chemicals and disease… three major types of toxic agents:

Chemicals and disease…

• Three major types of toxic agents:

• Mutagens:

–Chemicals or radiation that produces mutations in DNA

• Teratogens–Chemicals, radiation, or viruses that cause birth defects during pregnancy

• Carcinogens–Chemicals, radiation, or viruses that cause or promote cancerous cells.

–Environmental and lifestyle factors account for up to 80% of all cancers

• Long term exposure to various toxic chemicals in the environment can disrupt the body’s immune, nervous, and endocrine systems

–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

•Hormone disrupters: chemicals similar to estrogens (female hormone)

•Hormone blockers: chemicals that prevent natural (male) hormones from working correctly

–“Gender benders”

• Thyroid disrupters: affect growth and weight, may cause behavioral disorders.

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

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

• Biomagnification: levels of a toxin are magnified as they pass through/up food chains

• Interactions: – Chemical– synergistic

• Response: they type/amount of health damage– Acute: immediate

– Chronic: permanent or long lasting

Frogs and Atrazine video clip!

Pesticides

Chapter 23

• 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!

The 2 Major Categories:

• Broad Spectrum: kills target and non-target species (kills everything)

• Narrow Spectrum: (selective) kills specific group of pests

Specific Categories

• Insecticides–Chlorinated hydrocarbons

• DDT – banned in 1972• HIGH persistance

–Organophosphates–Carbamates–Botanicals

• Herbicides–Contact (atrazine)

–Systemic

–Soil Sterilants

–AGENT ORANGE: used in the Vietnam war – cause birth defects in animals and humans as well as cancer

• Fungicides

• Fumigants (spays)–(Carbon tetrachloride: CCl4)

• HIGH persistance…

• Rodenticides

• Nematocides

POP’s

• Persistent Organic Pollutants: man-made chemicals that do NOT break down–Pesticides (DDT)

–Industrial chemicals

–By-products & contaminants

• 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

Problems• Genetic resistance

–Remember: insects are r-strategists so they reproduce A LOT and ADAPT/EVOLVE QUICKLY

–Remember: anti-biotic resistant bacteria… SAME THING!

–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…

• Broad Spectrum pesticides kill NON-TARGET species: natural predators and parasites that HELP maintain populations of pest species

–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

• Some pesticides bioaccumulate leading to disastrous problems for higher organisms (biomagnification!)

• Human Health Affects…

–Cancers

–Nervous disorders

–Reproductive disorders

–Immune system disorders

–Birth defects

–??????

Pesticide Benefits

• Combat insect-borne diseases (malaria)

• Increases food supplies

• Lowers food costs (?)

• Faster/Efficient

Regulation

• Department of Health and Human Services: FDA

• USDA

• EPA

• Pesticide regulations: HAND-OUT!!

Reductions in Pesticide Use

• IPM: Integrated Pest Management–Goal: NOT to eradicate pest

populations, but to reduce crop damage at an economically tolerable level…

–Uses cultivation, biological, and chemical methods as part of an overall program.

–Need experts

–Initial costs are higher

–Hindered by subsidies

“Alternative” Methods of Controlling Pests

• Cultivation Practices:–Crop rotation

–Intercropping, polyculture, polyvarietal practices

–Adjust planting times

• 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)

• Insect birth control•Sterilize the males

• Lure pests away using pheromones

• Disrupt life cycles using hormones

• Hot water

• Organic methods:–Soap spray–Tobacco spray–Alcohol spray–Bt (Bacillus thurengienses)–Neem–Pyrethrins (from chrysanthemum)–Cayenne pepper–Citrus oil

• Create GMO’s (Bt Corn)

• Irradiation