Transcript Chapter 15: Environmental Health, Pollution, and Toxicology

Chapter 15:
Environmental Health,
Pollution and Toxicology
Disease
• Disease is often due to an
imbalance resulting from poor
adjustment between the individual
and the environment.
– Continuum from state of health to
disease
– Gray zone in-between
– As a result of exposure to chemicals
in the environment we may be in the
midst of an epidemic of chronic
disease.
Disease
• Seldom have a one-cause-oneeffect relationship w/ the
environment
• Depends on several factors
– Physical environment
– Biological environment
– Lifestyle
Disease
• Chances of experiencing serious
environmental health problems
and disease depends on
– The
– The
– The
– The
water we drink
air we breathe
soil we grow crops in
rocks we build our homes on
Disease
• Natural processes can release
harmful materials into the soil,
water or air.
• Lake Nyos in Cameroon, Africa
– Experienced sudden release of carbon
dioxide
– Killed 1,800 people in near by town.
Terminology
• Polluted environment
– impure, dirty, or otherwise unclean.
• Pollution refers to the occurrence of
unwanted change in the environment
– introduction of harmful materials or the
production of harmful conditions.
• Contamination
– similar to that of pollution
– implies making something unfit for a
particular use through the introduction of
undesirable materials
Terminology
• Toxic refers to materials (pollutants)
that are poisonous to people and other
living things.
– Toxicology is the science that studies
chemicals that are known to be or could
be toxic.
• Carcinogen is a particular kind of
toxin that increases the risk of cancer.
– Most feared and regulated toxins in our
society.
Terminology
• Additivity - A biologic response to
exposure to multiple substances that
equals the sum of responses of all the
individual substances added together
• Antagonism – A biologic response to
exposure to multiple substances that is
less than would be expected if the known
effects of the individual substances were
added together
Terminology
• Synergism
– The interaction of different substances
resulting in a total effect great than the sum
of the effects of the separate substances.
– E.g. sulfur dioxide and coal dust
Terminology
• Pollutants introduced into the
environment at:
• Point sources, such as smokestacks,
pipes discharging into waterways, stream
entering the ocean, or accidental spills.
The Clean Water Act specifically defines a
"point source" in section 502(14) of the
Act. That definition states:
Terminology
• The term "point source" means any
discernible, confined and discrete
conveyance, including but not limited to
any pipe, ditch, channel, tunnel, conduit,
well, discrete fissure, container, rolling
stock, concentrated animal feeding
operation, or vessel or other floating
craft, from which pollutants are or may
be discharged. This term does not include
agricultural storm water discharges and
return flows from irrigated agriculture.
Terminology
• Pollutants introduced into the
environment at:
– Non point sources (Area sources), which
are more diffused over the land and include
urban and agricultural runoff and mobile
sources such as automobile exhaust.
Nonpoint Source Pollution
• Nonpoint source (NPS) pollution, unlike
pollution from industrial and sewage
treatment plants, comes from many
diffuse sources. NPS pollution is caused
by rainfall or snowmelt moving over and
through the ground. As the runoff moves,
it picks up and carries away natural and
human-made pollutants, finally
depositing them into lakes, rivers,
wetlands, coastal waters, and even our
underground sources of drinking water.
Nonpoint Source Pollution
Nonpoint sources include:
• Excess fertilizers, herbicides, and insecticides from
agricultural lands and residential areas;
• Oil, grease, and toxic chemicals from urban runoff and
energy production;
• Sediment from improperly managed construction sites,
crop and forest lands, and eroding streambanks;
• Salt from irrigation practices and acid drainage from
abandoned mines;
• Bacteria and nutrients from livestock, pet wastes, and
faulty septic systems;
• Atmospheric deposition and hydromodification are also
sources of nonpoint source pollution.
Point Source or Nonpoint Source?
Why?
Measuring the Amount of
Pollution
• How the amount or concentration of a
particular pollutant or toxin present in the
environment is reported varies widely.
– E.g. waste water reported in millions of
gallons
– Emissions of nitrogen oxides reported in
tons per year
– Others given by a volume, mass of weight
• ppm, ppb, mg/kg or %
Practice
Suppose 17 grams of sucrose is
dissolved in 183 grams of water. What
is the concentration of sucrose in ppm?
17 X 1,000,000 = 170000 ppm
(17+183)
The solubility of AgCl is 0.008 grams/100
grams of water. What is this
concentration in ppm?
0.008 X 1000000 = 80 ppm
100
Infectious Agents
• Infectious disease
– Spread from the interactions between
individuals and food, water, air or
soil.
– Can travel globally via airplanes
– New diseases emerging and previous
ones reemerging
– Diseases that can be controlled by
manipulating the environment
• classified as environmental health
concerns
Environmentally
Transmitted Infectious
Diseases
• Legionellosis
– Occurs where air-conditioning systems have
been contaminated by disease-causing
organisms.
• Giardiasis
– a protozoan infection of the small intestine
spread via food, water, or person-to-person
contact.
• Salmonella
– a food-poisoning bacterial infection spread
via water or food.
Environmentally
Transmitted Infectious
Diseases
• Malaria
– a protozoan infection transmitted by
mosquitoes.
• Lyme disease
– Transmitted by ticks.
• Cryptosporidosis
– a protozoan infection transmitted via water
or person-to-person contact.
• Anthrax
– Bacterial infection spread by terrorist
activity.
Toxic Heavy Metals
• The major heavy metals that pose
health hazards to people and
ecosystems include:
– mercury, lead, cadmium, nickel, gold,
platinum, silver, bismuth, arsenic,
selenium, vanadium, chromium, and
thallium.
• Each may be found in soil and water not
contaminated by humans.
Toxic Heavy Metals
• Often have direct physiological
effects.
– Stored and incorporated in living
tissue
• Fatty body tissue
– Content in our bodies referred to as
body burden.
Toxic Pathways
• Chemical elements can become
concentrated
• Biomagnification- the increased concentration of a toxic
chemical the higher an animal is on the
food chain.
• Bioaccumulation– the accumulation or increase in
concentration of a substance in living
tissue of a particular organism.
– E.g. Cadmium, mercury
Minamata
By: Laurie Brier, Benny DeShazer, Miranda
Holmes, and Matthew Shelnutt.
The Town of Minamata
• Located on the coast of
the Yatsushiro Sea in
southwestern Japan.
• The village was very
poor.
– Mostly fishermen and
farmers.
• Villagers welcome
Chisso Corporation
http://www.jnto.go.jp/tourism/img/map/86.gif
Chisso Corporation
• Chisso = nitrogen
– Produced fertilizer
• 1907: Chisso Corp. builds
a fertilizer plant in the
Minamata.
• Job openings
• 1925: plant begins
dumping untreated
wastewater into
Minamata Bay
– Kills fish
– Fisherman Payoffs
http://www.japanfocus.org/images/592-3.jpg
Chisso Corporation
• 1932: Chisso plant begins to
produce acetaldehyde to be
used in the production of
plastic, perfume and drugs.
• Acetaldehyde is made from
acetylene and water with a
mercury catalyst.
• After WWII plastic
production boomed and
Chisso Corp. grew.
• By 1970: Chisso brought
Japan 60% of its income and
owned nearly 70% of the
land in Minamata.
http://www-personal.umich.edu/~tobin/Smith2.jpg
Bizarre Behavior in Animals
• Early 1950’s:
– Dead fish wash ashore
– Crows fall out of sky
– Suicidal dancing cats
• Mercury moves up the
food chain.
http://flickr.com/photos/tropicalrips/127535537/
Mid 1950’s: Behavior Seen in Humans
• Behaviors witnessed:
– Loss of motor control in
hands
– Violent tremors
– Swaggered walk
– Insanity
• “Cat-dancing” disease
• Nobody knew the cause
of the epidemic.
– Many hid for fear of
ridicule
http://www.hamline.edu/personal/amurphy01/es110/eswebsite/Proj
ectsSpring03/ebarker/Minamata%20Web%20Page.htm
Putting the Pieces Together
• 1956: Researchers at
Chisso Corp. Hospital
experiment on cats with
wastewater from the
Chisso plant.
• They warn Chisso corp.
• Chisso corp. redirects the
flow of wastewater to
avoid being caught.
– A larger geographical area
contaminated.
– Children born with
horrifying deformities.
http://www.nimd.go.jp/archives/english/tenji/a_corner/image/hasseimap.gif
Putting the Pieces Together
• 1968: Government ran
Public Health service traces
the contamination to the
Minamata Chisso plant.
• Government halts the
production of acetaldehyde
• 1972: Government
publically announces Chisso
Corp’s part in the Minamata
epidemic and orders Chisso
Corp to pay compensation
to the families that were
affected.
http://www.icett.or.jp/lpca_jp.nsf/505b1fe895fd2a8c492567ca000d587d/e
35dc782654b21d7492567ca000d8c50?OpenDocument
Centers for Disease Control and Prevention
The Aftermath
• 30-70 tons of methyl
mercury was dumped into
the Bay
• 10,000 people affected by
Minamata disease.
– 3,000 died
• Compensation has been
given to families as
recently as 1990.
– Highest compensation for
the disaster was just under
$3,000.
http://www.physorg.com/news110359851.html
Methylmercury :
In the Body
• Methylmercury exposure in
humans is from
consumption of fish, marine
mammals, and crustaceans
• 95% of fish-derived
methylmercury is absorbed
into the gastrointestinal
tract and distributed
throughout the body
– Highest in concentration in
hair
www.mercury.utah.gov/images/health_effects.jpg
Minamata Disease in the Nervous System
Areas in red show areas typically affected
by the presence of methylmercury in
the system . The lesions show
characteristic signs and symptoms in
Minamata disease.
1. Gait disturbance, loss of balance
(ataxia), speech disturbance
(Dysarthria)
2. Sight disturbance of peripheral areas in
the visual fields (constriction of visual
fields)
3. Stereo anesthesia (Disturbance of
sensation)
4. Muscle weakness, muscle cramp
(disturbance of movement)
5. Hardness of hearing (hearing
disturbance)
6. Disturbance of sense of pain, touch or
temperature (Disturbance of sensation)
National institute of Minamata Disease Archives
Symptoms of the Disease
• Mild
–
–
–
–
Ataxia
Muscle weakness
Narrowed field of vision
Hearing and speech
damage
• Severe cases cause
–
–
–
–
Insanity
Paralysis
Coma
Death
W. Eugene Smith
Tomoko Uemura in Her Bath
Minamata, 1972
More Symptoms
• A significant effect of
Minamata is the onset of
symptoms similar to
those of cerebral palsy
• Fetal Minamata Disease
– A pregnant mother ingests
toxic fish and the
methylmercury
concetrates inside the
placenta.
– Harms the fetus while the
mother is relatively
unaffected
http://picasaweb.google.com/jazzyv0504/SA
KURA#5065603192708172658
These are all children with congenital (fetal) Minamata Disease
due to intrauterine methyl mercury poisoning (Harda 1986).
Mercury: The Basics
• Mercury (Hg) is the only metal
that is liquid at room
temperature. It melts at
38.9oC and boils at 356.6oC.
• Mercury conducts electricity,
expands uniformly with
temperature and easily forms
alloys with other metals (called
amalgams).
– For these reasons, it is used in
many products found in homes
and schools.
Mercury Chemistry
• Mercury exists in three
oxidation states:
– Hg0 (elemental mercury).
– Hg22+ (mercurous).
– Hg2+ (mercuric).
• Mercurous and mercuric
form numerous inorganic
and organic chemical
compounds.
– Organic forms of mercury,
especially methyl mercury,
CH3Hg(II)X, where “X” is a
ligand (typically Cl- or OH-) are
the most toxic forms.
Uses of Mercury
• We use its unique properties to
conduct electricity, measure
temperature and pressure, act
as a biocide, preservative and
disinfectant and catalyze
reactions.
– It is the use of mercury in
catalysis that contributed to the
events in Minamata.
• Other uses include batteries,
pesticides, fungicides, dyes and
pigments, and the scientific
apparati.
Mercury in the Environment
• Upwards of 70% of the mercury in
the environment comes from
anthropogenic sources, including:
– Metal processing, waste
incineration, and coal-powered
plants.
• Natural sources include volcanoes,
natural mercury deposits, and
volatilization from the ocean.
• Estimates are that human sources
have nearly doubled or tripled the
amount of mercury in the
atmosphere.
The Aquatic Mercury Cycle
Cleaning up
• The Minamata Spill
– Dredging
• Other ways of cleaning mercury spill
Mercury-resistant bacteria, developed by researchers from
Inter American University of Puerto Rico, Bayamon Campus,
contained either the mouse gene for metallothionein or the
bacterial gene for polyphosphate kinase. Both strains of
bacteria were able to grow in very high concentrations
(120µM) of mercury, and when the bacteria containing
metallothionein were grown in a solution containing 24 times
the dose of mercury which would kill non-resistant bacteria,
they were able to remove more than 80% of it from the
solution in five days.
Minamata Cleanup
• What’s is Dredging?
– Underwater excavation
Minamata Cleanup
• Dredging
– Types
• Mechanical
• Hydraulic
• Airlift
Hydraulic
Mechanical
Airlift
Minamata Cleanup
• Disposal of Sediment
–
–
–
–
Landfills
Disposal facility
Ocean placement
Confined Disposal
Facilities (CDFs)
Recycling
Separation
U.S. Mercury Cleanups
•
•
•
•
Precipitation/ Co precipitation
Absorption treatment
Membrane Filtration
Biological treatment
Other ways of Clean Up
• Capping of Mercury – contaminated Sediments
w/ sand
• Inhibition of Mercury Methylation by Iron
Sulfides
• Immobilization of Aqueous Hg (II) by Iron
Sulfides
Experimental Research
•
•
•
•
Nanotechnology
Phytoremediation
Air Stripping
In Situ Thermal Desorption (ISTD)
Minamata Bay Today
• Eco Park of Minamata Bay has 2 purposes
– A stone memorial
– Landfill for Mercury
Questions???
Organic Compounds
• Organic compounds
– compounds of carbon produced
naturally by living organisms or
synthetically by human industrial
practices.
• Synthetic organic compounds
– Used in industrial processes, pest
control, pharmaceuticals, and food
additives.
– Over 20 million
Persistent Organic
Pollutants
• POPs may produce a hazard for
decades or hundreds of years.
– First produced when their harm was
not known
– Now banned or restricted
Persistent Organic
Pollutants
• POPs have several properties that
define them:
– They have a carbon-based molecular
structure, often containing highly reactive
chlorine.
– Most are synthetic chemicals.
– They do not easily break down in the
environment.
Persistent Organic
Pollutants
– They are polluting and toxic.
– They are soluble in fat and likely to
accumulate in living tissue.
– They occur in forms that allow them to be
transported by wind, water, and sediments
for long distances.
Dioxins
• Dioxins & incineration:
• A) history
• B) chemistry
• C) biology
• D) health threat
AIR EMISSIONS
CO2 + H2O
ACID GASES:
HCI, HF, SO2
NOx
TOXIC METALS:
Pb, Cd, Hg, As, Cr etc
COMPOUNDS:
PCB’s
PCDDs (DIOXINS)
PCDFs (FURANS)
NANO
PARTICLES
History
• 1960s, 1970s Most people hear of dioxins in
relation to use of Agent Orange in Vietnam
• 1949 - 1976 dioxins produced in industrial
accidents in plants making 2,4,5
Trichlorophenol. Most famous Seveso, Italy
in 1976.
• 1977 dioxins found in trash incinerator
emissions
• 1977 -’85 Engineers argue that dioxin
problem solved by running incinerator
furnaces at high temps. They were wrong
• 1985 - find dioxins formed after the furnace.
Dioxin 1980s - 1990s
• Biggest source of dioxin is from food,
particularly animal fat.
• Biggest source of dioxin entering food
chains = combustion esp. of municipal
waste.
• Medical, municipal and hazardous waste
incineration, backyard burning (PVC),
Fires (PVC), copper recycling (PVC),
metal smelting
• 1990’s better dioxin control from
incineration. Many plants retrofitted and
older plants closed down.
DIOXINS
The chemical structures
Dioxin like compounds
(DLC)
• 3 families
• PCBs
• PCDFs (furans)
• PCDDs (dioxins)
Polychlorinated biphenyls
One of 209 PCBS
PCBs = a family of compounds in which
chlorine atoms are substituted for hydrogen
at 1 to 10 positions of BIPHENYL .
Furans (or PCDFs) have an oxygen atom forming
a five membered ring (the furan) between the two
benzenes of PCBs. There are 135 furans.
Furans (or PCDFs)
Furans (or PCDFs) have an oxygen atom forming
a five membered ring (the furan) between the two
benzenes of PCBs. There are 135 furans.
2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN
Dioxins (or PCDDs) have two oxygen atoms
linking the two benzene rings, forming the
dioxin ring. There are 75 dioxins.
Dioxins (or PCDDs)
2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN
Dioxins (or PCDDs) have two oxygen atoms
linking the two benzene rings, forming the
dioxin ring. There are 75 dioxins.
There are 17 extremely toxic dioxins and furans. They
have chlorine at the 2,3,7 and 8 positions:
7 Dioxins
and
10 Furans
The biology of Dioxins
Dioxin
Or
Dioxin-like
Compound
(DLC)
CELL
Ah receptor
Arnt
protein
Complex
With
Changed shape
DNA
NUCLEUS
Dioxins
do not cause
mutations
But
switch on genes
Switching on a gene
means producing a
specific messenger RNA
which codes for a
specific protein
messenger RNA
travels to the
ribosome
(= protein
factory)
In the ribosome
the messenger RNA
directs the
production of a
specific protein
New
protein
New
protein
New protein modifies the activity of the cell and may lead
to cancers and endocrine disorders esp. in developing
Animals.
Dioxins - major health
concerns
• Dioxins accumulate in animal fat. One liter of
cows’ milk gives the same dose of dioxin as
breathing air next to the cows for EIGHT MONTHS
.
• In one day a grazing cow puts as much dioxin
into its body as a human being would get in 14
years of breathing!
• Dioxins steadily accumulate in human body fat.
The man cannot get rid of them BUT A woman
can…
• …by having a baby!
• Thus the highest dose of dioxin goes to the fetus
and then to the new born infant via
breastfeeding…
Dioxins interfere with fetal and
infant devlopment
• Dioxins act like fat soluble hormones
• Disrupt at least six different hormonal
systems.
WE WANT DIOXIN
OUT OF OUR BABIES!
Institute of Medicine, 2003
• Fetuses and breastfeeding infants
may be at particular risk from
exposure to dioxin like compounds
(DLCs) due to their potential to
cause adverse neurodevelopmental,
neurobehavioral, and immune
system effects in developing
systems…
Institute of Medicine, 2003
• …The committee recommends that
the government place a high public
health priority on reducing DLC
intakes by girls and young women in
the years well before pregnancy is
likely to occur.
• (by) Substituting low-fat or skim
milk, for whole milk, (and)… foods
lower in animal fat…
WE WANT DIOXIN
OUT OF OUR FOOD!
Do not build incinerators
within 50 km of food
production - particularly
grazing animals
Promoters say that
modern incinerators have
solved the dioxin
problem, but have they?
• When PVC was fed into the high-temperature
melter, a significant quantity of PCDD/Fs,
cadmium and lead was emitted.
• Wet scrubbing with rapid quenching, as well
as a low temperature two-step fine filtration,
or both of them together cannot effectively
control the volatile metal species and gasphase PCDD/Fs.
• The removal of PVC from the feed waste
stream must also be effective to reduce the
emissions of the PCDD/Fs, cadmium and lead
species.
While modern incinerators
have reduced dioxin
emissions
there is no real
accountability
in most countries
YOU NEED THREE THINGS TO PROTECT THE
PUBLIC FROM TOXIC EMISSIONS.
YOU NEED THREE THINGS TO PROTECT THE
PUBLIC FROM TOXIC EMISSIONS.
STRONG
REGULATIONS
YOU NEED THREE THINGS TO PROTECT THE
PUBLIC FROM TOXIC EMISSIONS.
STRONG
REGULATIONS
ADEQUATE
MONITORING
YOU NEED THREE THINGS TO PROTECT THE
PUBLIC FROM TOXIC EMISSIONS.
STRONG
REGULATIONS
ADEQUATE
MONITORING
TOUGH
ENFORCEMENT
YOU NEED THREE THINGS TO PROTECT THE
PUBLIC FROM TOXIC EMISSIONS.
STRONG
REGULATIONS
ADEQUATE
MONITORING
TOUGH
ENFORCEMENT
IF ANY LINK IS WEAK THE PUBLIC IS NOT PROTECTED
Hormonally Active Agents
• HAA are also POPs.
• Have potential to cause
developmental and reproductive
abnormalities in animals, including
humans.
– Include a wide variety of chemicals,
herbicides, pesticides, phthalates,
and PCBs
Hormonally Active Agents
• Evidence in support of hypothesis
– Alligator populations in Florida exposed to
DDT have genital abnormalities, low egg
production and reduced penis size.
– Major disorders studied in wildlife have
centered on abnormalities including
• thinning of eggshells of birds, decline in
populations of various animals and birds,
reduced viability of offspring, and changes in
sexual behavior.
Hormonally Active Agents
• In humans
– HAAs may be linked to breast cancer
– PCBs and neurological behavior
– Phthalates (used as plastic softeners and are
responsible for that new car smell, which becomes
especially pungent after the car has been sitting in
the sun for a few hours, is partly the pungent odor
of phthalates volatilizing from a hot plastic
dashboard. In the evening's cool they then condense
out of the inside air of the car to form an oily coating
on the inside of the windshield.
– Endocrine and hormone disruption
Endocrine System
• One of two main systems that
regulate and control growth ,
development and reproduction.
• Composed of a group of hormone
secreting glands
– Thyroid, pancreas, pituitary, ovaries
and testes.
– Hormones transported by blood
stream, act as chemical messengers.
Hormonally Active Agents
• The National Academy of Sciences
– recommends that there should be
continued monitoring of wildlife and human
populations for abnormal development and
reproduction.
Radiation
• Nuclear radiation is linked to
serious health problems
– Including cancer
Thermal Pollution
• Occurs when heat released into
water or air produces undesirable
effects.
– Also called heat pollution
– Sudden acute event or long term,
chronic release
– Heated water released into rivers
changes temp and dissolved oxygen
content
• Thereby changing river’s species
composition
Thermal Pollution
• Heating river water changes
natural conditions and disturbs the
ecosystem
– Fish spawning cycles may be
disrupted
– Fish may have heightened
susceptibility to disease.
– Physical stress on fish
– Easier pray
– Change in type and availability of
food
Thermal Pollution
• Solutions to chronic thermal
heating
– Release of heat into air in cooling
towers
– Artificial lagoons
– Used to heat buildings
Particulates
• Small particles of dust released
into the atmosphere by many
natural processes and human
activities.
– Modern farming
– Burning oil and coal
– Dust storms
– Volcanic eruptions
Asbestos
• A term for several minerals that take the form
of small, elongated particle or fibers.
– Use contributed to fire prevention
– Insulation
• Inhalation leads to asbestosis and cancer
• 95% of asbestos now in use in US chrysolite
(white asbestos).
– Not particularly harmful
• Another type crocidolite (blue asbestos)
– Exposure can be very hazardous
Electromagnetic Fields
• EMFs part of everyday urban life
– electric motors, transmission lines
and appliances
– Controversy as to whether they pose
a health risk
– Children may be at greater risk
– Studies have shown that associations
between CA and exposure to EMFs is
not strong and not statistically
significant.
Noise Pollution
• Unwanted sound
• Sound is a form of energy that
travels as waves
– We hear sounds when waves vibrate
our eardrum
– Loudness a measure of intensity of
energy
– Measured in units of decibels
Noise Pollution
• Environmental effects of noise depend
on
–
–
–
–
–
Energy
Pitch
Frequency
Time pattern
Length of exposure
• Very loud noise can cause pain
• Any sound above 80dB can cause
hearing loss
– Rock concert 110dB
• Constant high noise causes stress
Voluntary Exposure
• Sometimes referred to as exposure
to personal pollutants.
– Tobacco
• 30% of cancers tied to smoking
– Alcohol and other drugs
• ½ of all deaths in automobiles accidents
tied to alcohol use by drivers
• Violent crimes, overdoses, chronic
alcoholism
General Effect s of
Pollutants
• Almost every part of the human
body is affected by one pollutant
or another.
Concept of Dose and
Response
• Five centuries ago, the physician
and alchemist Paracelsus wrote
that “everything is poisonous, yet
nothing is poisonous.”
• For Example
– Selenium required in small amounts
by living things
– May be toxic in high concentrations
Concept of Dose and
Response
• The effect of a chemical on an
individual depends on the dose.
– Dose response
– Dose dependency can be represented
by a generalized dose response
curve.
Concept of Dose and
Response
• Doses that are beneficial, harmful, or
lethal may differ widely for different
organisms and are difficult to
characterize.
• E.g. fluoride and dental health
– Fluorine forms fluoride compounds that
prevent tooth decay and promote healthy
bone structure.
– Toxic effects are noticed at concentrations
of 6-7 ppm
Dose-Response Curve
• How individuals will response to a
chemical not know.
• Instead predictions made about
how a percentage of the
population will respond to a
specific dose.
• Dose at which 50% of the
population dies
– Lethal dose 50, LD-50
Dose-Response Curve
• The ED-50 (effective dose 50%) is
the dose that causes an effect in
50% of the population of observed
subjects.
– E.g. ED-50 of aspirin would be the
dose that relieves headaches in 50%
of the people.
Dose-Response Curve
• The TD-50 (toxic dose 50%) is
defined as the dose that is toxic to
50% of the population.
– Often used to indicate responses such
as reduced enzyme activity,
decreased reproductive success, or
onset of specific symptoms.
Dose-Response Curve
• For a particular chemical, there may be
a whole family of dose–response
curves.
– Which dose is of interest depends on what
is being evaluated.
– Killing insects vs. pesticide residue
– Overlap between the therapeutic dose (ED)
and the toxic dose (TD)
– Measure of the relative safety of a particular
drug is the therapeutic index
• Defined as the ratio of the LD-50 to the ED-50.
• The greater the therapeutic index, the safer the
drug.
Threshold effects
• Threshold is a level below which no
effect occurs and above which effects
begin to occur.
– If a threshold exists, then a concentration
below the threshold is safe.
– If there is no threshold dose, then even the
smallest amount has some negative toxic
effect.
• A problem in evaluating thresholds for
toxic pollutants is that it is difficult to
account for synergistic effects.
Ecological Gradients
• Changes in vegetation with
distance from a toxic source define
the ecological gradient.
– Weedy species adapted to harsh
conditions may be closer
– Farther away trees and shrubs
Tolerance
• The ability to resist or withstand stress
resulting from exposure to a pollutant or
harmful condition.
– Result from behavioral, physiological, or
genetic adaptation.
• Behavioral tolerance- change in
behavior
– Learning to avoid traps
Tolerance
• Physiological tolerance- the body
of an individual adjusts to tolerate
a higher level of pollutant.
– Many mechanisms including
detoxification
• the toxic chemical is converted to a
nontoxic form
– Internal transport of the toxin to a
part of the body where it is not
harmful, such as fat cells.
Tolerance
• Genetic tolerance- (adaptation)
when some individuals in a
population are naturally more
resistant to a toxin than others.
– Strains of mosquitoes resistance to
DDT
– Antibiotic resistance
Acute and Chronic Effects
• Acute effect is one that occurs
soon after exposure.
– Usually to large amounts of a
pollutant
• Chronic effect takes place over a
long period
– Often as a result of exposure to low
levels of pollutant
Risk Assessment
• The process of determining
potential adverse environmental
health effects to people exposed to
pollutants and potentially toxic
materials.
Risk Assessment
• Such an assessment generally includes
four steps:
–
–
–
–
Identification of the hazard.
Dose–response assessment.
Exposure assessment.
Risk characterization.
• Risk assessment is difficult, costly, and
controversial.
• Risk management integrates the
assessment of risk with technical, legal,
political, social, and economic issues.