. 2013), polycyclic aromatic
hydrocarbons (Boonyatumanond et al. 2007; García-Flores et al. 2016), and
nutrients (Vaze and Chiew 2004; Wakida et al. 2014). In urban areas, RDS
contain high concentrations of heavy metals, and also, these areas play an important
role on the accumulation of RDS, especially in areas with commercial and
industrial land use (Zhao et al. 2017). Road-deposited sediments have been
identified as significant contributors to water and air pollution, because the
small particles that are contained in RDS can be re-suspended by the wind or
traffic or transported to water bodies by storm water runoff (Sartor et al.

Fig. (1): Schematic illustration of the sources of
road-deposited sediments (adapted from Taylor, 2007).

1974; Thorpe and Harrison 2008). Harrison et al.
(2012) stated that these latter particles contribute equally to the mass of
RDS. Road-deposited sediments have been identified also as a source of
polycyclic aromatic hydrocarbons (PAH) in storm water (Brown and Peake 2006; Hwang
and Foster 2006). Moreover, Hoffman et al. (1984) calculated that 36%of PAH are
introduced to the environment by urban runoff.

             Heavy
metals and hydrocarbons are considered to be the major contaminants in RDS. Heavy
metal concentration has been widely used as an environmental pollution
indicator since the 1970s because of its effects on human health (Hamilton et
al. 1984; Ubwa et al. 2013). Some authors have reported that one of the main
factors that determine heavy metal concentrations in RDS is land use. Their
findings suggested that areas with residential and industrial land use have
higher concentrations of heavy metals than commercial areas (Sartor et al.
1974; Herngren et al. 2006; Zhu et al. 2008; Duong and Lee 2011). In contrast, some
other studies have reported that RDS from commercial land use had higher
concentrations of heavy metals and have associated these levels to traffic
density (Ellis and Revitt 1982; Viklander 1998). Zafra et al. (2016) identified
three physical factors involved in the accumulation of heavy metals in RDS. These
factors are climatic (rainfall, previous dry period, wind, and atmospheric
deposition), anthropogenic (land use, vehicles, and street cleaning), and
morphometric (particle size, trees, physical characteristics of the basin and
roofs). They also stated that these physical factors can be associated with one
or more processes such as deposition, removal, interception, and suspension.

              Another
main pollutant in RDS is total petroleum hydrocarbons (TPH). They are the
measurable gross quantity of petroleum-based hydrocarbons without identifying
their components individually (ATSDR 1999); it is also a term used to express
the total concentration of nonpolar petroleum hydrocarbons in soil (Saari et
al. 2008). TPH are also known as silica gel-treated n-hexane extractable
material (SGTHEM), which is the remnant compound after the silica gel cleanup
of hexane extracted material. Petroleum hydrocarbons enter the environment by
accidents, leaks, spills, or by-products of domestic, commercial, and
industrial activities. TPH can become a risk to human health and to the
environment (Yuan et al. 2007; Li et al. 2012). They can get into the human
body through breathing, eating, or coming into direct contact with contaminated
soil, water, or food, and can affect human health, depending on the compounds
present in the different fractions of TPH (e.g., toluene, benzene). TPH found
in the soil are able to move to groundwater, where they can evaporate,
dissolve, or move away to another area (McLinn and Rehm 1997; Sharma et al. 2000;
Teng et al. 2013). The presence of TPH in different environmental matrices has been
studied: soils (Adeniyi and Oyedeji 2001; Teng et al. 2013; Plaza et al, 2017), marine sediments (Botello et al.
1991), biota (Fowler et al. 1993), and water (Reddy and Quinn 1999), but only a
few studies have been conducted in RDS.

              Also,
the traffic emissions are significant sources for road deposited sediments
(RDS), where traffic emissions are a significant contributor of diffuse
pollution loads on urban surfaces and subsequent mobilization and transport
towards the water bodies, aquifers and aquatic ecosystems, posing problems for
receiving water quality (Revitt et al. 2014; Shorshani et al. 2015). Part of
air pollutants deposits on surfaces by dry and wet processes, becoming available
to be entrained by the water runoff during rainfall events (Shorshani et al.
2015; Ferreira et al, 2016).

            Traffic
pollutants can have distinct sources. They can be emitted by vehicles engines
through internal combustion, by tyre, clutch and brake wear, fuel evaporation,
and road wear. Exhaust emissions are composed by carbon dioxide (CO2), carbon
monoxide (CO), nitrogen oxides (NOx/NO and NO2), volatile organic compounds
(VOCs), particulate matter (PM), nitrous oxide (N2O), ammonia (NH3), persistent
organic pollutants (POPs) including polycyclic aromatic hydrocarbons (PAHs),
and metals. Nonexhaust emissions are sources of particulate material (PM),
which include inorganic species, trace metals and carbonaceous compounds (Shorshani
et al. 2015). Heavy metal ions are ubiquitous in modern industrialised environments
and a matter of concern due to their toxicity and persistence that make them
particularly hazardous (Burges et al. 2015; Adamcová et al. 2016). Of
particular concern are the processes of remobilisation and movement to the
soils and into the food chain, thereby reaching humans and causing chronic or
acute diseases (Kadi 2009; Brevik and Sauer 2015). Roads can be major sources
of heavy metals (Kadi 2009; Pant and Harrison 2013, Ferreira et al, 2016). Kadi
(2009) states that the trace metal pollution sourced from the roads, where its
nearby agriculture soils, increasing their bio-accessibility. Paved road dust
is the major source of air-born metal to the atmosphere (Kadi 2009; Pant and
Harrison 2013), originated from exhaust pipe emissions, tyre wear, brake wear,
road dust and surface wear (Pant and Harrison 2013).

 Road traffic is
a key contributor of Ba, Zn and Pb (Lin et al, 2005 and Perez et al, 2010)
found Cu, Sb, Ba, Mn and Zn in Barcelona (Spain).

             Tail
pipe emissions are contributing to fine and ultrafine particles through non-exhaust
emissions (Kumar et al. 2013). It is estimated that almost 90%of the total emissions
from road traffic will be originated by non-exhaust sources by the end of this
decade (Rexeis andHausberger 2009). Brake and tyre wear, road surface abrasion,
wear and tear/corrosion of other vehicle components such as the clutch, and
resuspension of road surface dusts are different emissions types for non-exhaust
PM (Pant and Harrison 2013). Non-exhaust emissions are characterized by their
inherent toxicity including the tendency to act as carriers of heavy metals and
carcinogenic components (Hjortenkrans et al. 2007; Johansson et al. 2009). They
have potential acute and chronic human health implications (Crosby et al.
2014). Nonexhaust emissions are typically characterised by trace metals (e.g.
Cu, Zn, Ba, Sb, Mn), known to vary with fleet composition, with heavy duty
vehicles being reported as having higher emissions (Grieshop et al. 2006;
Mancilla and Mendoza 2012). The profile of trace metal concentrations in nonexhaust
PM is found to be unique for every region and varies with traffic volume and
pattern, vehicle fleet characteristics, driving patterns and the climate and
geology setting for the region (Omstedt et al. 2005; Duong and Lee 2011).

               Sources of nonexhaust emissions present a wide
variability given the diversity of tyre and break or road surface types and
composition, many times manufacturer dependent, making it very difficult to
relate source profiles to fleet composition (Pant and Harrison 2013). The relationship
between non-exhaust emissions and traffic characteristics is nonlinear, but
several authors state that a relation with increase vehicle speed (Hussein et
al. 2008; Mathissen et al. 2011). Rainfall rates are affected on the sediments
emissions, were non exhaust emissions are greater than exhaust emissions, these
due to its are low and the wash-off of the road is reduced (Amato et al.
2010b). Emissions from traffic represent a substantial fraction of primary PM
within urban areas (Charron et al. 2007). According to control regulations led
to reduce in exhaust emissions, but nonexhaust emissions from road vehicles are
still persistent. In several European cities, total emissions are an indicator
of exhaust and sources of exhaust, (Querol et al. 2004). Quantification of
nonexhaust particles and attribution to specific sources is difficult. Thorpe
and Harrison (2008) stated that the quantification depends upon the use of
chemical tracers, which are seldom characterized.

1.2.1.2. River, canal, dock and lake sediments

             The
range of sediment sources for rivers and canals is greater than that for RDS,
in that as well as the input of RDS into river sediments, upstream and
downstream input of channel associated material is a major contributor to these
urban aquatic sediments.

               Collins & Walling, 2002 showed
that the sediment in the urban river sections was sourced from channel bank
erosion (18–33%), uncultivated topsoil (4–7%), cultivated topsoil (20–45%), road-deposited
sediment (19–22%) and sewage input (14–18%). The high contribution of urban sources
(up to 40% sewage and RDS) illustrates the marked contrast of urban sediments
to those in non-urbanized catchments. This is in general agreement with Nelson
& Booth (2002), who found that as well as landslides and channel bank erosion,
15% of sediment in an urbanized catchment was from road surface erosion.
Further such studies are required before a full appreciation of the relative
contribution of sediment and contaminant sources to urban rivers can be gained.
As well as contaminant input from road runoff, increased levels of nutrients
(especially phosphorus) and micro-organic pollutants (e.g. pharmaceutical
products) are sourced from sewage treatment works (Owens & Walling 2002;
Warren et al. 2003). Industrial processes are source for metal contaminants to
urban rivers (Walling et al. 2003; Perry and Taylor, 2007).

              Compared
with rivers, which receive sediment from a wide area, canal sediment is
commonly dominated by material that is more locally derived, as a result of the
limited transport of sediment in canals. Industrial sources or sewage and
natural material are eroded from road surfaces and nearby land.  canal and dock systems that have significant
water inputs from rivers, however, can have a significant sediment source from
outside the system. For example, Qu & Kelderman (2001) showed that
sediment, and associated contaminants, in the Delft canals, The Netherlands, have
been derived predominantly from the River Rhine, with the remainder coming from
urban and industrial sources. Urban docks and canals also commonly receive high
levels of organic matter, discharged from combined sewer overflows, and
contaminants derived from boat traffic, for example hydrocarbons and tributyl
tin (e.g. Wetzel & Van Vleet 2003). Within urban lakes, sediment sources
are generally a combination of both eroded soil materials from the surrounding catchment
and anthropogenic material from the urban environment. Atmospheric deposition may
also be an important source of particulates and associated contaminants,
especially for lakes with no direct river input (Charlesworth & Foster
1999). Sediments deposited within lake systems are probably highly catchment
specific and observations made cannot readily be applied to other urban
catchments (Charlesworth & Foster 1999).

               
  Aquatic systems have inputs of
heavy metals, that derived from natural and anthropogenic sources, it is
distributed between different compartments of ecosystems such as water and
sediment. Estimates of the mobility and bioavailability are required to
understand the risk posed to the environment by metals in sediments. River
sediments is a major sink for heavy metals in the aquatic system, the chemical
processes such as precipitation, adsorption, and chelation used to remove the
metals from the water. Sediments have different retention and leaching
capacities for metals owing to variation in properties.  The metals entering or leaving the water
derived from the fine sediments, which it often referred to as suspended
particulate matter (SPM). The particle size affected on The adsorption of
metals from the water phase (Gibbs 1977; Horowitz and Elrick 1987; Ganne et al.
2006; Strom et al. 2011), 

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