Water Pollution, Chemistry tutorial


In sciences 'contamination' terms to a circumstances whenever a chemical substance is present in a specified example or matrix through no proof of harm while "pollution" is utilized in cases where the attendance of the chemical is causing harm. Pollutants consequently are chemicals causing environmental harm.

Broadly, our environment can be classified into water, air and soil environments. Therefore we talk of water pollution, air pollution and soil pollution. In many cases, the categorization has no clear-cut boundary as a pollutant originate in air might soon discover its way into the soil or aquatic environment and vice versa.

Pollutants in Aquatic Ecosystems

Effects and Criteria of Pollutant Designation

Any chemical can become a pollutant in water if it is present at a elevated concentration. For instance, serious pollution incident can consequence from spill of sugar and milk. When a water body becomes polluted, one or more of the subsequent results would be experienced:

Aesthetic or illustration nuisance including production of foul smell.

  • Heightened temperature of the water body.
  • Lack of oxygen or devaluation of melted oxygen.
  • Acute or chronic toxicity causing damage to aquatic or human life.
  • Disturbance of the ph regime.
  • Eutrophication for example much availability of nutrients giving increase to extreme enlargement of several organisms in water.

 Even though any chemical can be a pollutant, indeed chemicals have been recognized via international agreement as being 'priority pollutants'.

Such priority  pollutant  chemicals  have  been  selected  depend on  the subsequent criteria: (i) they are  toxic at  low  concentrations; (ii) they bioaccumulate; (iii) they are persistent; and (iv)  they are  carcinogens (materials that can cause cancer).

It is true that priority pollutants can be extremely dangerous or hazardous even at low concentrations, but then; dissimilar chemicals can constitute priority pollutants in different contexts. For instance, effluents enclosing biodegradable organic chemicals generally act as pollutants not since they enclose chemicals at concentrations that are toxic, but since they enclose chemicals that give abundant food for microorganisms. The microorganisms thus multiply rapidly as a result of the increased food input. The microorganisms, in the process of growing and oxidizing the organic chemical foodstuff, utilize up the dissolved oxygen quickly leading to the death of higher organisms as fish.

Modes of Chemical Pollutant Release

There are 2 broad kinds of chemical liberate into an environment, namely: point source discharge or direct discharge and non-point source discharge or spread discharge. Point source or direct discharge is liberated of environmental pollutants from an exact place these as industrial sites, sewage works or agricultural land. Pollution from point source discharges are easier to monitor, control, and their environmental influences is comparatively easier to find out. On the other hand, the non- point discharge of pollution terms to pollution from diffuse or even diverse places for example heavy metal pollution arising from harmattan loesses deposition. These pollution sources are generally hard to find out, and extremely often, statistical weapons these as factor analysis are resorted to in order to reliably predict their sources.

Currently, emphasis on priority pollutant control has shifted from control of point sources towards contro ofdiffuse sources.This is because new technology enabling priority pollutant is now available and pollution control technology has improved tremendously. In some cases however, the availability of new technology only partially solves the existing problem, for example, hydro chlorofluorocarbons (HCFCs) are preferred to the chlorofluorocarbons (CFCs) because HCFCs are expected to break down in the atmosphere fairly rapidly. However, the trifluoroacetic acid, which some HCFCs are expected to produce, is very stable and will wash out from the atmosphere whenever rain falls. In areas like seasonal wetlands which have high evapotranspiration rates, the trifluoroacetic acid may concentrate to levels which may damage plants.

Pollution Control: Regulation and Control of Priority Pollutants

The growing internationalization of priority pollutants control is mostly driven by the recognition that pollution does not recognize environmental compartmental or national boundaries. For example, a pollutant can cross from soil to aquatic environment. Likewise, pollution caused in London may soon find expression within the geographical boundary of Nigeria. It has been recognized also that protection of aquatic environments (marine water particularly) can only be accomplished by international action.

Government, regulatory agencies and industrial initiatives have recognized the following hierarchy of approaches to priority pollutant control: Replace - use another, more environmentally friendly chemical; Reduce - use as little of the priority pollutants as possible; and Manage - use in a way to eliminate or minimise accidental or adventitious loss and waste.

The regulation and control of priority pollutants is an international issue and is not just a case of tightening up on discharge consents as diffuse sources can be important and even dominate in some cases.  It also requires a portfolio of complementary activities based on a hierarchy of replace - reduce - manage.

Individual Aquatic Environment Pollutants: Their Sources and Effects

A wide range of pollutants can enter the aquatic, or more specifically, the marine environments in a number of ways.  These pollutants or classes of pollutants are:

Crude oil

Since crude oil is a very complex mixture of many different chemicals, the effects of an oil spill on the aquatic environment depend on the exact nature and quantity of the oil spilled. The effects are also determined by such other factors as the prevailing weather conditions and the ecological characteristics of the affected region.

Crude oil gets into water bodies through transportation (tanker operations and accidents, dry docking and non-tanker accidents), fixed installations (coastal refineries and offshore production) and other sources (municipal wastes, industrial wastes, urban run-off, atmospheric fallout and ocean dumping). Several of the damages caused to aquatic organisms via oil spills are development inhibition of phytoplankton, huge level mortality in littoral communities through acute toxicity and smothering, fish kill, death of seabirds through drowning, hypothermia or toxic consequences of ingested oil and vulnerability of coastal populations of marine mammals for example seal colonies.


Domestic sewage, through or with no the presence of industrial wastes, probably represents the commonest and most extensive contaminant of inshore and near shore waters. Sewage might accomplish the water bodies in different shapes: untreated raw sewage discharges, partially or properly treated discharge and outright dumping of associated sewage sludge at marine sites. Sewage poses aesthetic and health risks to human populations and as well acts as a vector whereby a considerable variety of other contaminants reach the aquatic environment.

Persistent organic chemicals

Persistent organic chemicals which have proved to be of concern in the aquatic environments are essentially chlorinated pesticides such as DDT, dieldrin, aldrin, endrin, lindane,  hexa chlorobenzene and toxaphene. Others include polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF); pesticides like 2, 4 - dichlorophenoxyacetic acid (2,4-D), 2,4,5 - trichlorophenoxyacetic acid (2,4,5-T) and 2-methyl-4,6-dichlorophenoxyacetic acid (MCPA). There are other chemicals which are sufficiently common, toxic and persistent to represent potential threats for example polycyclic aromatic hydrocarbons (PAHs), plasticizers (e.g. phthalate esters), detergent residues, organic solvents, and so on.

These chemicals contaminate the aquatic systems through aerosol drift, surface runoff, aerial spray and direct application on water hyacinth or mulluscs. Amongst the top predators, the main deleterious effects have been eggshell thinning in birds (by DDE) and interference with the reproductive and immune system in mammals (by PCBs). A considerable number of top predator birds showed major declines in abundance during the peak period of DDT usage. Apparently responsible for the abnormalities in male sex development in wildlife and humans including members of the DDT family of compounds, chlordecone (Kepone), various sterols and possibly nonylphenol. Of these, p, p′- DDE is the most potent.

Heavy metals

Metals and metalloids with an atomic density (greater than 6g/cm3) which are associated with pollution and toxicity problems are generally referred to as heavy metals. Examples are As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. Unlike most organic pollutants, heavy metals occur naturally in rock-forming and ore minerals. So, there is a range of normal background concentrations of these elements in soils, sediments, waters and living organisms. Thus, the presence of the metal is an insufficient evidence of pollution (we  only  talk of pollution when there is high concentration of the metals relative to the normal background levels).

Heavy metals find wide applications in electronics, machines and the artifacts of everyday life as well as "high-tech" applications. Hence, they tend to reach the environment from a vast array of anthropogenic sources as well as natural geochemical processes. Depending on their speciation (as well as one the condition of the organism), heavy metals like Hg, Pb and Sn in the aquatic environments are potentially harmful.


The addition of excess nutrients to a water body is identified as eutrophication. Significant sources of such nutrients comprise breakdown of organic matter, phosphorus-enclosing detergents, agricultural runoff and leaching of artificial fertilizers and manures from intensive farming units, the burning of fossil fuels that enhances the nitrogen content of rain, and so on and so forth. Nitrogen and phosphorus are the 2 nutrients most associated in eutrophication. This is since expansion of organism in water bodies is generally limited via phosphorus rather than nitrogen; it is enhance in phosphorus that stimulates excessive plant production in freshwaters.

One of the serious consequences of eutrophication that effect in huge financial loss is the stimulation of algal growth especially in water supply reservoirs; this is the major cause of water treatment problems. Huge populations of algae might effect in the blocking of filters in the treatment works.

Drinking water through elevated nitrate contents presents potential health difficulties. In particular, babies under 6 months of age who are fed through these water might expand methaemoglobinaemia (blue baby syndrome), in which the nitrate in their feeds is decreased to nitrite in their acid stomachs. The nitrite then oxidizes ferrous ions in their blood haemoglobin, thus lowering its blood bearing capacity.


Commonly, there  are  3 categories  of  water  by  respect  to  their acidity differences; (i) those that are permanently acidic by a pH < 5.6;  (ii)  those which are occasionally acidic, where pH  is generally above 5.6, but might drop below 5.6 periodically; and (iii) those which are never acidic, the pH never dropping  below 5.6. The acids either fall straight into water bodies in form of precipitation or are washed in from vegetation and soils inside the catchments. Sometimes, acids can be produced indirectly from mining activities. For instance, exposed iron pyrites can undergo chemosynthetic bacterial oxidation to yield sulphuric acid, making water flowing from the area to have a pH of 3.5 or below.

When there is acidification of a water body, among the animals to 1st disappear are the shrimps, minnows, trout and crayfish. Usually, no species of fish reproduces at values of pH below 5.4.  

Thermal pollution

Water utilized for cooling discharge from electricity generating stations is the major source of pollution via heat. An enhancement in temperature alters the physical environment in terms of a reduction in both the density of the water and its oxygen concentration, while the metabolism of organisms enhances.

Cold water species (of fish especially) are extremely sensitive to transforms in temperature and tend to disappear if heated effluents are discharged to the headwaters of streams.  As the temperature  increases, a conflict arises; the rate of heart-beat of a fish increases to attain oxygen for raised metabolic  procedures,  but  at  the  similar  time,  the  oxygen concentration of the water is decreasing.


Sea water and marine sediments are logically radioactive since of the natural  presence  of  radioactive  potassium  40,  uranium  and  thorium decay  series,  and  the  formation  of  lighter  radioisotopes  through  the interaction of cosmic rays and atmospheric  gases,  through  the products subsequently conveyed to the water surface. Chemically, radionuclides act almost identically to their stable counterparts. They are, hence, partitioned between water, sediments and biota according to their behavioral properties for instance Cs-137 is mainly water soluble, Pu-239 and Pu-240 form strong connections through fine-grained sediments.

Liberates of radioactivity via anthropogenic activities into the aquatic/marine environment include: (i) radiation from Weapons Testing Programmes; (ii) routine liberates from Nuclear  Power Plants for instance tritium, sulphure-35, zinc-65 and cobalt-60; (iii) liberates from Nuclear Fuel Reprocessing Plants for example tritium, C-14, C0-60,  Sr-90, Te-99, Ru- 106, I-129, Cs-134 and 137, Ce-144, Pu-241 and Am-241; (iv) reactor accidents on land for instance Chernobyl in the Ukraine (April, 1986) nuclear reactor accident; (v) dumping of low level waste for example Radioactive substance dumped at Koko village in Nigeria; and (vi) naval sources for instance nuclear warheads and reactors from accidents to submarines.

Humans are the most susceptible of all living organisms to the consequences of radiation, consequently all radiological population calculates are designed to shield humans on the understanding that all other species will hence automatically obtain adequate protection. Radiation results on humans are either somatic or genetic. Somatic consequences are those that cause (noticeable) injure to the individual for instance anemia, fatigue, loss of hair; cataracts, skin rash and cancer. Genetic results comprise inheritable changes consequential from mutations in reproductive cells. It is extensively detained that even tiny dosages of radiation can have several unpleasant effects, genetic effects being of hugest concern.

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