Pest Management and
Toxicology
How Can We Protect Crops from Pests More
Sustainably?
• We can sharply cut pesticide use without decreasing crop yields by using
a mix of cultivation techniques, biological pest controls, and small
amounts of selected chemical pesticides as a last resort (integrated pest
management).
Nature Controls the Populations of
Most Pests
• What is a pest?
• Interferes with human welfare
• Natural enemies—predators, parasites, disease organisms—control
pests
• In natural ecosystems
• In many polyculture agroecosystems
• What will happen if we kill the pests?
Natural Capital: Spiders are Important
Insect Predators
Fig. 12-21, p. 297
We Use Pesticides to Try to Control
Pest Populations
• Pesticides
•
•
•
•
Insecticides
Herbicides
Fungicides
Rodenticides
Natural pesticides
• Herbivores overcome plant defenses through natural selection:
coevolution
We Use Pesticides to Try to Control
Pest Populations
• First-generation pesticides
• Borrowed from plants
• Second-generation pesticides
• Lab produced: DDT and others
• Benefits versus harm
• Broad-spectrum and narrow-spectrum agents
• Persistence varies
Individuals Matter: Rachel Carson
• Biologist
• Silent Spring
• Potential threats of uncontrolled use of pesticides
Rachel Carson, Biologist
Fig. 12-B, p. 298
Modern Synthetic Pesticides Have Several
Advantages
• Save human lives
• Increases food supplies and profits for farmers
• Work quickly
• For many, health risks are very low relative to benefits
• New pest control methods: safer and more effective
Modern Synthetic Pesticides Have Several
Disadvantages
• Accelerate rate of genetic resistance in pests
• Expensive for farmers
• Some insecticides kill natural predators and parasites
that help control the pest population
• Pollution in the environment
• Some harm wildlife
• Some are human health hazards
Pesticide Use Has Not Reduced U.S. Crop Losses to
Pests
• David Pimentel: Pesticide use has not reduced U.S. crop loss to pests
• 1942-1997: crop losses from insects increased from 7% to 13%, even with
10x increase in pesticide use
• High environmental, health, and social costs with use
• Use alternative pest management practices
• Pesticide industry disputes these findings
Trade-Offs: Conventional Chemical
Pesticides
Fig. 12-22, p. 299
What Can You Do? Reducing Exposure to
Pesticides
Fig. 12-23, p. 300
Case Study: Ecological Surprises: The Law
of Unintended Consequences
• 1955: Dieldrin (DDT relative) sprayed to control mosquitoes
• Malaria was controlled
• Dieldrin didn’t leave the food chain
• Domino effect of the spraying
• Happy ending
Laws and Treaties Can Help to Protect Us from
the Harmful Effects of Pesticides
• U.S. federal agencies and laws
• EPA, USDA, FDA
• Fungicide and Rodenticide Act, 1947 – assess health risk of active ingredients in
pesticide products.
• Food Quality Protection Act, 1996 – reduce pesticide residue on food by factor of 10
• Effects of active and inactive pesticide ingredients are poorly documented
• U.S. exports many banned pesticides
• Circle of poison
There Are Alternatives to Using Pesticides
• Fool the pest
• Crop rotation; changing planting times
• Provide homes for pest enemies
• Polyculture
• Implant genetic resistance – genetic engineering
• Bring in natural enemies
• Predators, parasites, diseases
There Are Alternatives to Using Pesticides
• Use insect perfumes
• pheromones
• Bring in hormones
• Interfere with pest life cycle
• Alternative methods of weed control
• Crop rotation, cover crops, mulches
Solutions: An Example of Genetic
Engineering to Reduce Pest Damage
Fig. 12-24, p. 302
Natural Capital: Biological Pest Control
Fig. 12-25, p. 302
Integrated Pest Management Is a
Component of Sustainable Agriculture
• Integrated pest management (IPM)
• Coordinate: cultivation, biological controls, and chemical tools to reduce
crop damage to an economically tolerable level
• Reduces pollution and pesticide costs
• Disadvantages
• Requires expert knowledge
• High initial costs
• Government opposition
Core Case Study: Are Baby Bottles and Food Cans Safe To Use? The
BPA Controversy
• Some synthetic chemicals act as hormone mimics and disrupt the
human endocrine system
• Excess estrogen effects on males
•
•
•
•
Feminization
Smaller penis
Lower sperm counts
Presence of both male and female sex organs
Core Case Study: Are Baby Bottles and Food Cans Safe To Use? The
BPA Controversy
• BPA (bisphenol A)
• Estrogen mimic
• In polycarbonates and other hardened plastics
• Baby bottles and sipping cups
• Reusable water bottles
• Sports drink and juice bottles
• Microwave dishes
• Food storage containers
• Liners of most food and soft drink cans
Core Case Study: Are Baby Bottles and Food Cans Safe To Use? The
BPA Controversy
• BPA leaches into foods and drinks
• Even when containers not heated
• 93% of Americans older than 6 have BPA levels above the threshold
level set by the EPA
• Higher in children and adolescents
• Risks for infants, children, adults
Baby Drinking from BPA Bottle
Fig. 17-1, p. 436
What Major Health Hazards
Do We Face?
• We face health hazards from biological, chemical, physical, and cultural
factors, and from the lifestyle choices they make.
Risks Are Usually Expressed as Probabilities
• Risk
• Probability of suffering harm from a hazard
• Probability vs. possibility
• Risk Assessment
• Risk Management
Science: Risk Assessment and Risk Management
Fig. 17-2, p. 437
We Face Many Types of Hazards
1. Biological:
•
Pathogen: an organism that causes disease in other organisms
2. Chemical
3. Physical
4. Cultural
5. Lifestyle choices
What Types of Biological Hazards Do
We Face?
• The most serious biological hazards we fade are infectious diseases such
as flu, AIDS, tuberculosis, diarrheal diseases, and malaria.
Some Diseases Can Spread from One Person to Another
• Infectious disease
• Pathogen invades the body and multiplies
• Transmissible disease
• Contagious or communicable disease
• Infectious disease transmitted between people
• Flu, tuberculosis, measles
Some Diseases Can Spread from One Person to Another
• Nontransmissible disease
• Not caused by living organisms
• Heart disease, most cancers, diabetes
• Since 1950, death from infectious diseases have declined due to
•
•
•
•
Better health care
Better sanitation
Antibiotics
Vaccines
Infectious Diseases Are Still Major
Health Threats
• Infectious diseases spread through
•
•
•
•
Air
Water
Food
Body fluids
• Epidemics and pandemics
• Resistance of bacteria and insects to drugs and pesticides
Science: Pathways for Infectious Diseases in Humans
Fig. 17-3, p. 439
Major Causes of Death from Infectious Diseases
in the World, 2007
Fig. 17-4, p. 439
Science Focus: Genetic Resistance to Antibiotics Is
Increasing
• Bacteria: rapid reproduction, easily spread
• Overuse of antibiotics
• Overuse of pesticides
Science Focus: Genetic Resistance to Antibiotics Is
Increasing
• Methicillin-resistant Staphylococcus aureus (MRSA)
• Resistant to most antibiotics
• Symptoms of MRSA
• How will it be controlled?
Case Study: The Growing Global Threat from Tuberculosis
• One in ten will become sick with TB
• 1.8 million deaths each year, primarily in less-developed countries
• Why is tuberculosis on the rise?
•
•
•
•
Not enough screening and control programs
Genetic resistance to a majority of effective antibiotics
Person-to-person contact has increased
AIDS individuals are very susceptible to TB
Lung Tissue Destroyed by Tuberculosis
Fig. 17-5, p. 440
Individuals Matter: Three College Students Have Saved
Thousands of Lives
• North Carolina State seniors
• Developed a device that can detect TB bacteria on a slide
• Very useful in less-developed countries
Viral Diseases and Parasites Kill Large
Numbers of People
• Influenza or flu virus
• #1 Killer
• HIV
• #2 Killer
• Hepatitis B virus (HBV)
• #3 Killer
• Emergent diseases: West Nile virus
Viral Diseases and Parasites Kill Large
Numbers of People
• Viruses that move form animals to humans
• West Nile virus
• Ecological medicine
• Reduce chances of infection:
1. Wash your hands
2. Avoid touching your face
3. Avoid sick people
Science Focus: Ecological Medicine: How Humans Get Infectious
Diseases from Animals
• Ecological medicine
• Human practices that encourage the spread of diseases from animals to
humans
• Emerging infections
•
•
•
•
HIV
Avian flu
Hepatitis B
Lyme virus
Case Study: Global HIV/AIDS Epidemic
• Acquired immune deficiency syndrome (AIDS)
• caused by human immunodeficiency virus (HIV)
• Many secondary infections
• No vaccine to prevent or cure AIDS
• Expensive drugs—live longer
Case Study: Global HIV/AIDS Epidemic
• 25 million deaths, so far
• #1 killer globally of women 15-49
• Most prevalent in sub-Saharan Africa
• Life expectancy dropped from 62 to 47
• Alters age structure of population
Case Study: Malaria — The Spread of a Deadly Parasite
• Malaria
•
•
•
•
•
Caused by Plasmodium sp. carried by Anopheles mosquitoes
Tropical and subtropical regions
Spread
Symptoms
Malarial cycle
Case Study: Malaria — The Spread of a Deadly Parasite
• Malaria on the rise since 1970
•
•
•
•
Drug resistant Plasmodium
Insecticide resistant mosquitoes
Clearing of tropical forests
AIDS patients particularly vulnerable
• Prevention of spread and current research
Global Outlook: Distribution of Malaria
Fig. 17-6, p. 444
A Boy in Brazil’s Amazon Sleeps Under an
Insecticide-Treated Mosquito Net
Fig. 17-7, p. 445
We Can Reduce the Incidence of Infectious Diseases
• Good news
• Vaccinations on the rise
• Oral rehydration therapy
• Bad news
• More money needed for medical research in developing countries
Solutions: Infectious Diseases
Fig. 17-8, p. 445
What Types of Chemical Hazards
Do We Face?
• There is growing concern about chemicals in the environment that can
cause cancers and birth defects, and disrupt the human immune,
nervous, and endocrine system.
Some Chemicals Can Cause Cancers, Mutations, and Birth
Defects
• Toxic chemicals
• Carcinogens
• Chemicals, types of radiation, or certain viruses the cause or promote cancer
• Mutagens
• Chemicals or radiation that cause mutations or increase their frequency
• Teratogens
• Chemicals that cause harm or birth defects to a fetus or embryo
Case Study: PCBs Are Everywhere—A Legacy from the
Past
• Class of chlorine-containing compounds
•
•
•
•
•
•
•
Very stable
Nonflammable
Break down slowly in the environment
Travel long distances in the air
Fat soluble
Biomagnification
Food chains and webs
• Banned, but found everywhere
Potential Pathways on Which Toxic Chemicals Move Through
the Environment
Fig. 17-9, p. 447
Some Chemicals May Affect Our Immune and Nervous
Systems
• Some natural and synthetic chemicals in the environment can weaken
and harm
• Immune system
• Nervous system
• Neurotoxins: PCBs, arsenic, lead, some pesticides
• Endocrine system
Science Focus: Mercury’s Toxic
Effects
• Hg: teratogen and potent neurotoxin
•
•
•
•
Once airborne, persistent and not degradable
1/3 from natural sources
2/3 from human activities
Enters the food chain: biomagnification
• How are humans exposed?
1. Inhalation: vaporized Hg or particulates
2. Eating fish with high levels of methylmercury
3. Eating high-fructose corn syrup
Science Focus: Mercury’s Toxic
Effects
• Effects of Hg on humans
• Damage nervous system, kidneys, lungs
• Harm fetuses and cause birth defects
• Who is most at risk?
• Pregnant women
• 75% of exposure comes from eating fish
Solutions: Mercury Pollution
Fig. 17-10, p. 449
Some Chemicals Affect the Human Endocrine System
• Glands that release hormones that regulate bodily systems and control
sexual reproduction, growth, development, learning, behavior
• Hormonally active agents have similar shapes and bind to hormone
receptors
•
•
•
•
Gender benders
Thyroid disruptors
BPA?
Phthalates in plastics
Hormones and Hormones Mimics or Blockers
Fig. 17-11, p. 449
How Can We Evaluate and Deal with Chemical Hazards?
• Scientists use live laboratory animals, case reports of poisonings, and
epidemiological studies to estimate the toxicity of chemicals, but these
methods have limitations.
• Many health scientists call for much greater emphasis on pollution
prevention to reduce our exposure to potentially harmful chemicals.
Many Factors Determine the Harmful Health Effects of a
Chemical
• Toxicology
• Toxicity dependent on
•
•
•
•
•
•
•
Dose
Age
Genetic makeup
Multiple chemical sensitivity (MCS)
Solubility
Persistence
Biomagnification
Many Factors Determine the Harmful Health Effects of a
Chemical
• Response
• Acute effect: immediate or rapid
• Chronic effect: permanent or long-lasting
Science: Estimating Human Exposure to
Chemicals and Measuring Their Effects
Fig. 17-12, p. 452
Case Study: Protecting Children from Toxic Chemicals
• Analysis of umbilical cord blood: significance
• Infants and children more susceptible
• Eat, drink water, and breathe more per unit of body weight than adults
• Put their fingers in their mouths
• Less well-developed immune systems and body detoxification processes
• Fetal exposure may increase risk of autism, asthma, learning disorders
Scientists Use Live Lab Animals and Nonanimal Tests to Estimate
Toxicity
• Mice and rats
• Systems are similar to humans
• Small, and reproduce rapidly
• Is extrapolation to humans valid?
• Dose-response curve: median lethal dose (LD50)
• Nonthreshold dose-response model
• Threshold dose-response model
Scientists Use Live Lab Animals and Nonanimal Tests to Estimate
Toxicity
• More humane methods using animals
• Replace animals with other models
• Computer simulations
• Tissue culture and individual animal cells
• Chicken egg membranes
• What are the effects of mixtures of potentially toxic chemicals?
Hypothetical Dose-Response Curve Showing Determination of
the LD50
Fig. 17-13, p. 453
Toxicity Ratings and Average Lethal Doses for Humans
Table 17-1, p. 453
Science: Two Types of Dose-Response Curves
Fig. 17-14, p. 454
There Are Other Ways to Estimate the Harmful Effects of
Chemicals
• Case reports and epidemiological studies
• Limitations of epidemiological studies
•
•
•
•
Too few people tested
Length of time
Can you link the result with the chemical?
Cannot be used for new hazards
Are Trace Levels of Toxic Chemicals Harmful?
• Insufficient data for most chemicals
• We are all exposed to toxic chemicals
• Are the dangers increasing or are the tests just more sensitive?
Some Potentially Harmful Chemicals Found in
Most Homes
Fig. 17-15, p. 455
Why Do We Know So Little about the Harmful Effects of
Chemicals?
• Severe limitations estimating toxicity levels and risks
• Only 2% of 100,000 chemicals have been adequately tested
• 99.5% of chemicals used in the United States are not supervised by
government
Pollution Prevention and the Precautionary Principle
• Those introducing a new chemical or new technology would have to follow new
strategies
• A new product is considered harmful until it can be proved to be safe
• Existing chemicals and technologies that appear to cause significant harm must be
removed
• 2000: global treaty to ban or phase out the dirty dozen persistent organic pollutants
(POPs)
• 2007 REACH program in the European Union
Individuals Matter: Ray Turner and
His Refrigerator
• 1974: Ozone layer being depleted by chlorofluorocarbons (CFCs)
• 1992: International agreement to phase out CFCs and other ozonedestroying chemicals
• Ray Turner: citrus-based solvents to clean circuit boards
How Do We Perceive Risks and How Can We Avoid the Worst of
Them?
• We can reduce the major risks we face by becoming informed, thinking
critically about risks, and making careful choices.
The Greatest Health Risks Come from Poverty, Gender,
and Lifestyle Choices
• Risk analysis
• Risk assessment
• Risk management
• Risk communication
• Greatest health risks
• Poverty
• Gender
• Lifestyle choices
Global Outlook: Number of Deaths per Year in the World
from Various Causes
Fig. 17-16, p. 458
Comparison of Risks People Face in Terms of
Shorter Average Life Span
Fig. 17-17, p. 459
Case Study: Death from Smoking
• Most preventable major cause of suffering and premature death
• Premature death of 5.4 million per year globally and 442,000 in the United
States
• Could be linked to increased dementia and Alzheimer’s disease
• Nicotine: additive
• Effects of passive smoking (secondhand smoke)
Case Study: Death from Smoking
• How to reduce smoking
•
•
•
•
Taxes
Classify and regulate nicotine
Bans on smoking in public places
Education
Normal Lung and Emphysema Lung
Fig. 17-18, p. 459
Annual Deaths in the U.S. from Tobacco Use and Other
Causes
Fig. 17-19, p. 460
Estimating Risks from Technologies
Is Not Easy
• System reliability (%) = Technological reliability (%) x Human reliability
(%)
• To err is human…
Most People Do a Poor Job of Evaluating Risks
1. Fear
2. Degree of control
3. Whether a risk is catastrophic or chronic
4. Optimism bias
5. Want instant gratification without thinking of future harm
Several Principles Can Help Us to Evaluate and Reduce
Risk
1. Compare risks
2. Determine how much you are willing to accept
3. Determine the actual risk involved
4. Concentrate on evaluating and carefully making important lifestyle
choices
Three Big Ideas
1. We face significant hazards from infectious diseases, malaria, and
tuberculosis, and from exposure to chemicals that can cause cancers
and birth defects, and disrupt the human immune, nervous, and
endocrine systems.
2. Because of the difficulty in evaluating the harm caused by exposure to
chemicals, many health scientists call for much greater emphasis on
pollution prevention.
Three Big Ideas
3. Becoming informed, thinking critically about risks, and making careful
choices can reduce the major risks we face.