Heavy Metal Pollution Of Road Drainage Systems And Remedies

Introduction

This chapter provides an introduction to the heavy metal pollution in road drainage systems while detailing the background of the heavy metal pollution, consequences and effects and sources of the pollution. Meanwhile it describes the path of the pollution and the how does it effect on the society as well as environment.

General

In recent times, urban areas as well as rural areas have been heavily polluted all over the word in compliance with the rapid urbanization. As a part of the urbanization, industries, road networks, sanitary and sewage lines were developed. Besides the urbanization, environmental pollution also has been increasing as mutual occurrences. As a result of environmental pollution many people livening around the urban areas, natural water resources as well as near the roads (Figure 1-1 shows the road runoff) are exposed to an unnatural and unhealthy environment, which may cause serious threat to human health and also environment (Herath et al., 2016). The common pollutants are aromatic compounds, heavy metals, particles of minerals and fibers (Herath et al., 2016).

The term ‘heavy metals’ stands for the any metallic element which have relative density higher than 3.5 to 7 g/cm3 (Ravindra et al., 2014). Heavy metal also caused potential environmental pollution as it may cause health problems and long term or temporary issues, threatened to aquatic environment, long term accumulation in the human body may effect severe diseases such as cancers, organ damages, nervous system damage as well as deaths often occur. At higher dose, heavy metals can cause irreversible brain damages and kidney damages. However, heavy metals are essential for vital processes in humans and many living organisms (Guney el al., 2010). Even though they are pollutants, have great ecological significance due to the toxicity and accumulative behavior (Hoque et al., 2011).

Pollution due to the overland transportation is a common consequence due to the increased commercial and industrial activities in the developing areas (Herath et al., 2016). The road runoff proceeds along with the storm water in contact with surrounded watersheds. In roads, pollutants (Heavy metals) are produced by vehicles (Ni, Cr, Zn, Cu etc.), transported from surrounding soil (pesticides, nitrogen, biodegradable organic matter etc.) as well as wear of the track and security guards (Cu, Cr, Ni, Hydrocarbons etc.). Pollutants are mixed with storm water and flows to the drainages as road runoff and finally reach to the natural water body such as stream, pond or ocean.

Sources of Heavy Metal Pollution

Heavy metals are the most common pollutants found in the sewage water and which would pose toxicity threat to the humans as well as animals even with the low dosage. Cu and Zn are the most common heavy metals generated in order to transportation activities through gasoline, wearing of vehicle parts and oil lubricants (Herath et al., 2016). The problems due to heavy metals are becoming intensive, because those have a higher tendency to be transported along with sediments (dilution with water), are persistent in environment in long term as well as can be accumulated in food chains. Those metals may deposit such a way like dusts and it may expose by breathing as well as storm water will be contaminated and flow through the drainages and finally reach to an ocean or a natural water body. In terms of using old vehicles, poor maintenance of high traffic congestion due to unorganized road networks, poor conditions of roads, construction activities and improper waste disposal methods are common unfriendly environmental practices and it may lead heavy metal discharge to the environment (Hearth et al., 2014).

Vehicular traffic accounts considerable amount of the pollutant discharging towards its usual occurrences nearby the heavily urbanized areas. Heavy metals are releasing from the vehicles in numerous ways as such as; Ni is included in the moving parts of a vehicles, Zn is present in lubricants, tires and galvanized components. In addition to that Cu is a component of break cable devices and Ni is currently added to gasoline and also it may pose pollutant discharges. In order to the construction activities nearby the roads also provides such kind of pollutants as Zn and Cr by paints, building materials as well as vehicles for construction activities. Also, soil of the poorly constructed pavements may mix with dust particles and dilute the metal concentration with water.

There are several situations such as in electro planting, automobile parts as well as Ni-Cd batteries; which includes Ni and its salts. With the road accidents or else vehicle break down incidents cause the releases of Ni as well as Cd to the environment. Moreover, it is widely accepted that Pb particles are discharging to the environment by vehicle emissions through combustion processes (Figure 1-2). These aerosols may exist in the air and with the raining it dilute with storm water and collected to the road drainages as road runoff.

Herath (2014) investigated the heavy metal pollution in road drainage in Colombo, and she specifies that the Cu, Pb and Cr are the most common pollutants included in the road dusts around the industrial zones while Zn and Mn are heavily observed in the commercial areas. However, she further describes the content of Fe amount is very law and due to the corrosion, it may deposit on the roads and the lack of proper cleaning for the roads also poses such contaminations and pollution.

The previous studies regarding with road drainage pollution indicates that, differences due to the locations of anthropogenic activities, traffic characteristics, road condition and texture, location of drainage systems , distance from traffic lane to drainages as well as rain patterns are some of the factors which controls the level of contamination. However, all most all the cases described earlier have high tendency to prone heavy metal pollution towards the transportation services.

Environmental & Health Risks

The heavy metal pollution of road drainage also a part of urban runoff and as a result of this, pollutants may enter to the aquatic and food chains of humans and animals. The road drainages are commonly discharging to the natural water body such as stream, pond or ocean and rarely. It has been sent to the treatment plants in developed countries. The heavy metal pollutants and effect of each are briefly summarized in Table 1-1 as below.

Immunologic

Cd is the most toxic and harmful heavy metal, even in the low concentration it may cause several diseases and unlike other heavy metal it doesn’t essential for any kind of ecological process. Even though it has harmful reports, also using for manufacturing the Ni-Cd batteries. Toxicity of Cd poses lung cancers and increased blood pressure. Cr also heavily toxic element and using in the paper, pulp and rubber applications. High levels of Cr exposure effects liver and kidney damages, impact on central nervous system, skin ulceration as well as for the plants it reduces the photosynthesis.

Cu is using for the electrical wires, pipes and also manufacturing of brass and bronze. However, it is an essential element for human as well as animal bodies and higher doses may result kidney and stomach damages, vomiting and loss of strength. Hg also a highly poisonous compound and which may cause several diseases and most often deaths.

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Ni is frequently using in the moving parts of the vehicles and the vehicle accidents heavily discharge Ni and its compounds to the surrounding environment. The higher dose exposure during long time may damage cells, liver, nervous system as well as heart and also contributes to the cancers, reduction of cell growth and body weight.

However, heavy metal pollution may cause several effects as mentioned earlier and generate environmental problems as listed below.

• Ground water pollution
• Surface water pollution
• Threat for aquatic lives
• Food may contain heavy metals
• Reduces the photosynthesis of plants
• Results acid rains

Through the contaminated road runoff towards the infiltration, ground water table also vulnerable for the pollution. This may lead intensive health problems such as lung and skin cancers, damages for central nervous system, vomiting as well as breathing problems due to the heavy metal pollution of portable water resources. There are standard limitations for the toxic ingredients in the portable water and heavy metal pollution on road drainage results the exceeding limitations.

All most all the drainages are discharging to the natural water bodies and also cause diverse effects on aquatic lives as well as vegetation. Heavy metals are accumulated in the human as well as animal bodies, remain in long term and cause severe consequences. Although, along with the evaporation, heavy metal pollution contributes to the acid rains as well. The water cycle shown in Figure 1-2 shows the better understanding about how does heavy metal pollution causes intensive environmental problems.

Generally, population are primarily expose to the heavy metal pollution via foods such as fish consumption contributes to attain the health problems such as low blood pressure, dental problems as well as neurological damages to adults. So, the fish taken from the highly polluted water bodies should be strictly avoided and the immediate remedies are necessary.

Remedies

This chapter explores the remedies for the heavy metal pollution via road drainage systems. Hence, the previous chapter provides the sources, adverse effects and the risk of contamination towards the environmental and the human well-being. Chapter basically introduce remedies and furthermore details the each remedy.

General

As discussed in the previous chapter, heavy metal pollution through road drainage systems are rapidly increasing and being a threat to the environment as well as living beings. So, the immediate remedies are necessary to take apart to control the issue. Separation of heavy metals in drinking water strongly depends on the modern technology. There are several remediation technologies that have been used to eliminate, control and remove heavy metals from the water such as below.

Local filtration into the road shoulder

Local filtration into the road shoulder is the most common road runoff treatment method affiliate with grass ditches. As soon as the contaminated storm water infiltrate to the road shoulder or embankment, further it may percolate towards the ground water table.

Permeable reactive filter system

In-ground permeable reactive filter system also an environmental friendly heavy metal removal method which comprises with several filter material such as calcite, zeolite, sand and ion filling who basically removes metal contaminants such as Cd, Cu, Pb, Ni, Cr and Zn. It is found that the amount of adsorption as well as removal of heavy metals strongly depend on the type and concentration of metals and also on the filter material. The filter can be provided under the drainages intend to prevent ground water pollution by heavy metals. However, combinations of filter materials can be used to remove heavy metals from the road runoff successfully.

Rhizofiltration

Rhizofiltration also an environmental friendly method with intention to control heavy metal pollution by plants. In this case plants which are grown in the water or water rich material, are directly absorb heavy metals through the roots. Even though, it is an inexpensive, environmental method, the disposal of plant matters as a special waste is required. And also, animal and human access also should be restricted for the plants.

Phytoremediation

Phytoremediation is a method which use plants to uptake contaminants from the contaminated water. It is a more affordable method rather than chemical engineering methods. Since, it is environmental friendly and doesn’t remain concentrated waste water sludge that can harmful for the entire ecosystem.

Coagulation and Flocculation

In this scenario, absorptive materials can be placed in the drainages firmly with intention of absorbing into the solid surfaces (suspended solids) which can settle and also can adsorb to dissolved natural organic matter (DOC) which gets removed in flocculation. Hence, all processes have an appropriate removal efficiency, so the concentration remain after the absorption, also a function of the initial concentration. If there is excessive loading of a metal, one has to look at the efficiency of removal of the current treatment process and then decide if additional treatments, such as KMnO4 or PAC or something else should be added to the drainages as well.

Generally, filter strips are the areas covered by grasses or vegetation with intention of minimizing polluted road runoff as shown in Figure 2-1. The runoff flow over the filter strips is usually a shallow and normally, located in compliance to the sensitive receiving areas. However, this is an environmental friendly, remedial action and road drainage manual of Queensland (2015) specifies following advantages.

• High removal rates of pollutants
• Improved aesthetic view of the area
• Relatively inexpensive approach
• Increase rate of infiltration
• Retention of pollutants near to source

References

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