Q 1. (a) Aquatic Pollution is the introduction by man directly or indirectly of substances or energy, which have harmful effects on living resources into the water body. Substances which are capable of destroying the purity of rivers, streams, lakes oceans, etc. and constituting harm to human health and aquatic organisms as well as preventing the use of aquatic environment are all known as Pollutants.

(b) Similarly, if the substances are present in the water body but do not constitute any form of harm to the living organisms, they are referred to as contaminants.

Q 2.  Sources of aquatic pollutants include agricultural wastes, industrial wastes, Oil and domestic sewage.

(A)Agricultural Wastes, such as nutrients (nitrate and phosphate) and pesticides. Pesticides after application on crops in the field get into the aquatic environment through agricultural land run-offs during rainfall. Most of these pesticides are very harmful to fishes and other living organisms in the water. The nutrients are constituents of fertilizer and detergents, which lead to aquatic vegetation bloom and consequent eutrophication.

(B)Industrial Wastes:These include metals, which are major effluents from industries. For example Battery industries that use lead and acid as part of their raw materials and this constitute their wastes, which are harmful to living resources when they get into aquatic environment. In addition large amount of water is used to cool heavy machinery used by many industries. The resulting hot water is usually discharged into water bodies. This increases the temperature of the water body and could impair many biological activities in the water.

(C) Domestic Wastes: These are released into the aquatic environment in form of detergents, cans generated from used pesticides, canned foods and other consumables. All these pollute water and have effects on living resources in the aquatic environment.

(D) Radioactive Pollution
Radioactive materials may enter the sea from two main sources, which are weapon testing via atmospheric fall-out and from atomic power industries.  Some highly dangerous radioactive wastes are disposed of by dumping them into the deep ocean in sealed containers. An example is the solid waste at Koko village, Delta State-Nigeria where radio-active materials were dumped.

(E) Thermal Pollution
   Warm effluent discharged into the aquatic system including waste water used to cool industrial machinery may raise the water temperature and prevent the hatching of fish eggs and those of other biota. The increased water temperature may alter the metabolic rate of organisms within the system, affect their reproduction, causing them stress, hyperactivity, reduced growth or even death. It would reduce the solubility of oxygen, exacerbated by increased biochemical oxygen demand occasioned by animals and bacteria and by reduced vertical mixing due to thermal stratification. Migratory fish such as salmon may be discouraged from passing through the area.

(F) Oil.These include crude oil or its by-products, such as kerosene, automotive gasoline oil, etc, that may result from accidental spillage from tankers or pipelines as well as washing of oil tankers in the seas. The oil may drift to the shore or into the deep region of the water body or remain floating" on the water surface. This has a blanketing effect on the water preventing penetration of sunlight    into    the    water    for    photosynthesis    by phytoplankton and also inhibits air-water contact. Oil on water surface clogs the feathers of aquatic birds and impairs their movement. Oil spills are the harmful release of oil into the environment, usually in the water, sometimes killing area flora and fauna. Oil is the most common pollutant in the oceans. More than 3 million metric tons of oil contaminates the sea every year. The majority of oil pollution in the oceans comes from land. Runoff and waste from cities, industry, and rivers carries oil into the ocean. Ships cause about a third of the oil pollution in the oceans when they wash out their tanks or dump their bilge water. It is an unfortunate by­product of the storage and transportation of oil and petroleum is the occasional spill. Oil spills are very difficult to clean up.

Q3. Lead is usually incorporated into gasoline oil as an antiknock agent. Motor vehicles burn off lead releasing it to the atmosphere. It could result to death of plants and accumulates in other living organisms in fish ponds near the road. High concentration of lead is very toxic both to man and aquatic organisms.

Phosphorus is normally incorporated into detergents. Through run off after rains, if the detergent gets into water bodies it can cause death of many aquatic organisms and promote eutrophication. It has been suggested that nitrogen be used in detergents, but nitrogen causes eutrophication as well.  Therefore active enzymes are now introduced to detergents which render phosphorus inactive upon contact with water. 

Mercury is another inorganic pollutant that is very dangerous to both aquatic organisms and man.  They are incorporated in some pesticides used on agricultural lands.  When in contact with water it changes form to ethyl mercury which is very toxic.  It bioaccumulates in fishes and when eaten by man could be carcinogenic and can cause death.
Dichloro-DiphenylTrichloroethane(DDT): this is used against some agricultural pests.  Some of the targeted pests develop resistance and bioaccumulates the chemical.  When they are preyed upon by other organisms including fish, it is capable of causing death.  When DDT gets into fish ponds, it can inhibit hatching of fish eggs.  The use of alternative pesticides is suggested as solution to this problem.
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