chemicals and disease… three major types of toxic agents:
TRANSCRIPT
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Chemicals and disease…
• Three major types of toxic agents:
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• Mutagens:
–Chemicals or radiation that produces mutations in DNA
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• Teratogens–Chemicals, radiation, or viruses that cause birth defects during pregnancy
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• Carcinogens–Chemicals, radiation, or viruses that cause or promote cancerous cells.
–Environmental and lifestyle factors account for up to 80% of all cancers
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• Long term exposure to various toxic chemicals in the environment can disrupt the body’s immune, nervous, and endocrine systems
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–Immune system: cells and tissues that protect the body against disease
–Nervous system: brain, spinal cord, and peripheral nerves
–Endocrine system: releases hormones into bloodstream
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•Hormone disrupters: chemicals similar to estrogens (female hormone)
•Hormone blockers: chemicals that prevent natural (male) hormones from working correctly
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–“Gender benders”
• Thyroid disrupters: affect growth and weight, may cause behavioral disorders.
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Toxicity
• A measure of how harmful a substance is
• Depends on:
– Dose: the amount of a substance ingested, inhaled, or absorbed through the skin• Frequency of exposure• Age/body size• Body detoxification• Genetic make-up
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Harm caused by a toxin depends on:
• Solubility– Water – water supply!– Oil/fat – can penetrate cell membranes
• Persistence: resistance to break-down– POP’s: Persistent Organic Pollutants
• Bioaccumulation: toxin absorbed and stored in tissues
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• Biomagnification: levels of a toxin are magnified as they pass through/up food chains
• Interactions: – Chemical– synergistic
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• Response: they type/amount of health damage– Acute: immediate
– Chronic: permanent or long lasting
Frogs and Atrazine video clip!
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Pesticides
Chapter 23
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• The IDEAL pesticide would:
–Kill ONLY the target species• (Harm NO other species)
–Breakdown easily• (No persistence)
–NOT cause genetic resistance in target species
–Be CHEAP!
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The 2 Major Categories:
• Broad Spectrum: kills target and non-target species (kills everything)
• Narrow Spectrum: (selective) kills specific group of pests
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Specific Categories
• Insecticides–Chlorinated hydrocarbons
• DDT – banned in 1972• HIGH persistance
–Organophosphates–Carbamates–Botanicals
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• Herbicides–Contact (atrazine)
–Systemic
–Soil Sterilants
–AGENT ORANGE: used in the Vietnam war – cause birth defects in animals and humans as well as cancer
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• Fungicides
• Fumigants (spays)–(Carbon tetrachloride: CCl4)
• HIGH persistance…
• Rodenticides
• Nematocides
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POP’s
• Persistent Organic Pollutants: man-made chemicals that do NOT break down–Pesticides (DDT)
–Industrial chemicals
–By-products & contaminants
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• Although some pesticides such as DDT are banned in the U.S. – companies can still manufacture and export them to other countries…–Note: the U.S. stopped
manufacturing DDT in 1985
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Problems• Genetic resistance
–Remember: insects are r-strategists so they reproduce A LOT and ADAPT/EVOLVE QUICKLY
–Remember: anti-biotic resistant bacteria… SAME THING!
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–Pesticide Treadmill: when “farmers” increase the amount of pesticide sprayed on their crops due to increased genetic resistance•Greater amounts have been shown to be ineffective…
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• Broad Spectrum pesticides kill NON-TARGET species: natural predators and parasites that HELP maintain populations of pest species
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–Wiping out natural predators can unleash new pests whose populations had previously held in check
–Pesticides are also killing honey bees which are a keystone species because of the vital job of pollination
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• Some pesticides bioaccumulate leading to disastrous problems for higher organisms (biomagnification!)
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• Human Health Affects…
–Cancers
–Nervous disorders
–Reproductive disorders
–Immune system disorders
–Birth defects
–??????
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Pesticide Benefits
• Combat insect-borne diseases (malaria)
• Increases food supplies
• Lowers food costs (?)
• Faster/Efficient
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Regulation
• Department of Health and Human Services: FDA
• USDA
• EPA
• Pesticide regulations: HAND-OUT!!
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Reductions in Pesticide Use
• IPM: Integrated Pest Management–Goal: NOT to eradicate pest
populations, but to reduce crop damage at an economically tolerable level…
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–Uses cultivation, biological, and chemical methods as part of an overall program.
–Need experts
–Initial costs are higher
–Hindered by subsidies
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“Alternative” Methods of Controlling Pests
• Cultivation Practices:–Crop rotation
–Intercropping, polyculture, polyvarietal practices
–Adjust planting times
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• Biological pest control:–Provide habitats for pests’
natural enemies (spiders’ huts in China)• Spiders kill more insects than insecticides do!!!
–Import natural predators (also bacteria, viruses, parasites)
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• Insect birth control•Sterilize the males
• Lure pests away using pheromones
• Disrupt life cycles using hormones
• Hot water
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• Organic methods:–Soap spray–Tobacco spray–Alcohol spray–Bt (Bacillus thurengienses)–Neem–Pyrethrins (from chrysanthemum)–Cayenne pepper–Citrus oil
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• Create GMO’s (Bt Corn)
• Irradiation