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.