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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