Water Pollution, Types and Impact

What is Water Pollution?

Water pollution is defined as alteration in Physical, Chemical and biological characteristics of water which may cause harmful effects on humans and aquatic biota.

Properties Of Water

• It is an excellent solvent which assists in transportation of nutrients and waste products, making biological processes possible in an aqueous medium.

• It has the highest dielectric constant among the common liquids, which causes the high solubility of ionic substances and their ionization in solution.

• It is transparent to visible and longer-wavelength fraction of UV light , allowing light required for photo synthesis to reach considerable depths in bodies of water

• It has a maximum density as a liquid at 4 ^oC which restricts vertical circulation in stratified bodies of water.

• It has higher heat of evaporation than any other material which determines transfer of heat and water molecules between the atmosphere and bodies of water.

• It has higher heat capacity than any other liquid except ammonia which helps in stabilization of temperature of organism and geographical region.

What are the Main Causes of Water Pollution?

Water pollution is mainly caused by:

• Natural process in which the decomposed vegetable, animal and weathered products are brought into main water resourses.

•Anthropogenic Process such as industrial, agricultural, urban, domestic, radioactive, mining sources, use of pesticides and fertilizers by man etc.

Major Water Pollutants and their Significance

Class of pollutant	Significance
Trace Elements	Health, aquatic biota, toxicity
Heavy metals	Health, aquatic biota, toxicity
Organically-bound metals	Metal transport
Radionuclides	Toxicity
Inorganic pollutants	Toxicity, aquatic biota
Asbestos	Human health
Algal nutrients	Eutrophication
Acidity, alkalinity, salinity (in excess)	Water quality, aquatic life
Trace organic pollutants	Toxicity
Polychlorinated biphenyls	Possible biological effects
Pesticides	Toxicity, aquatic biota, wildlife
Petroleum wastes	Effect on wildlife, esthetics
Sewage, human and animal wastes	Water quality, oxygen levels
Biochemical oxygen demand	Water quality, oxygen levels
Pathogens	Health effects
Detergents	Eutrophication, wildlife, esthetics
Chemical carcinogens	Incidence of cancer
Sediments	Water quality, aquatic biota, wildlife
Taste, odor, and color	Esthetics

Classification of Water Pollutants

The various types of water pollutants can be broadly classified into the following five major categories-

1.Inorganic Pollutants

2.Organic Pollutants

3.Suspended Solids and Sediments

4.Radioactive Materials

5.Heat

Inorganic Pollutants

Trace elements

Metalloids

Inorganic compounds

Cyanides

Sulphates

Nitrates

Mineral acids

Inorganic salts

Organometallic compounds and complexes

The most toxic among the trace elements are the heavy metals, such as  Hg, Cd, Pb.

The  heavy metals have great affinity for sulphur and attack the –S-H bonds in enzymes, thereby immobilizing the latter. Protein carboxylic acid groups (-COOH) and amino-groups (-NH₂) may also be attacked by the heavy metal ions. The heavy metals that may be bound to the cell membranes interfere with the transport phenomena across the cell. The heavy metals also tend to precipitate bicompounds or catalyse their  decomposition.

Water pollution by heavy metals occurs mostly due to street dust, domestic sewage and industrial effuents.

Cadmium

Cadmium is generated in waste streams from pigment works, textiles, electroplating chemical plants etc. Ø Because of its chemical similarity to zinc, cadmium replace zinc in some enzymes, thus altering the stereo structure of the enzyme and impairing its catalytic activity. Ø Cadmium causes acute poisoning in humans resulting in kidney damage, destruction of testicular tissue and distruction of red blood cells.

Lead

The sources for lead pollution are industry and mining in which lead is present in +2 oxidation state. ØFood and direct ingestion of the dust account for most of the average lead intake by humans. Ø Acute lead poisoning in human causes malfunctioning of kidneys, reproductive system, liver, and the brain and central nervous systems.

Chromium

Cr(III) has low toxicity, but Cr(VI)  is both toxic and carcinogenic to humans. ØHexavalent is present in waste waters of plating operations, aluminium anodising, paint and dye operations, and leather industries. ØTrivalent chromium is present in waste waters from textile dyeing, the ceramic and glass industry, and photography. As the effluent flows downstream, the dissolved oxygen can oxidise Cr³⁺ to Cr₂O₇^2-

Since Cr(III) is poorly absorbed by any route, the toxicity of chromium is mainly attributable to the Cr(VI) form. It can be absorbed by the lung and gastrointestinal tract, and even to a certain extent by intact skin.

The reduction of Cr(VI) is considered to serve as a detoxification process when it occurs at a distance from the target site for toxic or genotoxic effect while reduction of Cr(VI) may serve to activate chromium toxicity if it takes place in or near the cell nucleus of target organs [Dayan and Paine 2001]. If Cr(VI) is reduced to Cr(III) extracellularly, this form of the metal is not readily transported into cells and so toxicity is not observed. The balance that exists between extracellular Cr(VI) and intracellular Cr(III) is what ultimately dictates the amounts and rates at which Cr(VI) can enter cells and impart its toxic effects [Cohen, Kargacin et al. 1993].

Cr(VI) enters many types of cells and under physiological conditions can be reduced by hydrogen peroxide (H₂O₂), glutathione (GSH) reductase, ascorbic acid, and GSH to produce reactive intermediates, including Cr(V), Cr(IV), thiylradicals, hydroxyl radicals, and ultimately, Cr(III). Any of these species could attack DNA, proteins, and membrane lipids, thereby disrupting cellular integrity and functions.

Mercury

Mercury is discharged into natural waterways from manufacture of paint, paper, chlorine and caustic soda, fertilisers and pesticides.  The toxicological effects of mercury are neurological damage, chromosome breakage; and birth defects. ØThe toxicity of mercury was tragically illustrated in the Minamata bay area of Japan during the period 1953-1960.

Unexpectedly high concentrations of mercury were found in water and fish tissues in the US and Canada around 1970. They were attributed to the formation of soluble monomethyl mercury ion CH₃Hg⁺, and volatile dimethyl mercury, (CH₃)₂Hg by anaerobic bacteria in sediments. Mercury from these compounds becomes concentrated in fish lipid tissue and the concentration factor from water to fish may exceed 10³. The methylating agent by which inorganic mercury is converted to methyl mercury compound is methylcobal amine, a vitamin B12 analog.

Organic mercury compounds, specifically methylmercury, are concentrated in the food chain. Fish from contaminated waters are the most common culprits. Industrial mercury pollution is often in the inorganic form, but aquatic organisms and vegetation in waterways such as rivers, lakes, and bays convert it to deadly methylmercury. Fish eat contaminated vegetation, and the mercury becomes biomagnified in the fish. Fish protein binds more than 90% of the consumed methylmercury so tightly that even the most vigorous cooking methods (eg, deep-frying, boiling, baking, pan-frying) cannot remove it.

For centuries, mercury was an essential part of many different medicines, such as diuretics, antibacterial agents, antiseptics, and laxatives. In the late 18th century, antisyphilitic agents contained mercury.

Minamata disease is an example of organic toxicity. In Minamata Bay, a factory discharged inorganic mercury into the water. The mercury was methylated by bacteria and subsequently ingested by fish. Local villagers ate the fish and began to exhibit signs of neurologic damage, such as visual loss, extremity numbness, hearing loss, and ataxia. Babies exposed to the methylmercury in utero were the most severely affected. Furthermore, because mercury was also discovered in the breast milk of the mothers, the babies\’ exposure continued after birth.

Mercury in any form is poisonous, with mercury toxicity most commonly affecting the neurologic, gastrointestinal and renal organ systems. Poisoning can result from mercury vapor inhalation, mercury ingestion, mercury injection, and absorption of mercury through the skin.

Mercury has 3 forms:

(1) elemental mercury,

(2) inorganic salts, and

(3) organic compounds.

Elemental liquid mercury as the pure metal is non toxic except by inhalation which can cause severe neurological symptoms but is generally non lethal.

Inorganic, ionic forms of mercury tend to cause gastrointestinal damage but don\’t cross the blood brain barrier.

Organic mercury compounds are quite toxic as they tend to diffuse through the body and are easily absorbed through the skin. The most deadly form of mercury is methylmercury. Only 2-10% of the ingested mercury is absorbed from the gut, and ingested elemental mercury is not absorbed at all; however, 90% of any methylmercury ingested is absorbed into the bloodstream from the gastrointestinal tract. Methyl mercury and dimethyl mercury are the most dangerous as they form conjugates with cysteine that mimic another amino acid methionine, which is then actively distributed through the body and into the brain.

Ø Among the metalloids  As, Sb and Se are water pollutants but As is the most significant.

Ø These compounds undergo putrefaction by bacterial action to release sulphur and phosphorous compounds like H₂S and SO₂ which in turn cause putrid and musty smell in water.

Ø  As(III) (arsenite, AsO₃^{3 –}) is more toxic than As(V) (arsenate, AsO₄^3-), probably because it binds more readily to sulfhydryl groups on proteins. Toxicity of As(V) probably results from its reduction to As(III) in the body.

Cyanide:

Cyanide is a deadly poisonous substance, that exists in water as HCN; It is a very weak acid. Cyanide ion forms stable complexes with metal ions and these complexes are relatively less toxic. The cyanide ion has a strong affinity for many metal ions forming relatively less toxic complexes. For example with iron (II) it forms less toxic [Fe (CN)₆ ] ^{4 –} where as volatile HCN is toxic. Especially metal cleaning and electroplating industry use large quantities of cyanides. The presence of cyanide in water is indicative of a serious pollution problem. When a living organism is exposed to water contaminated by cyanide ions (CN⁻)  in water causes cyanide poisoning. Common poisonous cyanide compounds include hydrogen cyanide gas and the crystalline solids potassium cyanide and sodium cyanide.

Ammonia :

Ammonia is formed during the microbial degradation of decaying biomass and organic matter in soil and water. Nitrogenous compounds like proteins are ammonified to release ammonia into the surroundings. Sometimes it is added to drinking water during chlorination where it reacts to provide residual disinfectant chlorine.

Sulphite:

Some industrial wastes contain sulphite ions where sodium sulphite is added to boiler feed waters as an oxygen scavenger:

2SO₃^{2-  +}  O^2-                                   2SO₄^2-

Sulphate:

Sulfates (SO₄^2-)can be naturally occurring or the result of municipal or industrial discharges. When naturally occurring, they are often the result of the breakdown of leaves that fall into a stream, of water passing through rock or soil containing gypsum and other common minerals, or of atmospheric deposition. Point sources include sewage treatment plants and industrial discharges such as tanneries, pulp mills, and textile mills. Runoff from fertilized agricultural lands also contributes sulfates to water bodies. Health concerns regarding sulfate in drinking water have been raised because of reports that diarrhea may be associated with the ingestion of water containing high levels of sulfate. Recommended limits for water used as a Domestic Water Supply are below 250 mg/L.

 Hydrogen sulfide:

The anaerobic decay of organic matter containing sulphur leads to the production of H₂S. Anaerobic reduction of sulphate in water by microorganisms is also a natural source for hydrogen sulphide. H₂S is evolved as a gaseous pollutant from geothermal waters (ground water that is heated by the earth’s energy). Wastes from chemical plants, paper mills, textile mills, and tanneries may also contain H₂S. It is a weak diprotic acid and S^-2 is not present in normal natural waters. The sulphide ion has tremendous affinity for many heavy metals and precipitation of metallic sulphides often accompanies production of H₂S. Ø

Nitrite:

Nitrite seldom appears in concentrations greater than 1mg l^-1, even in waste treatment plant effluents. Its concentration in surface and ground-waters is normally much below 0.1 mg l^-1. Nitrite is added to some industrial process water to inhibit corrosion; it is rarely found in drinking water at levels over 0.1 mg l^-1.

Organically Bound metals & Metalloids

In aquatic system organometallic compounds are classified  as-

1. Compounds in which the organic group is an alkyl group such as ethyl in tetra-ethyl lead, Pb(C2H5)4

2. Canbonyls

3. Pi electron donor

There are two major types of metal-organic interactions to be considered in an aquatic system.

Ø Complexation, usually chelation when organic ligands are involved

Ø Organometallic compounds, contain metals bound to organic entities

A large number of compounds exist that have at least one bond between the

metal and a C atom on an organic group, as well as other covalent or ionic bonds between the metal and atoms other than carbon. Examples are monomethylmercury chloride, CH₃HgCl, (CH₃Hg+ ion is ionically bonded to the chloride anion.) and  phenyldichloroarsine, C₆H₅AsCl₂

it may be noted that metalorganic interactions may involve organic species of both pollutant (such as EDTA) and natural (such as fulvic acids) origin. These interactions are influenced by, and sometimes play a role in, redox equilibria; formation and dissolution of precipitates; colloid formation and stability; acid-base reactions; and microorganism-mediated reactions in water. Metal-organic interactions may increase or decrease the toxicity of metals in aquatic ecosystems, and they have a strong influence on the growth of algae in water.

Acid Mine drainage

Coal mines, especially those that have been abandoned, are known to release substantial quantities of sulphuric acid and iron hydroxide into local streams. The first step in the process is the oxidation of pyrite (FeS₂ ), which is common in underground coal streams.

This step is mediated under aerobic conditions by the bacterium thiobacillus ferro oxidans, which oxidises FeS₂ as an energy source much the same way that other aerobic bacteria oxidise organic carbon (CH₂O) in respiration reactions. The oxidation step occurs spontaneously at ambient temperatures once iron sulphide , which is stable in the absence of air is exposed to atmosphere. In the second step, the ferrous iron (Fe²⁺) combines with oxygen and water in the overall reactions.

Thus one mole of pyrite produces 2 moles of sulphuric acid and one mole of ferric hydroxide , which is removed from the solution as a brown precipitate. The pH of the streams receiving this drainage can be as low as 3.0

Environmental chemists have a tough challenge in the prevention of water pollution from acid mines. Even though at the first instance, it may appear that this problem can be remedied by using carbonate rocks to neutralise the acid as per the following equation.

CaCO₃ + 2H⁺ +SO²₄ ⁻ → Ca²⁺ + SO²₄⁻ +H₂O +CO₂

this reaction is inhibited after sometime since the formed ferric hydroxide form an impermeable layer with the calcium carbonate particles

Accumulation of Salts in water

Water naturally accumulates a variety of dissolved solids, or salts as it passes through the soils and rocks on its way to the sea. A more commonly used measure of salinity is to determine the concentration of total dissolved solids in the water sample. All naturally occurring water has some amount of salt in it. While human activities may increase salinity by adding salts to a given volume of water, it is more often the opposite process, the removal of fresh water by evaporation, that causes salinity problems. When water evaporates, the salts are left behind, and since there is less remaining fresh water to dilute them, their concentration increases.

Irrigated agriculture, especially in acid areas, is always vulnerable to an accumulation of salts due to this evaporation on the cropland itself. The salinity is enhanced by the increased evaporation in storage reservoirs that typically accompany irrigation projects. In addition irrigation drainage water may dissolve more salt from soils with which it comes in contact further increasing its salinity. As a result, irrigation water is always higher in salinity than the supply water and with every reuse, its salt concentration increases even more. In rivers that are heavily used for irrigation, the salt concentration progressively increases downstream as the volume of water available to dilute salts decreases due to evaporation and diversions.

Eutrophication And Algal Nutrients

Eutrophication is a process of providing a water body with nutrients for the aquatic life it, supports. A lake starts its life as a clean body of water. Small amounts of nitrates and phosphates occur in all aquatic systems and these are sufficient to maintain a balanced biological growth (a balance between the production of aquatic life and its destruction by bacterial decomposition). With the introduction of nutrients through land run off and growth and decay of aquatic life, the lake collects good amount of organic substances. Thus when unusually large concentrations of nutrients are present in water bodies, there is an excess of growth of algae known as algal bloom. This produces an unsightly green slime layer over the surface of water body. This slime layer reduces the penetration of light and restricts atmospheric reoxygenation of the water. The dense algal growth eventually dies and the subsequent biodegradation produces oxygen deficit which can result in foul smelling anaerobic conditions. The anaerobic conditions created by rotting algae can present health hazard to aquatic systems.

Thus with large inputs of nutrients from human sources, the bacterial decomposition cannot keep pace with the productivity and sedimentation is accelerated, whereby eutrophication only is favoured. Lakes can be protected from eutrophication only by providing measures for sewage treatment and preventing the sewage from entering the water bodies.

Organic Pollutants

§ Sewage

§  Agriculture run-off

§ Pesticides

§  Oil § Soap, detergents

§  Polychlorinated biphenyls (PCBs)

§  Polyaromatic hydrocarbons (PAHs)

§  Polychlorinated Dibenzodioxins (PCDDs)

§  Polychlorinated Dibenzofurans (PCDFs)

Sewage

Ø  From household and industries sugar, sweet, glucose, starch, cellulose, sucrose, glycogen, dextrin, alginic acid, amino acids, albumin, gelatin, casein and keratin etc are added to water.

Ø These compounds undergo putrefaction by bacterial action to release sulphur and phosphorous compounds like H₂S and SO₂ which in turn cause putrid and musty smell in water.

Ø Both treated & untreated  municipal sewage rich in nitrates & phosphates  are discharged in water enhance cultural eutrophication.

Agriculture run-off

Ø Run-off from agricultural lands supply plant nutrients that stimulate  unwieldy growth of algae and other aquatic weeds.

Ø The water body loses all its D.O. due to the natural biological process of eutrophication and ends up as a dead pool of water

Pesticides

 There are three main groups of synthetic organic insecticides: organochlorines (also known as chlorinated hydrocarbons), organo phosphates, and carbamates. In addition a number of herbicides, including the chlorophenoxy compounds 2,4,5-T (trichlorophenoxy acetic acid, which contains the impurity dioxin, which is one of the most potent toxins known) and 2,4-D (dichlorophenoxyaceticacid) are common water pollutants.

Organochlorine pesticides, such as DDT, have two properties that cause them to be particularly disruptive to food chains. They are persistent, which means they last a long time in the environment before being broken down into other substances and they are quite soluble in lipids, which means they easily accumulate in fatty tissue.

The accumulation of organochlorine pesticides in fatty tissue means that organisms at successfully higher tropic levels in a food chain are consuming food that has successively higher concentrations of pesticide. At the top of food chain body concentrations of these pesticides are the highest, and it is there that organochlorine toxicity has been most recognisable.

Birds, for example , are high on the food chain and it was the adverse effect of DDT on their reproductive calcium metabolism in birds, resulting in eggs with shells that are too thin to support the weight of the parent. The resulting difficulty to reproduce has been shown to affect a number of species, including falcons, bald eagles, ospreys, and brown pelicans.

Other widely used organochlorines included methoxychlor, chlordane, heptachlor, aldrin, dieldrin, and chlordane produce liver cancers, and aldrin,

dieldrin, and endrin have shown to cause birth defects in mice and hamsters.

The organophosphates, such as parathion, malathion, diazinon, TEPP (tetraethylpyrophosphate), and dimethoate, are effective against a wide range of insects and they are not persistent. However, they are much more toxic than the organochlorines that they have replaced.

Propoxur, carbaryl, and aldicarb are some of the popular carbamate pesticides. Acute human exposure to carbamates has led to a range of symptoms, such as nausea, vomiting, blurred vision, and in extreme cases convulsions.

Oil

Ø  Oil pollution may take place because of oil spills from cargo oil tankers on the seas, losses during off-shore exploration and production of oil, accidental fires in ships and oil tankers, leakage from oil pipe-lines, crossing waterways and reservoirs.

Ø Oil pollution results in reduction of light transmission through surface waters, thereby reducing photosynthesis by marine plants.

Ø It reduces the D.O in water and endangers water birds, coastal plants and animals.

Ø Oil films coat the gills of fish affecting their respiration. They enter into streams and eventually clog up sewage work.

Soap and Detergents:

Ø In sewage or an aquatic system, soap generally precipitates as calcium and magnesium salts. Hence any effects that soap might have in solution are eliminated

  2C₁₇H₃₅COO⁻Na⁺ + Ca²⁺ → Ca(C₁₇H₃₅COO)₂(s) + 2Na⁺

Ø Detergents contain from 20 to 30 percent surfactant, and 70 to 80 percent builders.

Ø Surfactants are highly branched long chain carbon compounds.

Ø Detergents are slowly biodegradable because of

  —the branched chain structure of the alkyl groups and

  —benzene rings are attached to tertiary carbon of the branched chain  groups.

Ø Detergents persisted even after biological treatment of the effluent and have contaminated both surface water and ground water with objectionable foaming properties.

Ø Polyphosphates from detergents serve as algal nutrients and thus are significant  as water pollutants.

Polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls, PCBs, are among the most hazardous human made substances. PCBs are extremely stable to heat, chemical, and biological decomposition. They are excellent insulating and cooling fluids, extensively used for many years in  dielectrics (e.g. transformers, capacitors etc), lubricants, and plasticizers. PCBs are also used in hydraulic fluids, lubricating oils, paints, adhesive resins, inks, fire retardants, wax extenders, and numerous other products.

PCBs are ubiquitous in the environment because of indiscriminate dumping in unregulated landfills. Disposal and leakage of industrial fluids into rivers and coastal waters contaminate fish making it a primary dieting source of PCBs.  They resist the degradation and adsorb into soils and colloidal materials in water. Some persist with half-lives of 8-15 years in the environmental compartments. This stability contributes to their dispersion in the environment and long-range air pollution. Because they are lipophilic, these species are stored in fatty tissues and accumulate in food webs. This chemical retards the groth of the foetus through nerve and development impairment.

The physical and toxicological properties and molecular structures of PCBs are related to their degree of chlorination. Substitution of electronegative chlorines at one or more ortho–positions lead to rotation about the bond between phenyl rings. The three most toxic congeners are 3,4,3,\’4\’- tetrachlorobiphenyl, 3,4,3,\’4\’,5\’ – pentachlorobiphenyl and 3,4,5,3,\’4\’,5\’ -hexachlorobiphenyl. Because these have no chlorines at the ortho-positions, the biphenyl rings can be coplanar and structurally resumble dioxin, which is the most toxic organic compound.

In Japan, pregnant women consumed oil contaminated with PCBs that leaked from a heat exchanger, and gave birth to infants who suffered retarded growth, called “Yusho Disease”. 

Polyaromatic hydrocarbons (PAHs)

PAHs are a class of organic compounds produced by incomplete combustion or high-pressure processes. Although produced naturally by forest fires and volcanoes, most PAHs in ambient air are the result of man-made processes. Such processes include

•  burning fuels such as coal, wood, petroleum, petroleum products, or oil,

•  burning refuse, used tires, polypropylene, or polystyrene,

•  coke production, and

•  motor vehicle exhaust

There are approximately 100 different known PAHs in air, soil, foodstuffs,  and water . Benzo(a)pyrene, a potent carcinogen, is commonly used as an  environmental indicator for PAHs. Often, PAHs consist of three or more fused benzene rings containing only carbon and hydrogen. Ø Studies show that certain PAH metabolites interact with DNA and are genotoxic, causing malignancies and heritable genetic damage in humans. Ø In humans, heavy occupational exposure to mixtures of PAHs entails a substantial risk of lung, skin, or bladder cancer.

PAHs are known by several names:

•  polycyclic organic matter (POM),

•  polynuclear aromatic hydrocarbons,

•  polynuclear aromatics (PNAs), and

•  polynuclear hydrocarbons

The more common PAHs include

•  benzo(a)anthracene,

•  benzo(a)pyrene,

•  benzo(e)pyrene,

•  benzo(g,h,i)perylene,

•  benzo(k)fluoranthene,

•  chrysene,

•  coronene,

•  dibenz(a,h)acridine,

•  dibenz(a,h)anthracene,

Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated Dibenzofurans (PCDFs)

Polychlorinated dibenzodioxins are highly toxic and are the by-products in the

 manufacture of chlorophenoxy herbicides and hexachlorophene. The chlorophenoxy herbicides including 2,4,5-trichlorophenoxyacetic acid, were manufactured on a large scale for weed and brush control and as military defoliants. The best known member of the PCDDs group is 2,3,7,8-tetrachlorodibenzo-p-dioxin (often referred to simply as dioxin) which shows very acute toxicity for some species in laboratory tests. Also of concern is the related polychlorinated dibenzofuran group of compounds (PCDFs), the most toxic member once again being 2,3,7,8 tetrachlorinated compound. These compounds are found in the environment in complex mixtures containing PCDDs and PCDFs with all possible substitution patterns. The two group of compounds are formed during the combustion of organic material containing chlorine such as chemical and municipal incinerators, coal-fired power stations and domestic coal fires. They are also found as contaminants in some chlorinated chemical products.

In addition the compound is also likely to accumulate in sediments. There are few investigations of dioxin concentrations in natural water samples (concentrations would be at or below lower detection limits), but many in sediments and living organisms.

Suspended Solids & Sediments

Sediment is soil that is transported by air and water and deposited on the stream bottom. Sediment pollution is an excessive amount of organic and inorganic particles entering the stream system. Sediment can come from developed urban areas and typically includes road stream crossings, storm water runoff, and construction areas. Sediment can also come from farming sources such as croplands and animal crossings or from recreation such as repeated access on eroding banks. Sedimentation is the act or process of depositing sediment. Sedimentation can be caused by spates, which tear at the soil along unprotected banks. Flashy flows, or spates, are when the water level rises and falls extremely quickly during precipitation events.

The proliferation of impervious surfaces in urban areas results in the increase of storm water and its facilitated movement to nearby water bodies. Spates cause flash floods and erosion that can damage habitat both in and out of the water. Sedimentation also contributes to a decrease in water clarity affecting how sunlight penetrates the water, and thus impacting plant growth. Sediment also absorbs heat, warming up the water body, and reduces dissolved oxygen in the water. The amount and consistency of saturated dissolved oxygen is important to some cold-water species, specifically trout and stoneflies. Sedimentation can also cover fish spawning grounds and insect habitat, causing a decrease in fish production and loss of insects as a food source.

Thermal Pollution

Waste heat is an inevitable by-product of the power plants & most manufacturing processes.  A rise in the temperature of rivers or lakes that is injurious to water-dwelling life and is caused by the discharge of heated industrial or  power-plant waste water is called Thermal or Heat pollution.

The warmer water decreases the solubility of oxygen in the water and it also causes water organisms to breathe faster. Many water organisms will then die from oxygen shortages, or they become more susceptible to diseases.

Some species may be eliminated entirely if the water temperature rises by 10 degrees Celsius. Additionally, dissolved oxygen is the key to assimilation of organic wastes by microorganisms. Heating a water body will impair this assimilation.

Thermal pollution not only kills heat intolerant fish, but also plants, thereby disrupting the web of life dependent on the aquatic food chain. Also, the elimination of heat-intolerant species may allow less desirable heat-tolerant species to take over.

The life cycles of many aquatic organisms are closely and delicately geared to water temperature. Fish are often disturbed, migrate, and spawn in response to temperature cues. When water temperature is artificially changed, the disruption of aquatic organisms’ normal activities and patterns can be catastrophic. There may be large-scale migration to an environment more favourable to their survival. The addition of new species of fish will change the eco-balance of the migrated area.

Radionuclides Pollution

Radioactive materials can enter water in several ways:

Ø By being deposited in surface water from the air

Ø By entering ground water or surface water from the ground through erosion, seepage, or human activities such as mining, farming, storm water, and industrial activities.

Ø By dissolving from underground mineral deposits as waster flows through them

Ø By accidental releases of radioactivity, or improper disposal practices.

Some radioactive particles dissolve and move along with the water. Others are deposited in sediments or on soil or rocks.

Most drinking water sources have very low levels of radioactive contaminants. Because these levels are very low, they are not considered to be a public health concern. Radon, from radium sources in the ground, is a special case of dissolved gas that can be at higher levels. Health becomes a concern when radionuclides become concentrated in these bodies of water. Water can pick up radioactive material as it flows through the rocks, soil or cracked cement surrounding a water source, therefore contaminating that water source.

The world has never quite seen an event like the one unfolding off the coast of eastern Japan, in which thousands of tons of radioactively contaminated water from the damaged Fukushima  Daiichi nuclear power plant are pouring directly into the ocean. How this continuing contamination will affect marine life, or humans, is still unclear.