Transcript Water Pollution

Water resource
And
pollution
Dr. Ho, Wing Shing
Environmental Science Programme
Impact of water resource
•Hydropower
•Agricultural benefits
•Industrial base
In general, scarcity of flesh water resources and
the tremendous costs of developing new
resources have a significant impact on
development and economic growth:
-
Natural
industrial
agricultural
human
Policy is required to maintain the
water resource:
1.Water resource management plan
2.Industry standards relating to water
consumption and effluent discharges
3.Implementation of the Environmental
regulation
4.Proper surveillance systems for drinking
water sources and supply schemes.
Water Pollution
Human activity is the first pollution
problem.
In human history, people naturally settled
near a source of water, e.g., lakes, rivers,
and in areas where well water was
available.
As a result, the water often become
contaminated with
-human wastes
-disease-causing microorganisms from human
and animal wastes.
Water-borne diseases have been virtually
eliminated in the industrialized countries.
However, sewage systems are often inadequate
in under-developed countries.
Types of water pollutants
1. Disease-causing agents
-feces from people infected with
pathogens
Coliform bacteria count: test water for
contamination by microorganisms.
The presence of Coliform bacteria is an
indication of fecal contamination.
2. Oxygen-consuming wastes:
they are from
·
·
·
human
animal
industrial wastes
- oxygen is not very soluble in water
- oxygen solubility depends on the
temperature and the altitude of the water
- aquatic plants and animals depend on the
oxygen level in water.
Dissolved oxygen is rapidly depleted if organic
waste materials are released into the water.
Organic wastes are decomposed by:
(a) aerobic (oxygen-consuming) bacteria and
fungi.
If the concentration of dissolved oxygen falls
< 5 ppm, fish start to die.
(b) anaerobic (no-oxygen required) bacteria: in
complete absence of oxygen, decomposition
of organic matter can be carried out.
End products
Aerobic
Anaerobic
CO2 (carbon dioxide) CH4 (methane)
NO3- (nitrate)
NH3 and amines
SO42- (sulphate)
H2S (hydrogen sulphide)
PO43- (phosphate)
PH3 and other P compounds
Plant nutrients: from some of the
end products
Aquatic plants need nitrogen and phosphorus
for proper growth.
If a new source of nitrogen or phosphorus is
introduced into the water, excessive plant
growth occurs, and the algae population
explodes (on surface).
* The water becomes turbid.
3. Suspended/dissolved solids and
sediments
The natural erosion of rock and soil produces
undissolved particles (sediments):
clays, sand, silt
Suspended particles make water turbid, reduce
light penetration and lower rate of
photosynthesis.
As sediments settle, they can bury bottomdwelling organisms and fish spawning
grounds:
disrupting aquatic habitats.
Sediments problems:
- filling irrigation ditches
- clogging harbors and lakes
- cause aggregation of toxic substances
Dissolved solids contain ions e.g.,
Concentration (ppm)
Ion
Fresh Water
Seawater
HCO3- (bicarbonate)
41
0.2
Ca2+ (calcium)
16
0.9
Mg2+ (magnesium)
14
4.9
Na+ (sodium)
11
41
Cl- (chloride)
8.5
49
The ions are essential for the normal growth of most life forms.
Saline water: abnormal high concentration of dissolved ionic salts.
Causes/sources of saline water:
1. Irrigation is the main cause of increased
salinity in natural waters; salts tend to
accumulate on the soil surface.
2. Run off from the land carry an increased
load of dissolved salts.
3. Discharges from industrial and
municipal waste-treatment plants.
4.Toxic Substance (metals, organic
chemicals)
Ingestion causes harm by interfering
with organism’s normal metabolic processes.
Causes
1. Bioaccumulation: a toxic substance
becomes more concentrated as it moves
upward through the food chain in the
ecosystems.
Measuring the concentration of a toxin in fish
is a useful guide to toxic pollution in water.
2. Industrial activities and farming
Excessive Toxic metals: form complexes
with proteins, consequently, the complexes
cause
brain damage
kidney disorders
- liver disorders
Mercury, lead and cadmium – widespread
use and toxicity
Mercury: - only liquid metal at
room
temperature
can be vaporized in air
component of many rocks
methyl mercury is very
soluble
Lead
used as solder, battery, alloys, paints,
gasoline, etc.
- it has virtually been eliminated from
gasoline, paint, battery
particular toxic to young children (retard
brain development), and
adults: causes neurological disorders,
bioaccumulates in bones.
- can be vaporized in air
Cadmium in paints, plastics, battery
leafy vegetables absorb cadmium
from water and soil
accumulates in the liver
causes cancer in liver, kidney and
lung disease
Organic compounds
present or used as insecticides,
herbicides, detergents, oil and radioactive
substances, etc.,
when chemicals enter water supplies,
some of these can cause health and
environmental problems.
Of particular concern:
Organic
chlorine
compounds
(polychlorinated hydrocarbons) e.g., DDT
(dichlorodiphenyl trichloro ethane), dioxin
and PCBs (poly chlorinated biphenyls).
do not easily break down into nontoxic products: persist in the environment
pose a threat to aquatic life
bioaccumulate in fatty tissues of fish,
birds and humans through food chains
5.Thermal Pollution (heat pollution)
from cooling system (heated water) of
electric power plants.
warmer water increases respiration rates;
As a result, increase oxygen consumption, but
solubility of oxygen in water decreases with
rising temperature.
higher temperature can affect aquatic life:
heat-sensitive fish, egg hatching, etc.—
disrupting life cycle of some organisms and
balance of the ecosystems.
6. Pollution of groundwater
-contaminated with hazardous substances
from dumpsites containing waste
chemicals,
e.g., paints, metals, textiles, fertilizers,
insecticides, petroleum products, etc.
References
1. Phyllis E. Buell, James E. Girard,
Chemistry Fundamentals: An environmental
perspective. Prentice-Hall, 2nd ed., 2003.
2. Richard Wright, Environmental
Science, Action for a sustainable future, The
Benjamin/Cummings, 9th ed., 2005.
3. Charles E. Kupchella, Margaret C.
Hyland, Environmental Science, Living
within the system of nature, Prentice-Hall,
3rd ed., 1993.