Environmental Science
Unit 4 - Risk, Toxicology,
& Human Health
(STE 7th ed. Chapter 11)
Where are we going?
- Types of hazards
- Toxicology
- Chemical hazards
- Biological hazards
- Risk Analysis
estimating risk, major risks, issues
Types of Hazards
•
Risk is a measure of the possibility of experiencing a hazard that can
cause harm
– expressed as a probability; 1 in 200, 1 in 1000 etc.
e.g. risk of death from flying in US 1 in 7,000,000
– risk assessment involves estimation of the probability of harm to
human health, society, or the environment that may result from
exposure to specific hazards
– risk management involves the decision to reduce a risk and the
costs associated
Types of Hazards
Identify the (i) Risk, (ii) Hazard and (iii) Risk Management
NYT Jan 29th 1995
Types of Hazards
Risk as a Probability
NYT Jan 29th 1995
NOVA
How Risky is Flying?
NOVA:
Deadliest
Plane Crash
NOVA
How Risky is Flying?
NOVA:
Deadliest
Plane Crash
Types of Hazards
Major Hazards
• cultural hazards
unsafe working conditions, smoking, poor diet, drugs, drinking, driving,
flying, criminal assault, poverty;
• chemical hazards
harmful chemicals in air, water, soil, & food;
• physical hazards
noise, fire, tornadoes, hurricanes, earthquakes, volcanic eruptions, floods, &
ionizing radiation;
• biological hazards
pathogens, pollen & other allergens, & animals such as bees & poisonous
snakes
Causes of Death
Annual Deaths
3 x 400
passenger jets
crashing every
day
WHO estimates
80 x 106 deaths 1950-2000
3 x more than all wars of 20th
century
US deaths in 2003
+ many more
Movie
The Realities of Risk (13 of 29 mins)
View the following movie:
http://vega.org.uk/video/programme/5
(part of the series http://www.open2.net/nextbigthing/
Questions:
(i) What is risk bootstrapping?
(ii) Why does the scientist think it was ‘daft’ to ban the pesticide ‘alar’?
Case Study:
A Black Day in Bhopal, India
•
The world’s worst industrial accident:
1984 pesticide plant, Bhopal India.
– An explosion at Union Carbide
pesticide plant in an underground
storage tank released a large
quantity of highly toxic methyl
isocyanate (MIC) gas.
– 15,000-22,000 people died
– Indian officials claim that simple
upgrades could have prevented the
tragedy.
Toxicology
•
study of the adverse effects of chemicals on health
–
toxicity: measure of how harmful a substance is;
depends on:
–
dose: amount of a potentially harmful substance ingested,
inhaled, or absorbed through the skin;
Also: frequency of exposure, age, effectiveness of detox
systems, genetics
–
response: resulting type & amount of damage to health
may be acute or chronic
Toxicology
The dose makes the poison
Any chemical be it natural or synthetic can be harmful
Should we be concerned?
…traces of synthetic chemicals in our environment
•
•
Lack of data
Effects difficult to determine
Poor diet + pollution = brain damage
Which is major factor?
•
•
Life expectancy has increased
Lower levels and new contaminants are
being detected due to new technology
Misconception
•
Misconception that all natural chemicals are safe and all sythentics are
bad
e.g. fruit seeds and pips form cyanide in the stomach, green potatoes,
naturally occuring pesticides, mould/fungi on food
Toxicology
Toxicity of Chemicals
• Animal testing, case and epidemiological reports
• generally defined by LD50 – amount in a dose that kills 50 %
of population in 14 days
• poison: legally defined as a chemical that has an LD50 of 50
milligrams or less per kilogram of body weight
Table 17–1
Toxicity
Rating
super toxic
extremely toxic
very toxic
toxic
moderately
toxic
slightly toxic
Average Lethal
LD50
Dose
Examples
< 0.01 less than 1 drop nerve gases, botulism,
mushroom toxins, dioxin
<5
less than 7
potassium cyanide, heroin,
drops
atropine, parathion, nicotine
5–50
7 drops to 1 tsp mercury salts, morphine,
codeine
50–500 1 teaspoon to 1 lead salts, DDT, sodium
ounce
hydroxide, fluoride, sulfuric
acid, caffeine, carbon
tetrachloride
500–
1 ounce to 1 methyl alcohol, ether,
5,000
pint
pehobarbital, amphetamines,
kerosine, aspirin
5,000– 1 pint to 1 quart ethyl alcohol, lysol, soaps
15,000
Toxicology
Responses
•
•
Acute toxicity:
– Sudden and severe exposure
– Rapid onset of symptoms
Chronic toxicity:
– Continuous, long-term exposure
– Relatively low dose
– Cancer, birth defects, neurological damage
Same chemical may
show both effects
e.g. skin irritation vs.
cancer
Toxicology
Dose-Response
•
•
Acute toxicity tests
design:
– Controls (no dose) &
treatments (low to high
dose)
– test organism
(usually rats or mice)
– replicates (usually 60–200
animals total)
– period (often 14 days)
2-5 years, $200,000-$2 million
High doses are used to reduce no.
subjects and increase speed of test
- Extrapolated down to low doses
Dose–Response Curves
Any dosage is harmful
(Assumed in most cases)
Lower limit to harmful dose
Question
If a dose of 0.1 μg is sufficient to kill a mouse, what mass would be fatal
to you?
Ratio mass human : mouse = 200 : 1
Mass that would kill you = 200 x 0.1 μg = 20 μg
What average level of substance would have to be present in drinking
water for you to receive a fatal dose in one week?
2 L water d-1 x 7 d w-1 = 14L
For fatal dose 20 μg / 14 L = 1 μg L-1 = 1 ppb
Toxicology
•
Complications
– Different physiology
– Synergestic effects –
difficult and expensive to
test for 1, no. tests multiply
when consider more than 1
•
Because of complexity in
determining toxicity allowed
exposure levels are set 1001000 x below harmful levels
Toxicology
Estimating human
exposure to
chemicals and their
effects is very difficult
because of the many
and often poorly
understood variables
involved.
Toxicology
• Children are more susceptible to the effects of toxic substances
because:
– Children breathe more air, drink more water, and eat more
food per unit of body weight than adults.
– They are exposed to toxins when they put their fingers or
other objects in their mouths.
– Children usually have less well-developed immune systems
and detoxification processes than adults
Toxicology
• The U.S. Environmental Protection Agency proposed that
regulators should assume children have 10 times the exposure
risk of adults to cancer-causing chemicals
• Some health scientists contend that regulators should assume a
risk 100 times that of adults
Background
•
•
•
•
Birth defects due to exposure to
synthetic chemicals
Toxicity to mammals and birds
Carcinogenic effects
Xenoestrogenic effects
•Gt. Lakes cormorant
with crossed bill
ES&T Article
Chemical Hazards
Toxic chemicals
(kill)
Hazardous chemicals
(harm)
Chemical Hazards
Toxic Chemicals
Temporary or Permanent harm or death:
• mutagens: cause random mutations (changes in the DNA)
e.g. nitrous acid, UV, γ, α radiation
• teratogens: cause birth defects
e.g., alcohol, PCBs, steroid hormones, heavy metals
• neurotoxins: damage nervous system
e.g., DDT, alcohol, heavy metals
• carcinogens: cause cancer
- over 100 types
e.g. benzene, dioxin, radionuclides, asbestos
http://en.wikipedia.org/wiki/International_Agency_for_Research_on_Cancer
Hazardous Chemicals
cause harm in various ways
• flammable or explosive
(e.g., gasoline);
• irritating or damaging to skin or lungs
(e.g., strong acids or alkalis)
• interfering with or preventing oxygen uptake & distribution
(e.g., carbon monoxide, CO);
• inducing allergic reactions of the immune system (allergens)
Dioxin Incidents
Times Beach, Missouri
NYT 121682
Dioxin Incidents
Times Beach, Missouri
1972-76
dirt roads were sprayed with waste oil containing
super concentrated dioxin from Agent Orange
manufacture
1992 - Town was demolished
1997 - 265,000 tons of soil was incinerated on site
Now Route 66 State Park
Shown in History Channel Modern Marvels #20
Effects at Low Doses
Long-term exposure to some chemicals at low doses may
disrupt the body’s:
• Immune system: specialized cells and tissues that protect
the body against disease and harmful substances.
• Nervous system: brain, spinal cord, and peripheral
nerves.
• Endocrine system: complex network of glands that
release minute amounts of hormones into the
bloodstream.
Hormone Disrupters
• hormones: molecules that act as messengers to regulate various
bodily processes, including reproduction, growth, & development
(endocrine system)
• hormone disrupters: interfere with hormone function
• so far 51 chemicals shown to act as hormone disrupters on
wildlife, laboratory animals, & humans
- e.g., dioxins, certain PCBs, various chemicals in plastics,
some pesticides, lead & mercury
• 1997 study shows that sperm count of men in U.S. & Europe has
declined 50%
Hormone Disrupters
Molecules of certain synthetic chemicals have
shapes similar to those of natural hormones and
can adversely affect the endocrine system
Biomagnification
A chemical whose concentration
increases along a food chain is said
to be biomagnified
•DDT concentration in Lake Ontario Trout
Biomagnification results from a
sequence of bioaccumulation steps
Biomagnification
when a chemical becomes concentrated in specific organs
or tissues
e.g., DDT, dioxin, PCBs accumulates in fatty tissues
Known as persistent organic pollution (POP)
contributing factors:
• organic chemical (like dissolves like)
• high persistence
• not easily broken down or excreted
Health Effects
Effects in Utero
•
Exposure to low levels
results in impaired
intellectual development
NYT, September 12th 1998
Health Effects
Dioxins, Furans and PCBs in Food
•95% of human exposure to
•dioxins and furans is from
•the presence of these
•compounds from food
•Fresh water fish has the
•highest level of PCBs
•Schecter et al., 1997
NYT July 2nd 2003
Why do we know so little?
• Under existing laws, most chemicals are considered innocent
until proven guilty, and estimating their toxicity is difficult,
uncertain, and expensive.
– Federal and state governments do not regulate about 99.5%
of the commercially used chemicals in the U.S.
– Only 10% of 80,000 chemicals have been tested for toxicity
– Chemicals are considered innnocent until proven guilty
Pollution Prevention
“better safe than sorry”
• Some scientists and health officials say that preliminary but not
conclusive evidence that a chemical causes significant harm
should spur preventive action (precautionary principle)
• Manufacturers contend that wide-spread application of the
precautionary principle would make it too expensive to introduce
new chemicals and technologies
Pollution and Cancer
• Bruce Ames believes that the focus on man-made chemicals as
causes of cancer is a distraction from the real threats of smoking
and diet
• Media:
http://www.bruceames.org/bnamedia.html
Environmental Testing
•
Experiments with test animals are used to determine how carcinogenic
a compound is, take many years
•
The simple Ames test can be used fairly rapidly to distinguish
compounds likely to be human carcinogens
Biological Hazards
nontransmissible diseases
• cardiovascular disorders, cancers, emphysema, & malnutrition;
transmissible (infectious) diseases
• caused by bacteria, viruses, protozoa, or parasites
• colds, flus, hepatitis, sexually transmitted diseases, malaria
• many transmissible diseases spreading over broad geographic areas
- Lyme disease (bacteria)
- Giardia (protozoa)
Biological Hazards
Infectious disease pathways
Transmissible Diseases
WHO estimates that each
year the world’s seven
deadliest infections kill 13.6
million people – most of them
the poor in developing
countries
Case Study: Growing Germ Resistance to
Antibiotics
•
Rabidly producing infectious bacteria ‘superbugs’ (e.g. MRSA) are
becoming genetically resistant to widely used antibiotics due to:
– Genetic resistance: Antibiotic resistance is a consequence of
evolution via natural selection
– Overuse of antibiotics:
(i) A 2000 study found that half of the antibiotics used to treat
humans were prescribed unnecessarily
(ii) over 70% of all antibiotics used in US given to animals in the
absence of disease
Case Study: The Growing Global Threat
from Tuberculosis
•
•
The highly infectious tuberculosis (TB) kills 1.7 million people per year
and could kill 25 million people 2020.
Recent increases in TB are due to:
– Lack of TB screening and control programs especially in developing
countries due to expenses
– Genetic resistance to the most effective antibiotics
Viral Diseases
•
Flu, HIV, and hepatitis B viruses infect and kill many more people each
year then highly publicized West Nile and SARS viruses
– The influenza virus is the biggest killer virus worldwide
– Pigs, chickens, ducks, and geese are the major reservoirs of flu. As
they move from one species to another, they can mutate and
exchange genetic material with other viruses
•
HIV is the second biggest killer virus worldwide. Five major priorities to
slow the spread of the disease are:
– Quickly reduce the number of new infections to prevent further
spread
– Concentrate on groups in a society that are likely to spread the
disease
– Provide free HIV testing and pressure people to get tested.
– Implement educational programs
– Provide free or low-cost drugs to slow disease progress
Case Study:
Malaria kills about
2 million – Death by Mosquito
Malaria
people per year and has
probably killed more than all
of the wars ever fought
Case Study:
Malaria – Death by Mosquito
• Spraying insides of homes with low concentrations of the
pesticide DDT greatly reduces the number of malaria cases.
– Under international treaty enacted in 2002, DDT is being
phased out in developing countries
http://www.doc3d.com/malaria/malaria_WMV.html
http://www.learner.org/channel/courses/biology/units/infect/images.html
Bioterrorism
• Possible targets: air, water, and food
•
Inexpensive
• Fairly easy to produce biological agents
• Recombinant DNA techniques
Risk Analysis
Scientists have developed
ways to evaluate and
compare risks, decide how
much risk is acceptable, and
find affordable ways to
reduce it.
Risk Assessment
To perform risk assessment it is important to know:
•
Hazard evaluation information (acute, cancer ???)
•
Quantitative dose-response information
•
An estimate of the potential human exposure to the chemical
The highest dose at which no observable effects level is called NOEL
(expressed in terms of mg kg-1 body weight day-1)
To determine the threshold level for the most sensitive members of the human
population, EPA uses Toxicity reference dose or RfD.
(RfD is also referred as Acceptable Daily Intake or ADI)
RfD (or ADI) = NOEL/100
(divide by safety factor of 100)
If NOEL for a chemical is 0.01 mg/kg/day, the ADI or RfD for a 80 kg man
would be (0.01 mg/kg/day /100) x 80 kg = 0.008 mg
• Estimating risks from using many technologies is difficult due
to unpredictability of human behavior, chance, and sabotage.
• Reliability of a system is multiplicative:
– If a nuclear power plant is 95% reliable and human
reliability is 75%, then the overall reliability is (0.95 X 0.75 =
0.71) 71%.
RISK ANALYSIS
• Annual deaths in
the U.S. from
tobacco use and
other causes in
2003
RISK ANALYSIS
• Number of deaths per year in the world from various
causes. Parentheses show deaths in terms of the
number of fully loaded 400-passenger jumbo jets
crashing every day of the year with no survivors.
Perceiving Risk
• Most individuals evaluate the relative risk they face based on:
– Degree of control
– Fear of unknown
– Whether we voluntarily take the risk
– Whether risk is catastrophic
– Unfair distribution of risk
• Sometimes misleading information, denial, and irrational fears
can cloud judgment
RISK
ANALYSIS
• Comparisons of
risks people face
expressed in
terms of shorter
average life span.
Becoming Better at Risk Analysis
• We can carefully evaluate
or tune out of the barrage
of bad news covered in
the media, compare risks,
and concentrate on
reducing personal risks
over which we have some
control