Question

2. Half-life is the time required for half of an amount of a particular compound to degrade (see table below). The half-life of DDT in the soilis from 2 to 15 years, and the half-lite of DDT in an aquatic environment is 150 years. 1 half-life 2 half-lives 3 half-lives 4 half-lives 5 half-lives 50% degraded 75% degraded 88% degraded 94% degraded 97% degraded a. If the original concentration of DDT in the water is 2 ppm, how much DDT be remaining in the water after 150 years (1 half life)? (0.5 pts) b. To reach a degradation of 97% (where only 3% of the original DDT is le ecosystem) will take 5 half-lives. How many years is this for DDT in the 8 years as the half life for soil) and how many years is this for DDT in a environment? (1 pt) • Soil: • Aquatic: 15 AM

Answer 1

a) The original concentration of DDT in water is 2 ppm.

Half life of DDT in water is 150 years. This means the amount of DDT reduces to half in 150 years. So after 150 years the concentration also reduces to half its previous value, which is 1 ppm.

So, the DDT remaining in water after 150 years will be 1 ppm.

b) It takes 5 half lives to reach 97% degradation.

The half life of DDT in soil is taken as 8 years in this case.
Five half lives is equal to 5 x Half life of DDT in soil, which is 5 x 8 = 40 years

The half life of DDT in aquatic environment is 150 years.
Five half lives is equal to 5 x Half life in aquatic environment, which is 5 x 150 = 750 years.

To reach a degradation of 97% (Where only 3% of the original DDT is left in the system) it will take 40 years in soil and 150 years in aquatic environment.

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