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Pesticides Ch 22.  PEST = any organism that interferes in some way with human welfare or activities.  PESTICIDE = toxic chemicals used to reduce the.

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Presentation on theme: "Pesticides Ch 22.  PEST = any organism that interferes in some way with human welfare or activities.  PESTICIDE = toxic chemicals used to reduce the."— Presentation transcript:

1 Pesticides Ch 22

2  PEST = any organism that interferes in some way with human welfare or activities.  PESTICIDE = toxic chemicals used to reduce the size of and control the pest population.  Grouped by their target organism Insecticide, Herbicide, Fungicide, Rodenticide  85% of pesticides worldwide used for Agriculture.

3  “Ideal Pesticides”  Narrow-Spectrum = kill only target organism.  Breaks down easily into safe materials  Does not move around in the environment.  “Non-Ideal Pesticides”  Broad-Spectrum = kill more than just the target.  Persistent or Can degrade into other cmpds that can be more dangerous  Move around in the environment.

4  Pre-1940s (First-generation pesticides)  Inorganics (Minerals)  Contain lead, mercury, and arsenic  Very persistent & bioaccumulate  Organics (Botanicals)  Plant-derived  Break down readily  Post-1940s (Second-generation pesticides)  Synthetic Botanicals  Made by altering natural botanicals  Ex: dichlorodiphenyltrichloroethane (DDT)

5 INSECTICIDES : Classified by chemical structure  Chlorinated Hydrocarbons = organic cmpd + Cl  Broad-spectrum, persistent  Most are banned (DDT, endosulfan, etc)  Rachel Carson: Silent Spring  Organophosphates = organic cmpd + P  more poisonous than most others  not persistent, so they’ve replaced most chlorinated hydrocarbons  Carbamates = broad-spectrum, derived from carbamic acid  Less toxic to mammals (Carbaryl, Aldicarb)

6 HERBICIDES  Classified by how they act & what they kill  Selective Herbicides = kill only certain types of plants  Broad-leaf Herbicides  2,4-D & 2,4,5-T common in 1940s  2,4,5-T banned by EPA in 1979 due to possible harmful side effects realized after its use in the Vietnam War  Grass Herbicides  Nonselective Herbicides = kill all vegetation

7 VIETNAM WAR & HERBICIDES  US used mixtures of herbicides to kill vegetation in S.Vietnam to expose hiding places & destroy crops planted by Vietcong: Agent White, Agent Blue, & Agent Orange  Negative environmental impacts:  Mangrove forests & hardwood forests destroyed  Harmed ecology & economy of S.Vietnam  Negative health impacts:  Agent Orange = 2,4-D & 2,4,5-T combined.  Created highly toxic Dioxins during creation  Birth defects, stillbirths, female reproductive disorders, soft-tissue cancers  Bioaccumulated in fish = very high levels in Vietnamese people

8  DISEASE CONTROL  Malaria: carried mostly by female mosquitoes  Worldwide: 300-500M people currently suffer, 2.7M die each year.  DDT has helped the malaria problem greatly.  Sri Lanka: went from 2M cases each year to almost zero with the use of DDT.  When spraying stopped, more than 1M cases per year within 4 years.  Restarted DDT spraying in 1968  DDT still used in at least 20 tropical countries to control mosquitoes.

9 CROP PROTECTION- We already know this…  1/3 of world’s crops are eaten/destroyed by pests  Pesticides decrease crop loss due to weed competition, insect consumption, and plant diseases caused by pathogens = microorganisms that cause disease.  Many insects are considered pests, and ~200 species have the potential to cause large economic losses in agriculture.  Pesticide use is justified economically:  For every $1 spent by farmers on pesticides, $3-5 is saved from crop loss.  Monoculture = one variety of crop species is grown on large tracts of land.  Causes more pest destruction because it reduces the dangers and accidents that might befall a pest as it searches for food.

10 Genetic Resistance  any inherited characteristic that decreases the effect of a pesticide on a pest.  520 insect & mite species & 84 weed species currently resistant  Evolution causes genetic resistance (any cumulative genetic change in a population of organisms).  Natural genetic traits protect some individuals from the pesticide, and their traits move onto the next generation.  Short generation times & large population sizes promote rapid evolution & quick adaptation.

11  Pesticide Treadmill = the cost of applying pesticides increases while their effectiveness decreases (due to genetic resistance)  Resistance Management = delay the evolution of genetic resistance to maximize the time a pesticide remains effective.  Maintain a nearby “refuge” of untreated plants. Pests there won’t be affected, and will breed with the newly resistant pests to keep the gene pool variable.  Avoid repeated use of same herbicide on the same field.

12 Ecosystem Imbalances  Pesticides affect species other than intended pests.  Beneficial insects, birds, and others are often killed.  Indirectly responsible for killing many natural enemies of the pests (may starve/migrate looking for food after pesticide use)  Kill natural enemies directly sometimes  eating prey who have pesticides in their bodies  Pest population rebounds soon due to lack of predators!  Creation of new pests (minor pests become major pests)  Pesticide may kill a certain pest’s natural predators, parasites, and competitors.

13  Persistence, Bioaccumulation & Biomagnification  DDT: falcons, pelicans. bald eagles, ospreys, and many other birds are very sensitive. Thin shells = chicks die.  1972 – DDT banned. Bird reproduction increased.

14  3 characteristics:  Persistence = natural decomposers haven’t yet evolved ways to degrade synthetic pesticides, so they accumulate in the environment.  Bioaccumulation / Bioconcentration = buildup of a persistent pesticide in the body (usually fatty tissues)  Biological Magnification / Amplification = those higher on the food chain have higher conc. of pesticides stored.

15 STORY TIME! WHO’s Operation Cat Drop

16 Mobility in the Environment  Pesticides tend to move through soil, water, & air, sometimes long distances.  Wash into rivers & streams to harm fishes (death or other health problems like bone degeneration).  14.1M US residents drink water w/ traces of 5 common herbicides, causing slightly elevated cancer risk  Air mobility causes problems as well.

17 Short Term Effects  Mild poisoning: nausea, vomiting, headaches  More serious: permanent nervous system damage or other organs.  Globally: more than 3M poisoned, 220,000 die each year.  Worse in Developing nations – no safety training & lax laws.  Bhopal (India) Disaster – methyl isocyanate gas explosion. Converted to hydrogen cyanide (deadly) in the air.  2500 died, survivors had serious respiratory, ophthalmic, intestinal, reproductive, and neurological problems. Survivors were paid $500 each. Cleanup still needs to be addressed.

18 Long Term Effects  Can cause cancer (lymphoma, leukemia, brain/lung/testicle/breast)  Sterility possible.  Higher rates of miscarriage  Greater risk: children of ag.workers (birth defects/stunted limbs)  Immune system suppression  Potential link to Parkinson’s.

19 Pesticide & Endocrine Disruptors  Reproductive problems in animals (endocrine disrupters)  River Otters: abnormally small penises  Female sea gulls: behavioral changes – pair with other females.  Our Stolen Future = 1996 book by Colburn/Dumanoski/Myers  Suggested human hormone systems may be disrupted, as well as other health problems (breast/testicular cancer, male birth defects, low sperm counts).  Cause-Effect relationship still not established.  Should DDT be banned immediately worldwide??  May internationally ban 9 pesticides suspected of endocrine disruption.

20 PROS/CONS of DDT   Research the pros & cons of DDT   Research the ban on DDT by the World Health Organization   Make a list of arguments for & against a potential worldwide ban on DDT.   We’ll discuss next class.

21 Pesticides & Children  Household Pesticides greater threat to children  Play on floors/lawns w/ more pesticide exposure.  Bodies still developing  May cause brain cancer & childhood leukemia.  EPA estimate: 84% of US homes using pesticide products.  Pest strips, bait boxes, flea collars, bug bombs, etc.  Pesticide residue on food  May affect dev.of intelligence & motor skills of young children.

22 Cultivation Methods  Interplanting = alternating rows of different plants  Strip Cutting = harvest one crop at a time, leaving habitat for natural predators of the pests.  Planting around margins to keep habitat for natural predators.  Proper timing & crop rotation

23 Genetic Controls  Create a pest-resistant crop by crossing pest- resistant plants w/ non-resistant.  Problems: fungi/bacteria/pathogens evolve quickly = must keep ahead!  Genetically Modified (GM) Plants can be created quickly ! It could harm other parts of the environment  !  Many varieties are selective. Modify the gene = more general & more widely effective!

24 Biological Controls  use naturally occurring disease organisms/ parasites/ predators to control pests.  >300 species have been introduced.  Careful that new control agents don’t become pests! (weevil/thistle)  Bt = soil bacterium that’s a great natural insecticide.

25 Quarantine  restrict import of exotic plants/animals that may harbor pests.  Effective, but not foolproof.  Ex: Mediterranean Fruit Flies (medflies) in California… it’s worked, but they keep coming back!

26 Pheromones & Hormones  Pheromones = natural substances produced by animals to stimulate a response within their species.  Use to lure insects into traps!  Hormones = natural chemicals produced by insects to regulate their own growth/metamorphosis.  Given at wrong time: abnormal development & possible death.

27 Integrated Pest Management (IPM)  Combine many methods of pest mgmt.  Pesticides are a last resort, and weak ones are used in low amts.  Important for Sustainable agriculture.  Used to MANAGE, not ERADICATE.  Determine when pest pop reaches an economic injury threshold when benefit of taking action exceeds cost.  Requires education on good strategies.  Overall, IPM use is low. Knowledge to use pesticides is less than to use IPM.

28 Reproductive Controls  Sterile Male Technique = sterilize males w/ radiation or chemicals.  Disadvantages:  Must be done continually to be effective - if discontinued, pest pop will rebound very quickly.  Expensive! $$$$$$

29 Irradiating Foods  Use ionizing radiation (gamma rays from cobalt 60) on harvested food to kill harmful microorganisms  First used in US: 1992  Controversial, yet mostly safe.  Can cause free radicals (carcinogenic), but they normally occur produced by frying and boiling.  Don’t know the long-term effects yet.

30 FOOD, DRUG, and COSMETICS ACT (1938)  Recognized the need to regulate pesticides found in food  NO MEANS FOR REGULATION!  Made more effective in 1954: Pesticide Chemicals Amendment (AKA Miller Amendment) required establishment of acdeptable and unacceptable levels of pesticides in food.  Delaney Clause (1958): no substance capable of causing cancer in test animals or in humans would be permitted in processed food.  Didn’t cover raw foods, & lacked data on older pesticides.  Almost impossible for newer pesticides to pass standards

31  Federal Insecticide, Fungicide, and Rodenticide Act  (1947): regulate effectiveness of pesticides (restrict use of ineffective pesticides).  Now requires testing and registration of active ingredients  Don’t meet FDCA standards? No registration with FIFRA.  1972: EPA gets regulatory authority, and has now banned or restricted use of many chlorinated hydrocarbons (DDT)  Amended FIFRA in 1988 to require registration of older pesticides, so now must face the same standards of new pestic.  Didn’t address groundwater cont., establish standards for residues on food or farm worker safety, require companies to disclose potentially harmful inert ingredients

32 Food Quality Protection Act  1996: amended FDCA & FIFRA.  Established identical pesticide residue limits for raw produce and processed foods.  Must consider child susceptibility when considering pesticide residue limits.  Must set limits for all health risks, not just cancer.  Must test for endocrine-disrupting properties.


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