Pests and Pesticides
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Any substance used for controlling preventing, destroying, repelling, or mitigating any pest
- insects, mice, and other animals
- Unwanted plants
- Fungi or microorganisms like bateria and viruses
Classes of Pestcides
- An organism which transmits a disease, primarily to humans
- Many Public Health and Pesticide campaigns directed at controlling disease vectors
- Mosquitoes are probably responsible for more human deaths than any other insect
- Ingested poisons
- Contact poisons
- Fumigants (respiratory)
- Organic- contact poisons, broad spectrum, chlorine-containing, OPs
- Inorganics- Heavy Metals
- Chlorinated hydrocarbons- persistent in the environment, most banned in the US but we are stile xposed from imported food (examples DDT and Chlordane)
- Organophosphates: not persistant, but toxic
- Carbamates: not persistent, but toxic
- Pyrethroids: relatively safe. Fleas, Ticks
- discovered by Paul Muller in 1939
- Extremely effective at killing insects on contact
- Extremely environmentally persistant: half life in soil 15-50 years, half life in water 150 years
- In WWI more soldiers died from cholera and dysentary than bullets. Foudn use in WWII protecting troops in tropical locatiosn
- Post-WWII DDT found use ina griculture
- Her book Silent Spring, published in 1962, suggested pesticieds were poisoning wildlife and the environment, and endangering human health. She speculaated DDT was enemy #1
- The book was an immediate best-seller and set off the environemntal movement in the US
- In 1967 a group of scientists formed the Environmental Defense Fund, dedicated to banning persistent chemicals
He proved eggshell thinning and decline of bird species was due to DDT. The EDF pushed for an immediat ban on DDT. The EPA refused. EDF filed suit.
- THe stockholm convention placed a permanent worldwide ban on DDT and other persistent organic pollutants, with exceptions for public health use
- DDT is still used today where Malaria is endemic
Some mosquitoes metabolize DDT much faster than others. DDT kills "poor metabolizers" and lets others live. Survivors are then resistant
DDT opens sodium channels in neurons, causing spontanous firings, leading to spasms deaths. Some insects have genetic mutations in channels that make them restant to chemical. Resistant insects survive.
some mosquitoes have "bite-and-run" behanior that allows them to avoid chemcial interaction
Integrated Pest Management
"The most effective strategy, based both on evolutionary models and on evidence, is to proved pest species with pesitcide-free "refuges" in which susceptible genotypes can reproduce, thus preventing resistant genotypes from taking over."
- More widely used than insecticides. They cause plants, in most cases to "grow to death"
- 2,4-D and Dioxin issues. Implicated in breast cancer, brain cancer, miscarriage, many other health effects
- Preplanting: applied to the soil before planting
- Pre-emergents: applied to the soil before weeds germinate
- Post-emergents: applied to the soil or weeds after the crop and weeds have sprouted
Herbicides and Agent Orange
- Agent Orange a mixture of 2, 4-D and 2,4,5-T.
- During the Vietnam war 19 million gallons were sprayed on S. Vietnam
- Agent Orange contaminated with dioxin
- Dioxin is environmentally persistant
- Most are anticoagulants
- Cause internal bleeding. Rats have no cas reflex, they ingest poison and can't vomit.
- Associated with Congenital heart defects in women and children
- Used all over the world for murders, suicides, and accidental poisonings
Current Pesticides Issues
- Death of non-target species
- Environmental persistence, soil and groundwater contamination
- Biomagnification- the poison becomes concentrated as it moves up the food chain
- Migrant worker health and other unidentified health issues from long-term exposures
- FDA continues to "revise" estimates for allowed levels of mercury in the diet: Now, instead of saying how much mercury is safe to ingest, its now expressed as "safe meals/month"
- 1990: three fish meals/weeks
- 1997: 2 fish meals/week
- 2002: tow fish meals/month
- 2009 survey showed that US freshwater fish shwoed measurable mercury in EVERY fish. Only 25% of the fish had levels considered dangerous
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