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Chapter 22
Water Pollution
Types of Water Pollution
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Water pollution
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Any physical or chemical change in water that
adversely affects the health of humans and
other organisms
Varies in magnitude and type of pollutant by
location
Major water pollution issue globally
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Lack of disease-free water
Types of Water Pollution
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Eight categories
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Sewage
Disease-causing agents
Sediment pollution
Inorganic plant and algal nutrients
Organic compounds
Inorganic chemicals
Radioactive substances
Thermal pollution
Some categories are interrelated
Sewage
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The release of wastewater from drains or
sewers
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Includes human wastes, soaps, and detergents
Causes 2 serious environmental problems:
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Enrichment
Increase in Biological Oxygen Demand (BOD)
Enrichment
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Fertilization of a body of water by high
levels of plant and algal nutrients (nitrogen
and phosphorus)
Microorganisms decompose materials into
CO2, water, other inoffensive materials
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Cellular respiration – requires oxygen
Biological Oxygen Demand
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Amount of oxygen needed by
microorganisms to decompose biological
wastes
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Expressed as mg of DO/L for a specific
number of days at a given temperature
As BOD increases Dissolved Oxygen (DO)
decreases
Dissolved Oxygen
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Oxygen has a limited ability to dissolve in
water
When aquatic ecosystem contains a large
amount of sewage, decomposing organisms
use up most of DO
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Little left for fishes and other aquatic animals
Extremely low DO, anaerobic microorganisms
produce compounds with unpleasant odors
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Further deteriorates water quality
Dissolved Oxygen
Oligotrophic Lake
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Unenriched, clear water that supports
small populations of aquatic organisms
Eutrophic Lake
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Slow-flowing stream, lake or estuary
enriched by inorganic plant and algal
nutrients such as phosphorus
Often due to fertilizer or sewage runoff
Eutrophication
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Enrichment of lake, estuary, or slowflowing stream by inorganic plant and algal
nutrients
Increased photosynthetic productivity
Water becomes cloudy (pea soup-like)
because of presence of algae and
cyanobacteria
Eutrophication
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Over time, bodies of water become
eutrophic naturally
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Slowly grow enriched, shallower
Plants start to take root
Becomes a marsh
Artificial eutrophication – human-induced
process
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Fertilizer runoff and sewage
Disease-causing Agents
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Infectious organisms
that cause diseases
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Originate in the wastes
of infected individuals
Common bacterial or
viral diseases:
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Typhoid, cholera,
bacterial dysentery,
polio, and infectious
hepatitis
Disease-causing Agents
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Monitored by testing for presence of E.
coli in the water via a fecal coliform test
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Indicates the presence of pathogenic organisms
E. Coli
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Safe drinking water – no more than 1
bacterium/100 mL
Safe swimming water – no more than
200/100 mL
Safe general recreation water (boating) –
no more than 2000/100 mL
Raw sewage – several million/100 mL
Sediment Pollution
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Excessive amounts of suspended soil
particles
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Originates from erosion of agricultural lands,
forest soils exposed by logging, degraded
stream banks, overgrazed rangelands, strip
mines, and construction
Problems
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Limits light penetration
Covers aquatic animals and plants
Brings insoluble toxins into waterways
Sediment Pollution
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Makes water turbid (cloudy)
Extreme turbidity
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Reduces number of photosynthetic algae and
plants that require light for photosynthesis
Decreases number of aquatic organisms that
feed on producers
Sediments can form layer over coral reefs
or shellfish beds that can clog gills and
feeding structures of aquatic animals
Sediment Pollution
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Particles can also carry toxic chemicals
(inorganic and organic) into water
Can also transport disease-causing agents
Sediment Pollution
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1998 EPA study – sediments in 7% of
watersheds are so seriously contaminated
with toxic pollutants that eating fishes
from those waterways would threaten
human health
Sediments can fill in waterways – problem
in lakes and channels through which ships
have to pass
Inorganic Plant and Algal Nutrients
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Chemicals such as nitrogen and phosphorus
that stimulate the growth of plants and
algae
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Sources:
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Essential for normal functioning of healthy
ecosystem
Harmful in large concentrations
Human and animal wastes, plant residues,
atmospheric deposition, and fertilizer runoff
Causes:
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Enrichment, bad odors, and a high BOD
Mississippi Dead Zone
Mississippi Dead Zone
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Fertilizer runoff from midwestern fields,
manure runoff from livestock operations
1998 Senate Agriculture Hearings -- US
livestock produce 20 times the feces and
urine that humans do
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Not covered by water quality laws
Do not go to wastewater treatment plants
Mississippi Dead Zone
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Dead zone extends from sea floor up into
water column to within several meters
from surface
Floods and droughts change its size
Persists from March/April to September
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Most severe in June, July, August
2002 – more than 22,000 km2 – size of
Massachusetts
Mississippi Dead Zone
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No life other than anaerobic bacteria
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Active swimmers avoid area
Bottom dwellers suffocate
Hypoxia affects more than 146 coastal
areas in world
Organic Compounds
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Chemicals that contain carbon atoms
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Natural examples: sugars, amino acids, and oils
Human-made examples: pesticides, solvents,
industrial chemicals, and plastics
Organic Compounds
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2002 USGS Study of 139 streams in 30
states:
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Tested for 95 organic compounds
Found low concentrations of 82 compounds
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One found in 80% of streams
More than 1/3 contained traces of 10 or more
Effects on human health largely unknown
Inorganic Chemicals
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Contaminants that contain elements other
than carbon
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Examples: acids, salts, and heavy metals
Do not degrade easily
Lead
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Found in old paint, industrial pollutants,
leaded gasoline
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1978 – lead paint banned
1986 – leaded gasoline outlawed
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Dust released into atmosphere, contaminates soil,
especially inner cities near highways
Contaminates soil, surface water, and
groundwater when incinerator ash dumped in
landfills
Pesticides, fertilizers
Food cans and certain types of dinnerware
Mercury
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Vaporizes at room temperature
Coal-fired power plants release 40% of
mercury in environment
Fluorescent lights and thermostats
Also released during metal smelting
Mercury bioaccumulates in the muscles of
top predators of the open ocean
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Human exposure primarily due to eating fishes
and marine mammals
Radioactive Substances
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Contain atoms of unstable isotopes that
spontaneously emit radiation
Sources
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Mining
Processing radioactive materials
Nuclear power plants
Natural sources
Thermal Pollution
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Occurs when heated
water produced during
industrial processes is
released into
waterways
Organisms affected
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Temperature affects
reproductive cycles,
digestion rates, and
respiration rates
Warm water holds less
DO than cold water