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:
Pesticides Ch 22
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.
“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.
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)
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)
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
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
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.
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.
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.
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.
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.
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.
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.
STORY TIME! WHO’s Operation Cat Drop
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.
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.
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.
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.
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.
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.
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
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!
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.
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!
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.
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.
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! $$$$$$
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.
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
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
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.