Water pollution - types, effects, sources and control of water pollution

Water pollution

Water pollution may be defined as “the alteration in physical, chemical and biological characteristics of water which may cause harmful effects on humans and aquatic life.”

Pollutants include:

1. Sewage
   
2. Industrial effluents and chemicals
   
3. Oil and other wastes
   

Chemicals in air dissolve in rain water, fertilizers, pesticides and herbicides leached from land pollute water.

TYPES, EFFECTS AND SOURCES OF WATER POLLUTION Water pollution is any chemical, biological or physical change in water quality that has a harmful effect on living organisms or makes water unsuitable for desired uses.

Infectious agents
Ex: Bacteria, Viruses, Protozoa, and parasitic worms.

Human sources
Human and animal wastes

Effects: Variety of diseases.

Oxygen demanding wastes (Dissolved oxygen): This degradation consumes dissolved oxygen in water. Dissolved Oxygen (DO) is the amount of oxygen dissolved in a given quantity of water at a particular pressure and temperature.

The saturated point of DO varies from 8 to 15 mg/L Ex: Organic wastes such as animal manure and plant debris that can be decomposed by aerobic (oxygen-requiring) bacteria.

Human sources: Sewage, Animal feedlots, paper mills and food processing facilities.

Effects: Large populations of bacteria decomposing these wastes can degrade water quality by depleting water of dissolved oxygen. This causes fish and other forms of oxygen-consuming aquatic life to die.

Inorganic chemicals
Ex: Water soluble inorganic chemicals:

1. Acids
   
2. Compounds of toxic metals such as lead (Pb), arsenic (As) and selenium (Se)
   
3. Salts such as NaCl in oceans and fluoride (F^-) found in some soils
   

Human sources: Surface runoff, industrial effluents and household cleansers Effects: Inorganic chemicals can:

1. Make freshwater unusable for drinking and irrigation
   
2. Cause skin cancer and neck damage
   
3. Damage nervous system, liver and kidneys
   
4. Harm fish and other aquatic life
   
5. Lower crop yields
   
6. Accelerate corrosion of metals exposed to such water
   

Organic chemicals
Ex: Oil, Gasoline, Plastics, Pesticides, Cleaning solvents and Detergents.
Human Sources: Industrial effluents, household cleansers and surface runoff from farms.

Effects:

1. Can threaten human health by causing nervous system damage and some cancers.
   
2. Harm fish and wildlife.
   

Plant nutrients
Ex: Water soluble compounds containing nitrate, Phosphate and Ammonium ions.
Human sources: Sewage, manure and runoff of agricultural and urban fertilizers.

Effects:

1. Can cause excessive growth of algae and other aquatic plants, which die, decay, deplete dissolved oxygen in water thereby killing fish
2. Drinking water with excessive levels of nitrates lower the oxygen carrying capacity of the blood and can kill urban children and infants.

Sediment
Ex: Soil, silt, etc.
Human Sources: Land erosion

Effects:

1. Causes cloudy water thereby reducing photosynthetic activity
2. Disruption of aquatic food chain
3. Carries pesticides, bacteria and other harmful substances
4. Settles and destroys feeding and spawning grounds of fish
5. Clogs and fills lakes, artificial reservoirs, stream channels and harbours.

Radioactive materials:
Ex: Radioactive isotopes of:

1. Iodine
2. Radon
3. Uranium
4. Cesium and
5. Thorium

Human sources: Nuclear power plants, mining and processing of uranium and other ores, nuclear weapon production and natural sources.

Effects: Genetic mutations, birth defects and certain cancers.

Heat (Thermal pollution)
Ex: Excessive heat

Human sources: Water cooling of electric power plants and some types of industrial plants. Almost half of whole water withdrawn in United States each year is for cooling electric power plants.

Effects

1. Low dissolved oxygen levels thereby making aquatic organisms more vulnerable to disease, parasites and toxic chemicals.
2. When a power plant starts or shuts down for repair, fish and other organisms adapted to a particular temperature range, can be killed by an abrupt temperature change known as thermal shock.

Point and non-point sources of water pollution:
Point sources These are pollutants that are discharged at specific locations through pipes, ditches or sewers into bodies of surface waters.

1. Ex: Factories, sewage treatment plants, abandoned underground mines and oil tankers.
2. Non point sources These pollutants cannot be traced to a single point of discharge. They are large land areas or air-sheds that pollute water by runoff, subsurface flow or deposition from the atmosphere.
   Ex: Acid deposition, runoff of chemicals into surface water from croplands, livestock feedlots, logged forests, urban streets, lawns, golf courses and parking lots.

Control measures of water pollution

1. Administration of water pollution control should be in the hands of state or central government
2. Scientific techniques should be adopted for environmental control of catchment areas of rivers, ponds or streams
3. Industrial plants should be based on recycling operations as it helps prevent disposal of wastes into natural waters but also extraction of products from waste.
4. Plants, trees and forests control pollution as they act as natural air conditioners.
5. Trees are capable of reducing sulphur dioxide and nitric oxide pollutants and hence more trees should be planted.
6. No type of waste (treated, partially treated or untreated) should be discharged into any natural water body. Industries should develop closed loop water supply schemes and domestic sewage must be used for irrigation.
7. Qualified and experienced people must be consulted from time to time for effective control of water pollution.
8. Public awareness must be initiated regarding adverse effects of water pollution using the media.
9. Laws, standards and practices should be established to prevent water pollution and these laws should be modified from time to time based on current requirements and technological advancements.
10. Basic and applied research in public health engineering should be encouraged.