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 soil is from 2 to 15 years, and the half-life of DDT in an aquatic environment is 150 years.

1 half-life	50% degraded
2 half-lives	75% degraded
3 half-lives	88% degraded
4 half-lives	94% degraded
5 half-lives	97% degraded

a. How many years have passed after five DDT half-lives in an aquatic environment?

b. If the original concentration of DDT in the water is 2 ppm, how much DDT would be remaining in the water after 1 half-life?

c. How much DDT would be remaining in the water after 5 half-lives?

3. Do you think DDT has the potential to cause more long-term harm to an estuary ecosystem or a terrestrial (on land) ecosystem? Why?

Answer 1

2.

a. 1 half life = 150 years

therefore for the completion of 5 half lives it will take 750 yrs

b. After 1 half life 50% is degraded

then 2 ppm DDT's 50% will be 1 ppm

so 1 ppm will be remaining

c. After 5 half lives 97% of DDT is degraded

then, 97% of 2 ppm DDT will be will be 1.94 ppm

so the remaining DDT will be 0.06 ppm

3. Yes DDT can cause long term effects. Because;

1. In case of estuary ecosystem: Estuary is the transition zone between river environment and marine environment. Here due to the mixing of seawater with fresh water, it provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world and its banks are among the most heavily populated areas of the world, with about 60% of the world's population living along estuaries and the coast as well as seasonal variation in their fish communities and migratory bird communities too. So DDT from this place can not only impact river ecosystem but also land and marine ecosystem which will lead to a long term diverse impact.

2. Terrestrial ecosystem: DDT has already proven to cause a huge impact on the land ecosystem and more it accumulates it will lead to more long term impact as it does not degrade easily in a short period of time. It will accumulate in various trophic levels and will result in death of many animal populations which will disturb the normal functioning of the ecosystem and increase in the incidences of other infestations resulting in huge damage.