Transcript Chapter 9: Environmental Health & Toxicology

Chapter 9: Environmental Health & Toxicology
In this chapter we will cover the following topics:
I. Types of Environmental Health Hazards
II. Movement, Distribution, and Fate of Toxins
III. Mechanisms for Minimizing Toxic Effects
IV. Measuring Toxicity
V. Risk Assessment and Acceptance
VI. Establishing Public Policy
Types of Environmental Health Hazards
The World Health Organization
Under U.N. agreement, the World Health Organization (WHO) was
founded in 1946, with roots that extend back into cholera
epidemics of the 1830's. The WHO publishes an annual report on global
health status. .
Infectious Organisms
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Infectious disease is 43% of all disease deaths annually
Adults: infections of respiratory tract represent highest mortality
Children: diarrhea represents highest mortality
AIDS: 30 million people infected worldwide, too expensive
($10,000/year) to treat in poor countries
Eradication: smallpox 1977, polio by year 2000
Immunizations: in transgenic crops which would reach more people
Table 9.1 -- Leading Causes of Death Worldwide
Disease
Cardiovascular disease
Cancers
Chronic lung disease
Acute lung diseases
Injuries
Perinatal conditions
Diarrhea
HIV/AIDS
Malaria
Vaccine-preventable infections
Other known diseases
Unknown
Total
Source: World Health Organization, 1997
Millions of deaths / year
9.7
6.0
5.5
4.1
4.0
3.2
3.0
2.3
2.0
1.7
3.6
5.9
51.0
Morbidity and Quality of Life
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DALY - disability-adjusted life year: attempt to measure other health
factors besides death
90% of losses measured by DALY occur in developing countries
preventable measures: malnutrition, sanitation, clean water,
childhood inoculations could reduce infections
parasitic diseases contribute to poor health; combated by donations
of drugs e.g., ivermectin for riverblindness
Table 9.2 -- Annual Disease Burden in Poor Households
Disease Group
Main Source DALY Burden* Feasible Reduction
(millions/year)
(%)
---------------------------------------------------------------------------------------Respiratory infections Indoor Air pollution,
crowding
119
15
Diarrhea
Water supply, sanitation
99
40
Tuberculosis
Crowding, malnutrition
46
10
Chronic respiratory
diseases & cancer
Indoor air pollution,
crowding
45
10
Parasites, worms
Garbage disposal,
sanitation
26
30
Trachoma
Water supply, hygiene
8
10
---------------------------------------------------------------------------------------------------------*Disability Adjusted Life Years = years lost from premature death and disability
Source: World Bank, World Development Report 1998
Emergent diseases and environmental change
• Emergent Disease: disease never known before or one that has
been absent for at least 20 years.
- e.g., Ebola
• High population density combined with loss of ecosystem
components that normally control disease vectors, allows for
appearance and spread of contagious diseases.
- e.g., Hanta virus in U.S. - ecological change supports high
deer mouse (vector) populations
• High travel rates help spread disease organisms all over the
globe, especially dormant species that can breakout when moved to
new location
Antibiotic and pesticide resistance
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Malaria - mostly Africa, both vector and disease protozoan are
resistant to control measures
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Natural selection: repeated low-level exposures selectively produce
resistant organisms
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Resistant strains: Tuberculosis, Staphylococcus A
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Reasons: indiscriminant use of antibiotics and pesticides
Toxic Chemicals
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Hazardous: dangerous
- flammables, explosives, irritants, sensitizers, acids, and
caustics
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Toxins: poisonous
- react with specific cellular components to kill cells
- Allergens and antigens: activate immune response
- Immune depressants, unclear how these act on bodily
function
- Neurotoxins, fast acting
- Mutagens, alter DNA
- Teratogens: embryo disruptions, thalidomide, alcohol
- Carcinogens: mortality decreasing over last 30 years
Table 9.3 -- Toxic Chemicals in the United States Causing the
Greatest Risk to Human Health
---------------------------------------------------------------------------------------Benzene
Mercury
Cadmium
Methyl ethyl ketone
Carbon tetrachloride
Methyl isobutyl ketone
Chloroform
Nickel
Chromium
Tetrachloroethylene
Cyanides
Toluene
Dichloromethane
Trichloroethane
Lead
Trichloroethylene
Xylene(s)
---------------------------------------------------------------------------------------Source: Data from Environmental Protection Agency.
Natural and Synthetic Toxins
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Concept of chemical warfare among plants and animals leads to
powerful natural toxins
Many more natural pesticides in diet than synthetic
Must not underestimate the actual danger of both synthetic and
natural toxins
Physical Agents, Trauma, and Stress
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Radiation, noise, other electromagnetic energy
Trauma: a principle cause of death e.g., car accidents
Stress: physical, chemical, or emotional
Diet
High fat, salt diet associated with disease; low protein, high fiber diet
associated with longevity
Movement, Distribution, and Fate of Toxins
Routes of toxin introduction determines effects
Solubility
Is a chemical oil or water soluble?
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Oil soluble chemical more likely to enter a cell and stay in body
Bioaccumulation and Biomagnification
1.Bioaccumulation: selective absorption
2.Biomagnification: movement of toxin from prey into predator
Persistence
Plastics, pesticides (DDT) are used because they "stay around" but
also better chance of interaction with unintended organism
Chemical Interactions
Antagonistic, additive, synergistic
Table 9.5 Factors in Environmental Toxicity
Factors Related to the Toxic Agent
1.Chemical composition and reactivity
2.Physical characteristics (such as solubility, state)
3.Presence of impurities or contaminants
4.Stability and storage characteristics of toxic agent
5.Availability of vehicle (such as solvent) to carry agent
6.Movement of agent through environment and into cells
Factors Related to Exposure
1.Dose (concentration and volume of exposure)
2.Route, rate, and site of exposure
3.Duration and frequency of exposure
4.Time of exposure (time of day, season, year)
Factors Related to Organism
1.Resistance to uptake, storage, or cell permeability of agent
2.Ability to metabolize, inactivate, sequester, or eliminate agent
3.Tendency to activate or alter nontoxic substances so they become toxic
4.Concurrent infections or physical or chemical stress
5.Species and genetic characteristics of organism
6.Nutritional status of subject
7.Age, sex, body weight, immunological status, and maturity
Mechanisms for Minimizing Toxic Effects
Every substance is toxic at some dose--
"What is there that is not poison? All things are poison and
nothing [is] without poison. Solely the dose determines
that a thing is not a poison."
-- Paracelsus (1493-1541)
Metabolic Degradation and Excretion
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Liver: enzyme systems detoxify and help excretion out of body,
can also convert substances into carcinogens
Excretion: bladder and kidney can be exposed to the toxins
intended for removal
Repair Mechanisms
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DNA, protein, cells all have repair mechanisms to replace worn or
damaged parts
Tissues with high level of cell growth and replacement can be a
site of unregulated growth if under stress (cancer)
Measuring Toxicity
Dose and route of exposure
Animal Testing
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Time consuming, expensive
Not all animals are sensitive to same dose, not all human
individuals have same sensitivity
Description: LD50
Toxicity Ratings
Many carcinogens may be toxic at doses below direct toxicity
measuring techniques
Table 9.6 -- Acute lethal does for some toxic organic chemicals.
Chemical
Exposure
LD50
----------------------------------------------------------------------------------Ricin (castor bean)
Ivn-mus
Orl-rat
3ng/kg
100 mg/kg
Botulism toxin
Ipr-mus
160 ng/kg
Dioxin (tetrachlorodioxin)
Orl-gpg
Orl-hmstr
600 ng/kg
3 mg/kg
Muscarine (mushroom poison)
Ivn-mus
250 ug/kg
Parathion (insecticide)
Ipr-rat
1.5 mg/kg
Aflatoxin (fungal toxin)
rl-mky
1.75 mg/kg
Nicotine
Ivn-cat
Orl-rat
Orl-hum
Orl-rat
Orl-hum
2 mg/kg
53 mg/kg
50 mg/kg
60 mg/kg
80 mg/kg
DDT
Toxaphene
2,4-D
Source: Data from Registry of Toxic Effects of Chemical Substances,
National Institute for Occupational Safety and Health, 1985
Orl= oral, ivn = intravenous, ipr = intraperitoneal, mus = mouse; mky = monkey, hmstr = hamster, hum = human, gpg = guinea pig
Nanogram (ng) = 1 X10-9 g; Microgram (ug) = 1 X 10-6 g; Milligram (mg) = 1 X 10-3 g
Acute versus Chronic Doses and Effects
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Acute = single dose causes some health effect
Chronic = long term effects from single or repeated exposure
Delaney Clause 1958, No Reasonable Harm 1996
Detection Limits
Technology allow detection of chemicals at levels that may or may not
indicate more prevalence than in past
Risk Assessment and Acceptance
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Risk = probability of harm X probability of exposure
Assessing Risks
Relative risk and perceptions
1. De-emphasize risk of activities we enjoy
2. Understanding "chance in 100" type assessments
3. Personal experience plays a role in perceived risk
4. Ability to control our own fate is over estimated
5. News media accounts of risk are not always "real"
6. Familiarity (or lack thereof) affects perception of risk
Accepting Risks
Reaction to emotion is more persuasive than statistics: more people
willing to accept an activity (automobile driving) that is much more
dangerous than nuclear energy and other high emotion, but
low risk encounters
Establishing Public Policy
• Scientific results may not provide enough information for
establishing public health risks (saccharin, aspartame)
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Standard setting needs to consider:
1.Combined effects from different sources
2.Sensitivities
3.Chronic and acute exposures
• Difficult to find line between repair mechanisms maintaining healthy
status and risk of bodily damage
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Policy decisions need to consider ecological impacts (EPA)
Table 9.7 -- Activities Estimated to Increase Your Chances of Dying in any Given Year by 1
in 1 Million
Activity
Resulting Death Risk
---------------------------------------------------------------------------------------------Smoking 1.4 cigarettes
Cancer, heart disease
Dinking 0.5 liter of wine
Cirrhosis of the liver
Spending 1 hour in a coal mine
Black lung disease
Living 2 days in New York or Boston
Air pollution
Traveling 6 minutes by canoe
Accident
Traveling 10 miles by bicycle
Accident
Traveling 150 miles by car
Accident
Flying 1000 miles by jet
Accident
Flying 6000 miles by jet
Cancer caused by cosmic radiation
Living 2 months in Denver
Cancer caused by cosmic radiation
Living 2 months in a stone or brick building Cancer caused by natural radioactivity
One chest X ray
Cancer caused by radiation
Living 2 months with a cigarette smoker
Cancer, heart disease
Eating 40 tablespoons of peanut butter
Cancer from aflatoxin
Living 5 years at the site boundary of a
Cancer caused by radiation from routine leaks
typical nuclear power plant
Living 50 years 5 miles from a nuclear
Cancer caused by accidental radiation release
power plant
Eating 100 charcoal-broiled steaks
Cancer from benzopyrene
-----------------------------------------------------------------------------------------------From William Allman, "Staying Alive in the Twentieth Century," Science 85, 5(6): 31 October 1985.
Used by permission of the author
Table 9.8 -- Relative Risks to human welfare
Relatively High-Risk Problems
• Habitat alteration and destruction
• Species extinction and loss of biological diversity
• Stratospheric ozone depletion
• Global climate change
Relatively Medium-Risk Problems
• Herbicides/pesticides
• Toxics and pollutants in surface waters
• Acid deposition
• Airborne toxics
Relatively Low-Risk Problems
• Oil spills
• Groundwater pollution
• Radionuclides
• Thermal pollution
Source: Data from Environmental Protection Agency
Summary
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Health a state of physical, mental, social well-being, not just absence
of disease
Most important health threats: pathogenic organisms (especially
emergent and resistant microorganisms)
Stress, diet, and lifestyle: important health factors
Dose of toxic exposure can be difficult to equate with health risk
Distribution of materials in environment depend on may factors:
physical, chemical, transport in and out of organisms
Forced to use estimators of actual risk; leads to many questions
regarding health