1. Risk, Toxicology and Human Health
Chapter 17
Risk, Toxicology and Human Health

2. Risk Risk: probability of suffering harm from a hazard
- values range from: > 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?

3. © 2004 Brooks/Cole – Thomson Learning
Number of individuals affected
Very
sensitive
Majority
of population
Very
insensitive 20 40 60 80
Dose (hypothetical units)

4. 5 Types of hazards
1) cultural hazards (unsafe working conditions, criminal assault, poverty)
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 (poor diet, smoking, no exercise)

5. Nontransmissible diseases
not caused by living organism
can’t spread from person to person
e.g. diabetes

6. 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
a) virus must invade host cell and take over cell’s DNA to make more viruses

7. Transmissible diseases
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

8. 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

9. Lyme Disease
A bacterial disease spread from deer and mice to humans, tick is vector.

10. (massive epidemic = pandemic)
Viral Diseases
e.g. flu, HIV, hepatitis B, ebola, rabies
From , flu epidemic killed million people worlwide, 250,00 to 500,000 in US
(massive epidemic = pandemic)

11. 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

12. Viral Diseases West Nile virus is transmitted by mosquito bite
West Nile, SARS, and Avian flu have moved from animals to humans

13. 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

14. 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

15. 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

16. 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)

17. 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

18. 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

19. 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

20. Immune System 2 levels of defense
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

21. 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)

22. 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

23. Hormone Disrupters
1) Human-made chemicals, DDT, PCBs 2) hormone mimics ---> attack estrogen receptor molecules
3) hormone blockers ---> prevent androgen from attaching to receptor molecules
4) thyroid disrupters cause growth, brain, weight, behavior disorders

24. Hormone Disrupters 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)

25. 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

26. 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

27. 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

28. DDT in fish-eating
birds (ospreys)
25 ppm
DDT in large
fish (needle fish)
2 ppm
DDT in small
fish (minnows)
0.5 ppm
DDT in
zooplankton
0.04 ppm
DDT in water
ppm,
Or 3 ppt

29. Dose e.g. NO2, O3 react synergistically with allergens
Synergistic effects (antagonistic effects)
e.g. NO2, O3 react synergistically with allergens
LD 50 (or LC 50) dose required to kill 50% of test population
a) Poison: chemical with an LD 50 of 50 mg or
less per kg of body weight
EPA lists top 5 toxic substances:
arsenic, lead, mercury, vinyl chloride (PVC), PCBs

30. 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

31. 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.

32. 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)

33. Terms to know: Independent variable Dependent variable Control
Standard conditions
Replicates
Control group
Experimental group

34. Recommended Dose
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

35. © 2004 Brooks/Cole – Thomson Learning
Nonlinear
dose-response
Linear
dose-response
Effect
Effect
Threshold
level
Dose
Dose
No threshold
Threshold
Usually used

36. Percentage of population killed by a given dose
100 75
Percentage of population killed by a given dose 50 25
LD50 2 4 6 8 10 12 14 16
Dose (hypothetical units)

37. Some substances that can kill us at high doses
Hormesis
Some substances that can kill us at high doses
can be beneficial at low doses (digitalis)

38. 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

39. 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)