Effects of Chemicals on Organisms:
Effects of Chemicals on Organisms:
Many chemicals are used in industry, in agriculture, and in our homes. These chemicals can be helpful; however, some are harmful to humans, other organisms, and the environment.
DDT and the Environment
• Chemicals developed for a specific purpose can have negative effects on the environment.
• Often the effects of chemicals are not known until they cause a serious problem, like with the example of DDT.
• DDT (dichlorodiphenyltrichloroethane) is very effective in killing mosquitoes that cause malaria, and it saved millions of lives.
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• However, its use was discovered over 40 years later (in 1972) to also harm the environment and has since been banned in the US.
• Why did it take so long for people to recognize that DDT causes serious environmental problems?
• The effects of a chemical on organisms depend on factors such as dose, potency, exposure time, individual susceptibility, and concentration.
Dose
• The dose of a chemical substance is the amount that is given to one individual.
• Sometimes the appropriate dose of a chemical is not well understood.
• With DDT, the chemical was sprayed over wide areas, so it was impossible to know what dose of DDT and how much a single organism had absorbed.
Potency
• The potency of a chemical refers to how powerful it is.
• Any drug that produces a visible or measurable effect at a low dose is said to have a high potency.
• Scientists decide the potency of a drug using a toxicity test.
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• DDT’s potency in the environment could not be determined because no one knew how much of the chemical any single organism was exposed to.
Exposure Time
• The exposure time is how long an individual is exposed to a chemical.
• Determining the exposure time is not always simple because the stability of chemicals varies.
• DDT is very stable and remained in the environment for a long time, resulting in the continual exposure to DDT after its use had stopped.
Individual Susceptibility
• Individual organisms respond to chemicals in different ways.
• Individual susceptibility depends on the physical and genetic make-up of an organism.
• An individual who is overweight, eats fatty foods, and has a family history of heart disease is more susceptible to heart disease than a person who is at a healthy weight, eats healthy foods, and has no family history of heart disease.
Concentration
• A chemical’s concentration refers to the amount of a substance in a given volume.
• Calculating the concentration of a chemical in the environment is difficult because many factors affect how far a chemical will spread.
• As a result, it is not possible to know the volume (space) that the chemical occupies.
• After DDT had been sprayed in the environment, it slowly seeped into ponds, streams, and other bodies of water.
• Small organisms took in DDT but were not immediately affected because the chemical was not concentrated in their bodies.
• Fish then ate these small organisms, and DDT became more concentrated in the fish.
• DDT concentration levels increased as it moved up in the food chain.
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Review Questions:
& Coach p. 224, 1-3
1. How can concentrations be increased or decreased?
- By increasing or decreasing the amount (dose) of a given substance or by increasing or decreasing the total volume.
2. How would an increase in DDT concentration on a specific corn field affect the potency of the chemical?
- An increase in concentration in DDT would increase the potency, making it stronger.
3. Predict how changes in exposure will decrease or increase the susceptibility of the individual.
- A shorter exposure time would decrease the individual’s susceptibility of negative effects of the chemical and vise versa.
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