chapter 19 risk, toxicology and human health. risk risk: probability of suffering harm from a hazard...
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Chapter 19
Risk, Toxicology and Human Health
Risk
Risk: probability of suffering harm from a hazard- values range from: 0 ----> 1.0
can’t will happen happen
Risk Assessment: use of data, hypotheses and models to estimate risk caused by certain hazards
Risk Management: how serious? how much should it be reduced? how to reduce? how much to spend?
© 2004 Brooks/Cole – Thomson Learning
Verysensitive
Majorityof population
Veryinsensitive
0 20 40 60 80
Dose (hypothetical units)
Nu
mb
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f in
div
idu
als
affe
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Figure 19-3Page 411
4 Types of hazards
1) cultural hazards (unsafe working conditions, poor diet, smoking, drugs)
2) chemical hazards (in air,water, soil, food)
3) physical hazards (noise, fire, floods, ionizing radiation)
4) biological hazards (pathogens, allergens, snakes)
5) Lifestyle choices
Nontransmissible diseases
not caused by living organism
can’t spread from person to person
e.g. diabetes
Transmissible diseases caused by living organisms Bacterium, virus, protozoan, or parasite = pathogen 1) vectors: nonhuman carriers 2) bacterium: one celled microorganism 3) virus: noncellular, infectious agent, a strand of nucleic acid (either DNA or RNA) wrapped in a protein coat virus must invade host cell and take over cell’s DNA to make more viruses 80% of all illnesses in developing countries are caused by waterborne
infectious diseases e.g. diarrhea, hepatitis, cholera Note: when bacteria are treated with penicillin, survivors have mutant
genes that make them immune to medication---> natural selection Epidemiological transition: industrialized, less infectuous, more chronic
Tuberculosis
• Infects 9.2 m million per year.
• Kills 1.7 million per year.
• Bacterium spreads by airborne droplets
(coughing, talking)
• Half of infected people don’t know they are
• Most strains are genetically resistant to almost all previously effective antibiotics
Viral Diseases e.g. flu, HIV, hepatitis B, ebola, rabies From 1918-1919, flu epidemic killed 20-50
million people worlwide, 250,00 to 500,000 in US
(massive epidemic = pandemic)West Nile virus is transmitted by mosquito biteWest Nile, SARS, and Avian flu have moved
from animals to humans (Lyme Disease is bacterial disease spread from
deer and mice to humans, tick is vector)
Viral Diseases
Once a viral infection starts, it is harder to fight than bacteria or protozoan infections
1) antibiotics are useless and increases resistance of bacteria
2) preventative vaccines are the only effective weapon
AIDS
• Due to AIDS, life expectancy among 700 million in sub-Saharan Africa: 62-->42 years
• 2nd biggest viral killer (kills 2.1 mil/year)• Expensive drug cocktail ($25k/yr) extends life
tens of years• Priorities to slow spread: focus on high risk group
(IV drug users), research, education program for children, free testing, provide low cost drugs to slow progress
Malaria
• 40% of world population lives in regions where malaria is present
• Symptoms: chills, weakness, anemia• Kills about 1 million people per year• Spread by: anopheles mosquito bites person infected
with plasmodium parasite (type of protozoa), mosquito later bites uninfected person, spreading disease
• Parasite invades red blood cells ---> decreases body’s ability to transport O2 (anemia) ---> lower resistance
Malaria
• Spread of malaria was cut by draining swamps, spraying with insecticide, treating parasite with drugs
• Since 1970, disease has come back, mosquito became resistant to insecticides and parasite became resistant to drugs
• Spread is increasing because irrigation and hydropower has led to more breeding places, global warming has led to increased range
• In 2006, the WHO supported use of DDT for malaria control
Chemical Hazards
• Toxic Chemicals can cause temporary or permanent harm or death to
humans and animals EPA’s top five most toxic: arsenic, lead, mercury,
vinyl chloride (PVC), and PCBs• Hazardous Chemicals flammable or explosive irritating or damaging to skin or lungs (e.g. oven
cleaner) interfere with oxygen uptake (e.g. CO) induce allergic reactions of immune system
(allergens)
Chemical Hazards
Carcinogens
chemicals, radiation or viruses that cause growth of malignant tumors
examples include: PCBs, radon, UV radiation, chemicals in tobacco smoke, X-rays, vinyl chloride
cancer can be spread by metastasis: malignant cells break off from tumors and travel in body fluids to other parts
Chemical Hazards
Mutagens
chemicals or radiation that causes mutations in DNA
if mutation occurs in reproductive cell, affects future generations
may cause tumors in exposed person
Teratogens
chemicals, radiation or viruses that cause birth defects while embryo is growing (especially first 3 months) e.g. alcohol, PCB’s, thalidomide (sleeping pill, never approved in US), mercury, etc
PCBs
• b/w 1929 and 1977 used in transformers and capacitors (common in railroad yards)
• Causes cancer, learning disability
• Fat soluble so can be biomagnified
• Stable so persists in environment, mat travel great distances
Immune System
specialized cells and tissues that protect body against disease and harmful substances
2 levels of defense 1) antibodies detect and mark invaders for other immune cells to
attack 2) cellular defenses (e.g. T-cells) kill invaders
Pesticides can suppress human immune system
Neurotoxins can attack nerve cells (neurons)e.g. methyl mercury, DDT, PCB’s, dioxins
Mercury
• Teratogen and neurotoxin
• 1/3 naturally occurring
• 2/3 human caused: burning coal, waste incineration, fluorescent bulbs
• Bacteria can convert to methyl mercury which is fat soluble so can be biomagnified
• High levels found high on food chain (tuna)
Endocrine system
set of glands that release hormones into the bloodstream
1) hormones control sexual reproduction, growth, behavior, mix of estrogens and androgens determines sex
2) hormones (key and lock) connect with receptor molecule and move onto nucleus to execute message
Hormone Disrupters (human-made chemicals,DDT, PCBs)
1) hormone mimics ---> attack estrogen receptor molecules
2) hormone blockers ---> prevent androgen from attaching to receptor molecules
3) thyroid disrupters cause growth, brain, weight, behavior disorders
4) more than 60 chemicals (HAAs) are identified
e.g. dioxins (chlorinated hydrocarbons) are produced when chlorine compounds are incinerated (found in Agent Orange, defoliant used in Vietnam)
e.g. PCB’s, pesticides, lead, mercury, bisphenol A (found in plastic water bottles and baby bottles: brain damage on test animals)
Toxicology
study of health affects caused by chemicals
1) toxicity: how harmful a chemical is
2) Detoxification system: liver, kidney, etc
2) dose: amount of substance or radiation taken into body [acute (one dose), chronic (lifetime of doses)]
3) response: type and amount of damage to health
a) acute effect: immediate, rapid reaction to dose
b) chronic: permanent or long lasting result
Bioaccumulation
(typically occurs in organisms low on food chain)
a) toxins accumulate in fat cells over time
b) biological half-life: time required for 1/2 of chemical to be removed
c) water soluble toxins pass through in urine
Biomagnification
(high on food chain)
a) each consumer ingests toxins accumulated by each organism lower on the food chain
e.g. 10 minnows eat toxin. small fish eats 10 minnows. big fish eats 10 small fish. human eats big fish and the equivalent of 1000 minnows worth of toxin.
DDT ---> zooplankton ---> insects ---> spiders ---> mice ---> falcon
DDT in fish-eatingbirds (ospreys)
25 ppm
DDT in largefish (needle fish)2 ppm
DDT in smallfish (minnows)0.5 ppm
DDT inzooplankton0.04 ppm
DDT in water0.000003 ppm,Or 3 ppt
Figure 19-4Page 411
Dose
synergistic effects (antagonistic effects)
e.g. NO2, O3 react synergistically with allergens
LD50 dose required to kill 50% of test population
a) poison: chemical with an LD50 of 50 mg or less per kg of body weight
EPA lists top 5 toxic substances:
arsenic, lead, mercury, vinyl chloride (PVC), PCBs
Methods to determine toxicity
(public health threat)
1) case reports (anecdotal info on rxn to chemical)
2) lab study (done on test animals)
a) metabolites: products of body’s rxn to chemical
3) epidemiology
a) study of human populations exposed to chemicals or diseases
b)why do some get sick, others don’t
Dose-response curve
Shows effects of various doses of a toxic agent on a group of test organisms
• Requires a controlled experiment (test group vs control group)
• To save time and money, high doses are used and results are extrapolated to lower doses (and to human response, which is controversial)
© 2004 Brooks/Cole – Thomson LearningE
ffec
t
Dose
Nonlineardose-response
Lineardose-response
No thresholdE
ffec
tThreshold
Thresholdlevel
Dose
Figure 19-6Page 414
Usually used
LD50
0 4 8 12 16
Dose (hypothetical units)
Per
cen
tag
e o
f p
op
ula
tio
n k
illed
by
a g
iven
do
se
Figure 19-5Page 413
141062
25
50
75
100
Hormesis
Some substances that can kill us at high doses can be beneficial at low doses (digitalis)
Epidemiology
• Study of patterns of disease or toxicity to find out why some people get sick and others do not.
• Not useful for predicting affects of new technologies, substances or diseases.
• Because of uncertainty, standards for exposure to toxic chemicals or radiation are set at levels 100 to 1,000 times lower than estimated harmful levels
Ionizing radiation can cause
1) Genetic damage from mutations in DNA
2) Somatic damage: causes harm during
victims life
e.g. burns, eye cataracts, certain cancers
3) Super linear hypothesis: low doses produce more cancer per unit than high doses
4) Main source of radiation is radon
Epidemiological transition
• In 1994, 23 million people died of all causes• 39% ---> heart attacks and strokes• 24% cancer • 5% infectious diseases (pneumonia, flu, aids)• 4% accidents (2% auto)