《环境化学》课程PPT教学课件讲稿（英文版）Unit 19 Pesticides

Pesticides

Pesticides

Pests and pesticides Pest: ANY UNWANTED organism that directly or indirectly interfere human activity is called a pest. o Pesticides or biocides are substances that can kill organisms that we consider to be undesirable The most widely used types of pesticides Insecticides Herbicides Fungicides Rodenticides

Pests and pesticides • Pest: ANY UNWANTED organism that directly or indirectly interfere human activity is called a pest. • Pesticides, or biocides, are substances that can kill organisms that we consider to be undesirable. • The most widely used types of pesticides: – Insecticides – Herbicides – Fungicides – Rodenticides

Reasons for our use of pesticides Insects compete with us for food It is estimated that 30% of agricultural crops are consumed by insects worldwide Swarms of locusts like this one in morocco can completely destroy crops

Reasons for our use of pesticides • Insects compete with us for food: It is estimated that 30% of agricultural crops are consumed by insects worldwide. Swarms of locusts like this one in Morocco can completely destroy crops

Reasons for our use of pesticides Some insects are diseases carriers Disease Disease carrier Malaria Anopheles mosquito Bubonic plague Rat fleas Typhus Body lice and fleas Sleeping sickness Tsetse fly

Reasons for our use of pesticides: Some insects are diseases carriers Disease Disease carrier Malaria Anopheles mosquito Bubonic plague Rat fleas Typhus Body lice and fleas Sleeping sickness Tsetse fly

The ideal pesticides Kill only the target pest Have no short- or long- term health effects on non-target organisms, including people Be broken down into harmless chemicals in a fairly short time Prevent the development of genetic resistance in target organisms Saving money compared with making no effort to control pest species

The ideal pesticides • Kill only the target pest • Have no short- or long- term health effects on non-target organisms, including people. • Be broken down into harmless chemicals in a fairly short time. • Prevent the development of genetic resistance in target organisms. • Saving money compared with making no effort to control pest species

The case for ddt H|c|c|c DDT Para-dichlorodiphenyltrichloroethane

The case for DDT C H C Cl Cl Cl Cl Cl DDT Para-dichlorodiphenyltrichloroethane

DDT: an almost ideal pesticide Chemically stable and degrades slowly Each application is Low volatility effective for a long Low solubility in water me Readily penetrates the waxy coating of insects Low toxicity to animals, including human beings Ddt binds to the nerve cells of insects> hold open the molecule channels for sodium ions>uncontrolled firing of the nerves> kill the insects

DDT: an almost ideal pesticide • Chemically stable and degrades slowly • Low volatility • Low solubility in water • Readily penetrates the waxy coating of insects • Low toxicity to animals, including human beings. Each application is effective for a long time DDT binds to the nerve cells of insects → hold open the molecule channels for sodium ions → uncontrolled firing of the nerves → kill the insects

The minus side of ddt: bioaccumulation Example: Accumulation of ddt in the aquatic food chain coT in tish-eating tiras csp'eys 分 DDT in large Chemical basis for fish(needle fish) bioaccumulation DDT is more concentraion ascreased DDT in sma t0 malon ' imes fish (minnows) soluble in fats 0.5 ppm than in water. 004pm DDT in water 0.00003cpm

The minus side of DDT: Bioaccumulation Example: Accumulation of DDT in the aquatic food chain Chemical basis for bioaccumulation: DDT is more soluble in fats than in water

DDT and mosquito-lizard-cat connection DDT spraying for malaria eradication Example: Accumulation of Killed mosquitoes killed cater-pillar eating DDT in the food as intended wasps-unintended chain on land Dead mosquitoes Fewer wasps led to sickened an explosion of gecko lizards cater-pillar population Sick lizards poisoned local cats Cater-pillars consumed thatched roofs Fewer cats led to an explosion of the rat population Rats ate local crops and threatened an outbreak of bubonic plague

DDT and mosquito-lizard-cat connection DDT spraying for malaria eradication Killed mosquitoes as intended killed cater-pillar eating wasps-unintended Dead mosquitoes sickened gecko lizards Sick lizards poisoned local cats Fewer cats led to an explosion of the rat population Rats ate local crops and threatened an outbreak of bubonic plague Fewer wasps led to an explosion of cater-pillar population Cater-pillars consumed thatched roofs Example: Accumulation of DDT in the food chain on land

The minus side of ddt use The accumulation of DDT inside birds tissue disrupts calcium control mechanism during egg formation. The egg shells are so fragile that they crack and do not survive until hatching

The minus side of DDT use The accumulation of DDT inside birds’ tissue disrupts calcium control mechanism during egg formation. The egg shells are so fragile that they crack and do not survive until hatching