24 Water quality: Pollution and contamination of surface, ground and coastal water systems, problems of salinity, alkalinity

epgp books

 

 

 

 Introduction

 

Water is used for various kinds of purposes, and the quality is referred with respect to the usage, for example, fishery, agriculture, domestic use, industrial etc. Quality is an important parameter in assessing water’s suitability for a use, for example, whether it is fit for human consumption, or for agriculture. Thus, the sensitivity of a particular crop to the dissolved metals, minerals and toxins in the water sources would determine the selection of crops. Poor water quality not only affects aquatic life, agriculture, and wellbeing of people, but also the surrounding ecosystems.

 

According to the Global International Waters Assessment Report, 2006, the most polluted drainage basins are the Mississippi basin, parts of West Africa, the Atlantic Seaboard basins of Brazil, the Congo and Lake Victoria basins, the Murray- Darling and drainage entering the Great Australian Blight, Baltic and Black Sea drainages. Some islands in the Indian Ocean, Caribbean and Sea of Japan are also impacted.

  1. Water Quality

   Water quality is an important parameter which determines the usability of a water resource for a use, be it agriculture, domestic consumption, drinking and industrial usage especially in food industry. It relates to the specific physical, chemical and biological characteristics of water, and determines the ecological health of the system. The physical characteristics of water quality are primarily temperature, salinity, alkalinity and amount of material suspended in water which influences its turbidity. Chemical characteristics include pH, dissolved oxygen and concentrations of insecticides, herbicides, chemical fertilizers, oils, pesticides and heavy metals. Biological characteristics include phytoplankton and excess growth of algae which smothers corals and leads to poor growth of sea grasses.

 

In India 63,378 rural areas having over 3.6 crore population are living in areas exposed to health hazards related to drinking water quality. The water quality is poor, and has higher amounts of fluoride, arsenic, iron, nitrate or salinity, as stated by Mr. Ram KirpalYadav, Union Minister of Drinking Water and Sanitation on 15th December 2015 in the Parliament. He also stated that 1,318 rural habitations were arsenic-affected, having arsenic levels much higher than the permissible limit in drinking water of 0.05 milligram. He suggested that states install community purification plants, which can provide 8 to 10 litres water per capita per day, especially in the arsenic and fluoride affected areas. Government of India is also planning to provide piped water supply to 90% rural populations by year 2022.

 

In general, water quality is degrading globally, and there are varied responses to it in different parts of the world. This issue needs to be addressed not only in terms of human health but also in terms of ecosystem health.

 

2. Water Pollution

 

Pollution can be broadly defined as the presence or introduction of undesirable substances in environment. The contamination of water, air or land by harmful, poisonous and environmentally degrading substances generates unhealthy and unsuitable conditions for all living beings and serious implications on physical environment. Pollution is mostly caused by human actions, and occasionally by natural causes. A natural cause could be a volcanic eruption, which generates dust, debris, smoke etc. Human causes are manifold – industrial discharges, sewage, chemical spills, agricultural runoff etc. These can contaminate water bodies such as river, ocean, lake, and even underground water channels, rendering them unfit and unsafe for human consumption, detrimental to the aquatic ecosystem and health of organisms as well as toxic for the environment.

 

2.1 Water pollution by natural sources

   Pollution by natural sources is mainly as a result of certain processes of nature which has an impact on the surface, ground and coastal areas (Fig 1). The pollution can be from one source point, like in a volcanic cone eruption, or non-source points, like in landslide prone areas causing damage to soil, gravel and vegetation, from the concrete from buildings destroyed in a landslide.

 

Fig 1: Natural Sources of Water Pollution

    2.2 Water pollution by Human Sources

 

Water pollution can occur from a variety of sources; however, broadly, two terms are used to identify how water gets polluted (Fig 2). Firstly, point sources, in which pollution is from discrete locations. It can be a single sewer pipe discharge or a factory or an industrial unit or a runoff from a single farm. For example, the oil spill from Bharat Petroleum in 2010 is point source pollution – the single point leakage of massive amount of oil into a water body. The location of pollution and its sources are identifiable and can be legally controlled through legislations.

 

Secondly, non-point source pollution, in which there several points of contamination over a large area, and therefore, no single source or point generating pollution. The water bodies like river, lake, pond or sea or ocean are contaminated by multiple sources like urban discharges, agricultural runoff (inthe form of pesticides, fertilizers etc.), oil spills and industrial untreated discharges. The non point pollutants pollute the water sources through drainage, land runoff, flood, precipitation, seepage or hydrological modifications, atmospheric deposition etc. Since the source of pollutants is not easy to identify, it makes it more difficult to regulate. For example, the Yamuna, the Ganga and the Mississippi rivers are water bodies where there is evident risk from non-point sources of pollution because these river systems are very large and exposed to a variety of pollution sources. Water bodies in Delhi are severely polluted by various kinds pollution few glimpse are shown (plate 1, plate 2, plate 3).

Fig 2: Human Sources of Water Pollution

 

 

2.3 Pollutants in the water

 

The pollutants in water can be categorized into inorganic, organic, biological and natural pollutants on the basis of their nature (Fig 3).

 

Organic Pollutants include fats and grease, and oxygen-demanding substances, which are generated as waste from food proceeding units. Chloroform which is used as a disinfectant in drinking water also causes disinfection by-products. Chlorinated solvents are denser than water, and may sink to the bottom of reservoirs, as they do not mix well with water. Industrial solvents improperly stored can leak into the water sources, and can include volatile organic compounds. Herbicides, pesticides and insecticides have large composition of organ halides and many other chemical compounds. Debris from forest cutting sites, like timber, bushes, leaves and branches etc. can cause pollution in the water channels. Perchlorate and trichloroethylene are also industrial pollutants. The United Nations Programme Governing Council, 1995 has identified 12 persistent organic pollutants (POP). Also referred to as the ‘dirty dozen’, they include DDT, aldrin, endrin, benzenehexachloride, and carcinogenic polycyclic aromatic hydrocarbons (PAH). POPs are resistant to environmental degradation, and capable of long range migration also biomagnifying food chains and impacting environment.

 

Fig 3 : Classification of various types and sub types of Water Pollutants

Inorganic pollutants include copper, zinc, lead, nitrate, nitrite, cadmium, phosphorous, ammonia and phosphate, which have ions traces in the environment. These pollutants enter water sources through industrial discharges from power plants in the form of sulphur dioxide, nitrates and phosphates from fertilizers, runoff from residential and commercial uses, ammonia from the food processing units, discharges from mining sites, and emissions from motor vehicles.

 

Biological pollutants include viruses, house dust, pollen, bacteria, etc. A biological pollutant can originate from various sources such as coliform bacteria from plants and soils or from the warm blooded animals including humans, pollens from plants, viruses from humans and animals etc.

 

Radioactive pollutants are generated by nuclear reactors, mining, radioactive geological formations, industrial waste sites, medical treatment and diagnosis, weapons etc. Some of these also generate tremendous amount of heat. These kinds of pollutants in water cause various kinds of cancer and damage tissues in humans and other organisms that consume the contaminated water.

 

 3. Surface Water Pollution

 

Surface water consists of water channels above the ground such as rivers, lakes and streams. The surface water becomes polluted mainly by rainwater runoff which carries various kinds of pollutants along with it into aquatic systems, such as salts, chemicals from industries, and fertilizers and nutrients from agricultural farms and gardens (‘nutrient pollution’). This causes overproduction of algae, which creates layers over the water surface, thereby hindering sunlight penetration to underwater plants and aquatic organisms. This leads to lower levels of oxygen generation, causing problems to oxygen breathing organisms like fishes. The sewage leaks, and runoff from slaughter houses and animal farms, and factory discharges cause pathogens and waterborne diseases. The bacteria and viruses that pollute the surface water channels cause dangerous human health problems like hepatitis and typhoid. The pesticides, lead, arsenic and mercury from mining sites, synthetic chemicals from motor vehicles are also very dangerous for the environment, also deteriorating the health of organisms that inhabit them.

 

With the growth in population in many parts of the world,especiallyin the developing countries, and improvement in the standard of living, there is increase in the demand for freshwater. On the other hand, pollution from agricultural, industrial and urban areas is also increasing, rendering water resources not suitable for consumption. In certain cases, the rivers have become biologically dead and poisonous, with ammonia levels soaring, making them unsuitable for drinking. It is estimated that there are 5 million deaths each year in the developing countries due to water related diseases, which could be prevented by adequate supplies of clean water.

 

Surface water bodies, especially rivers, need to be analyzed in totality, including the river basin or the catchment area. They are complex ecosystems, with millions of pollution causing sources around them. The awareness and need to reduce pollution is gaining importance, but major improvements will require long durations, in somecases decades, in the large river basins.

 

3.1 Main causes of surface water pollutants

 

The major pollutants in the surface water systems are heavy metals toxins, persistent organics and organic chemicals generated as industrial waste. Human waste through sewage networks, or directly, causes occurrence of pathogens in the form of bacteria and viruses. Agricultural generated pollutants in the form of chemical fertilizers, pesticides, insecticides etc. might seep into water channels through runoff. Run offs into the river systems and surface water bodies can also cause pollutants such as debris.

 

3.2 Problem and solution of surface water pollution

 

Almost all the developing countries face water quality problems in the major rivers and surface water bodies. The northern rivers of India, in the Ganga-Yamunabasin, face serious pollution related issues. In China, the river Huai is highly polluted due to uncontrolled industrialization. Smaller rivulets or tributaries flowing through the urban areas are the main source of water for those urban areas, but have also become urban drains or ‘rubbish tips’. Many counties are trying to address the surface water pollution by learning from the experiences of rehabilitation of rivers like Thames and Rhine, which have been resuscitated with decades of effort and investment. India launched the Ganga Action Plan in the 1980s to clean up Ganga, and reduce the pollution level. Despite millions of rupees having been spent on it, the demonstrable effect is abysmal. China has significantly reduced the pollution levels of Huangpu River in the centre of Shanghai by spending billions of dollars for cleaning and relocation, or closure, of many polluting industries, in last two decades.

 

4 Ground water pollution

 

Ground water is estimated to serve 20% of global population. The ground water aquifers are slower to show the impact of pollution, but the contamination is far difficult to solve, as the source is beneath the surface and so difficult to control or monitor the pollution levels. It was earlier thought that the layers of soil and sediments would filter all the impurities before the water reaches the aquifers, but in the 1970s it was realized that the impurities still seep into the aquifers and thereby contaminate the ground water. Once the underground water is contaminated, it becomes unfit for consumption and would require decades to normalize. There is no quick and inexpensive method to clean ground water channels. The contamination can occur naturally by metallic or mineral deposits in soil or rock, for example, toxic metal arsenic found as sediment rock in many parts of United States can cause excess levels of arsenic concentrations in the drinking water exceeding the safe limit. Coastal areas have the problem of saltwater intrusion wherever the rate of groundwater pumping is high, and sea water invades the freshwater aquifers.

 

4.1 Types of ground water contamination by humans

 

Human activities generate two categories of ground water pollution: point and non-point source pollution. The point source pollution relates to contamination from a single source, such as a spill from a tank or leaking oil tankers, gasoline storage tanks, disposal facility or industrial waste disposal sites, landfills or dumps. The non-point sources of pollution are spread out and impacts large areas. Excessive use of chemicals in the form of herbicides, fertilizers and pesticides over large agricultural areas eventually reach the underlying aquifers. The impact is higher in regions where the aquifers are shallow and the surface is covered by very permeable materials, thereby speeding the penetration into the ground aquifers. The surfaces covered by clay are low on permeability which can help in reduced penetration. Runoff from urban and industrial areas also causes non point sources of pollution. The impact of non point sources of pollution effects water quality over a large area as compared to point source pollution. The damage to septic pipelines can cause spread of contamination over a large area. In industrialized areas there is high risk of contamination by petroleum and chemical products. Chlorinated solvents in the form of dry-cleaning fluid known as perchloroethylene also pollute ground water (Fig 4).

 

Fig 4 : Point and non-point sources of ground water

    Point Sources of Ground water

 

Leaky tanks or pipelines containing petroleum products Asphalt production and equipment cleaning sites

 

Sludge disposal areas at petroleum refineries Land spreading of sewage or sewage sludge Graveyards

 

Road salt storage areas

 

Wells for disposal of liquid wastes

 

Runoff of salt and other chemicals from roads and highways Spills related to highway or railway accidents

 

Coal tar at old coal gasification sites On-site septic systems

 

Source: Adapted from: Cherry, John A. “Groundwater Occurrence and Contamination in Canada.” In M.C. Healey and R.R. Wallace, Canadian Aquatic Resources, eds., Canadian Bulletin of Fisheries and Aquatic Sciences 215: 395. Department of Fisheries and Oceans: Ottawa, 1987.

 

4.2 Methods of cleaning ground water

 

Containment should be done to prevent contaminated water from a polluted aquifer to migrate from the source. This can be done physically, by using a physical barrier of cement, clay or steel underground, or chemically, by detoxifying or immobilizing the contaminant by using reactive substances etc.

 

Removal of the contaminants from the aquifer can also be attempted, such as metals, pesticides, organic chemicals. Salt intrusion in coastal areas can be reduced by appropriate well field design, and also by drilling relief wells to keep salt water away from fresh water.

 

Build in capacities to detoxify or immobilize the pollutants while they are still in the aquifer, and then removal from the aquifer by ground extraction wells. This is done by pumping and treating – it takes a long time to cleanup, but can successfully remove most of the contamination from the aquifer.

 

Treating the ground water at the point of its use. Depending upon the type of contamination some ground waters cannot attain safe quality. In case of large water providers, evaporation towers called air strippers or special filters need to be installed, while the personal well owners can install reverse osmosis filters or whole house carbon filters.

 

Totally abandoning the use of the contaminated aquifer and finding alternative source of water.

  5. Coastal water systems

 

Coastal water systems have their own set of specific issues, such as, alternative water supply projects like aquifer storage and recovery, desalination and reclaimed water use, which are being explored in the coastal areas. There are various types of coastal pollution and their impacts (Fig 5 and 6).

 

Fig 5 : Types of Coastal Pollution

 

Fig 6: Systematic preview of coastal water pollution and their impact

5.1 Consequences of coastal water pollution

 

Contamination causes concentration of pollutants which is called bio-accumulation or bio-magnification (Fig 7). The planktons have lower concentration of pollutants but as we go up in the food chain, the concentration of pollutants increases. For example, tuna fish has greatest concentration of pollutants.

 

Fig 7 : Impact of Bio magnification on food chain

 

    ppt= parts per trillion (mercury concentration)

 

Impacts from of South coastal Florida pollution Restoration Science Forum  ‘a case study of south Florida region’

 

a) Coastal pollution may drastically reduce the tourist business in the region

 

b) A species from outside the region may become common, causing imbalance in the local aquatic ecosystem, leading to health problems, change in fisheries pattern and interfering with tourism.

 

c) Marine life and birds are caught in wastes like plastic bags and rings, oil spills etc.

 

d) Large quantities of carbon and nutrient leads to plankton blooms. Once the plants die, they sink to the bottom, disintegrate, decay and release carbon dioxide, thereby reducing the amount of oxygen in deeper waters.

 

Coastal pollution can have non-point pollution characteristics, such as pollution being transported into coastal environments via rivers or streams, ground water, the atmosphere, combined sewage flows, flood channels, storm water runoff or leaking septic tank etc (Fig 8).

Fig 8: Non point source of coastal pollution types and factors

   6. Salinity

 

Salinity is a measure of the presence or concentration of total dissolved salt in water or soil, mainly sodium chloride (common salt).Soil salinity is the salt content in the soil, and over time there is process of increasing salt, and this is called salinization. This can occur due gradual withdrawal of an ocean, or mineral and chemical weathering of soils. Water salinity accounts for all the salts dissolved in water. It is measured in terms of parts per thousand (ppt). The average river water salinity is 0.5 ppt or less whereas the ocean salinity is 35 ppt.

 

Human activities are contributing to salinization of water. The disposal of liquid waste or saline wastes into well or basins, or the solid waste that contains soluble salts and are present in landfills sites. These can leach by rainfall into the underground water or buried beneath the water table. During extraction of ground water, it causes intrusion of saline water, as the extraction causes disruption of interface of saline/ fresh water. The use of saline surface water for irrigation can increase salinity of underground water, if the water returns to underground aquifers as recharge.

 

Major causes and activities that increases salinity levels of surface water are as follows-

 

The salinity is affected by changes in diversions, and return flow along with losses and gains from ground water in neighbouring strata. In highly irrigated areas there are greater chances of increasing salinity load of streams and rivers. The changes in management of vegetation and soil in non irrigated areas can cause increase recharge of underground water and discharge of salts in stream and rivers. Construction of canals and reservoirs can cause leaching of salts downstream, and the saline groundwater gets displaced from underlying strata into streams and rivers.

   Salinity in arid and semi arid areas is major problem, and advancement of deserts due salinization is threatening agriculture globally. Secondary salinization in arid and semi arid areas is getting widespread due to over use of irrigation schemes. It is estimated that 20% of all irrigated areas are salt affected. Agricultural crops are severely affected by higher concentration of salts in soil and water as they are sensitive to salinity. There are serious impacts of salinity on water supplies and soil structure. In most areas salinity is a outcome of faulty agricultural practices like over irrigation, water logging, over use of chemicals in form of pesticides, fertilizers etc.

 

6.1 Problems of salinity

Salinity reduces the soils capability to percolate water into sub surface, which can cause flooding during heavy rains.

 

Salinity is a major threat to biodiversity, in the form of loss of habitat both in water and on land. Salts alter the in-stream bio strata and also change the health of estuaries and streams.

 

Salinity problem is higher in dry arid environments, where the evaporation rates are generally very high, causing salts to leach on surface. Poor quality irrigation water with high concentration of salts can have a greater impact.

 

Salinity increases the maintenance and repair costs of public and private goods like infrastructure; roads, bridges, sewage pipes; housing and industry.

 

Salinity directly affects people in the form of increasing costs to rehabilitate saline farms, declining rural population, stress related to lower productivity etc.

 

Salinity indirectly affects the human by reducing the quality of natural environment; for example, there is decrease in wildlife in the salinized natural wetlands.

 

6.2 Impacts of salinity in water

 

Salinity in ground and surface water has significant effects on the surrounding environment, and the health and well-being of ecosystems. Saline soils generally become bare and compact, creating conditions leading to gully or sheet erosion. This generates huge sediment and salt loads in water courses, thereby degrading water quality downstream. High concentration of salts in water is quite unpalatable for humans and livestock. The toxic ions, particularly manganese and sulphate ions in water can cause gastro-intestinal irritation in cattle, and impact their reproduction and contaminate milk products. The aquatic ecosystems get significantly impacted by increasing salt content in water. Saline water corrodes the materials used in construction of bridges, foundation of buildings; sewerage pipes etc., and can sometimes disrupt the local water supply. It impacts the productivity of the rural regions. In urban areas, like Wagga-Wagga in the outer suburbs of Sydney, saline soil and water is causing rusting in motor vehicles and decaying building foundations. The salty water is damaging the hot water systems, septic tanks, household appliances etc., causing huge loss.

 

The factors affecting saline seeps can occur due to excess water or soil characteristics or both are shown in Fig 10. In dryland areas saline seepage leads to accumulation of salt in seepage spots at lower points, or side slopes in the landscape developed, in case water infiltrates into soil having impermeable layers and moves down slope. The water at lower elevations seeps laterally at the soil surface, and as water evaporates the salts are left behind. If water is in excess of the retention capacity of the root zone soil, it percolates greater than the root zone, and reaches the ground water thereby increasing the flow to the discharge area. When the groundwater is travelling to the discharge areas the salts from the soil also travels with it. In the discharge zone the groundwater rises to the soil and water evaporates the surface forming a seep (Fig 10 and 11).

 

Fig 11: Factors influencing formation of saline seeps

 

 

Fig 10: Diagram of a recharge and seepage in saline areas within healthy environment

Impermeable layer

Fig 11: Step by step diagram of a recharge and a seepage area (zone of salt accumulation)

 

   7 Alkalinity

 

Water alkalinity can be defined as its capacity to neutralize acid content. Hydroxides, carbonates and bicarbonates are alkali substances found in water. One or more number of ions is present in water thereby making the water body alkaline. Some amounts of hydroxides are naturally present in water; there levels can rise due to some treatments in domestic supplied water sources. Bicarbonates are the most prevalent source of alkalinity in water. Bicarbonate ions if in small amounts will not show alkaline conditions only can be noticed if in large quantities. Some amounts of carbonates are naturally present in water. Increase in levels of carbonates due to addition of lime soda which is used to soften the water. Silicates and phosphates are seldom found in natural water supplies. But they are used in various water treatment processes. To balance the corrosive effects of acidity in most water supplies moderate concentrations of alkalinity is desirable but only in moderate quantities as excess will cause number of problems. Alkalinity can be easily detected even if small quantities of carbonate and hydroxide ions presence.

 

Water severely alkaline has an objectionable ‘soda’ taste. Calcium, magnesium, potassium and sodium ions needed to be cautioned.

 

The pH (potential of Hydrogen) value signifies the measure of alkalinity or acidity of water soluble substances (Fig 12). The range is 1-14 where the middle value is 7 indicates neutrality. The values above 7 indicate increasing concentration of alkalinity where 14pH signifies most alkaline. The values below 7 represent increasing levels of acidity where 1 value is most acidic. The scale is logarithmic scale by factor of 10 in two adjacent values which decrease or increase. The capacity of water to resist change in pH values is called “buffering capacity” where alkalinity suggests the waters capability to neutralize acid.

 

Fig 12: pH scale with impact

    Problems related to alkalinity in water

 

a) Alkalinity helps to create buffer against increasing components of acidic materials in water to protect aquatic life and fishes. Loss or temporary loss of buffering capacity will lead to drop in pH levels to harmful levels for life in water. Most plants and animals in aquatic environment require a specific Ph value for their survival and slight change can lead to mass deaths. The pH ranges between 4-10 levels any range above or lower will kill most of the fish in waters. The living things are very sensitive to changes in pH values.

 

b) The Michigan State University research identifies to high pH value more than 6.5 increases the risk of micronutrient deficiencies and less than 5.3 pH results in magnesium or calcium or manganese toxicity.

 

c) An ecological study in Netherlands had found out that influx of alkalinity has caused demise of native plant called Stratiotes aloides.

 

d) Ohio State University extension service that alkaline water can impact the plant’s capability to obtain nutrients from the soil and also alters the pH levels of the soil over time.

 

e) Acidity is dangerous for human bodies and increasing levels of alkalinity is equally dangerous because both cause nutritional imbalance. Few scientists are of the view that normal cells die excessively in alkaline environments. In normal course the alkaline water mixes with the gastric acid and neutralize in human body. If there are increasing levels of alkalinity in stomach they will further dilute the levels of gastric acid which is helpful in digestion and also kills body parasites. This situation can lead to mal absorption nutrients and can cause deficiencies.

 

you can view video on Water quality: Pollution and contamination of surface, ground and coastal water systems, problems of salinity, alkalinity

 

References