2. Case Study: LeadCase Study: Lead
Does not break down in environmentDoes not break down in environment
(element)(element)
NeurotoxinNeurotoxin
Poisonings have dropped dramatically in U.S.Poisonings have dropped dramatically in U.S.
Leaded gas banned 1976, phased out 1986Leaded gas banned 1976, phased out 1986
Lead-based paints 1970, used illegally untilLead-based paints 1970, used illegally until
19781978
Still some U.S. poisonings:Still some U.S. poisonings:
Peeling paint, pipesPeeling paint, pipes
Still used in a few countriesStill used in a few countries
4. Case Study: LeadCase Study: Lead
Lead is especiallyLead is especially
harmful to childrenharmful to children
Figure 22-24Figure 22-24
5. Case Study: MercuryCase Study: Mercury
Does not break down in environmentDoes not break down in environment
(element)(element)
NeurotoxinNeurotoxin
Sources:Sources:
Natural – rocks, soil, volcanoes, vaporization fromNatural – rocks, soil, volcanoes, vaporization from
ocean – approx.1/3 of that released to atmosphereocean – approx.1/3 of that released to atmosphere
Human sources – burning coal (66%) andHuman sources – burning coal (66%) and
incinerating wastes and industriesincinerating wastes and industries
can build to high levels in some types of fish.can build to high levels in some types of fish.
Disperses worldwide, condensesDisperses worldwide, condenses
in colder climates – Arctic is a sinkin colder climates – Arctic is a sink
Bioaccumulates and biomagnifiesBioaccumulates and biomagnifies
6. Case Study: MercuryCase Study: Mercury
Human exposure:Human exposure:
Inhale vaporized elemental mercury or inorganicInhale vaporized elemental mercury or inorganic
mercury saltsmercury salts
Eat fish contaminated with methylmercuryEat fish contaminated with methylmercury
(converted from inorganic mercury by bacteria) –(converted from inorganic mercury by bacteria) –
results in fish advisoriesresults in fish advisories
8. Fig. 22-25, p. 542
BIOMAGNIFICATION
IN FOOD CHAIN
SEDIMENT
PRECIPITATIONPRECIPITATION WINDSWINDS
AIR
WATER
Inorganic mercury
and acids
(Hg2+
)
Inorganic
mercury
and acids
(Hg2+
)
Organic
mercury
(CH3Hg+
)
Inorganic
mercury
(Hg2+
)
Hg2+
and acids
Runoff of Hg2+
and acids
Large fish
Small fish
ZooplanktonPhytoplankton
Hg and SO2
Hg2
+ and acids
Human sources
Incinerator
Coal-
burning
plant
Elemental
mercury
vapor
(Hg)
Photo-
chemical
Oxidation
Elemental
mercury liquid
(Hg)
Deposition
Deposition
Bacteria
Bacteria
and acids
Settles
out
Settles
out
Settles
out
Vaporization
Deposition
Deposition
9. Fig. 22-26, p. 543
Solutions
Mercury Pollution
Phase out use
of mercury in
all products
unless they
are recycled
Require labels
on all products
containing
mercury
Switch from
coal to natural
gas and
renewable
energy
resources
such as wind,
solar cells,
and hydrogen
Convert coal to
liquid or
gaseous fuel
Collect and
recycle mercury-
containing
electric
switches, relays,
and dry-cell
batteries
Tax each unit of
mercury emitted
by coal-burning
plants and
incinerators
Sharply reduce
mercury
emissions from
coal-burning
plants and
incinerators
Prevention Control
Remove
mercury from
coal before it
is burned
Phase out waste
incineration
10. Fig. 22-26, p. 543
Solutions
Mercury Pollution
Phase out use
of mercury in
all products
unless they
are recycled
Require labels
on all products
containing
mercury
Switch from
coal to natural
gas and
renewable
energy
resources
such as wind,
solar cells,
and hydrogen
Convert coal to
liquid or
gaseous fuel
Collect and
recycle mercury-
containing
electric
switches, relays,
and dry-cell
batteries
Tax each unit of
mercury emitted
by coal-burning
plants and
incinerators
Sharply reduce
mercury
emissions from
coal-burning
plants and
incinerators
Prevention Control
Remove
mercury from
coal before it
is burned
Phase out waste
incineration
Editor's Notes
Figure 22.25
Science: cycling of mercury in aquatic environments, in which mercury is converted from one form to another. The most toxic form to humans is methylmercury (CH3Hg+), which can be biologically magnified in aquatic food chains. Some mercury is also released back into the atmosphere as mercury vapor. QUESTION: What is your most likely exposure to mercury?
Figure 22.26
Solutions: ways to prevent or control inputs of mercury into the environment from human activities—mostly through coal-burning plants and incinerators. QUESTION: Which four of these solutions do you believe are the most important?