How would DDT enter a marine ecosystem? If DDT was banned in Canada in the early 1970s, why do animals still carry residues of this toxin? Why might the levels of DDT fall more slowly in porpoise than in other animals in the food chain?

DDT might enter a marine ecosystem through runoff from streams or rivers near places the chemical was sprayed. Animals still carry residues of DDT because it is contained in fat and can be eaten and transferred further along the food chain. Porpoises might be more susceptible to it because they have a layer of fat known as blubber.

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There are several questions being asked here, but I should be able to weave them together in an answer. DDT is an insecticide that was first synthesized in 1874 by a chemist named Zeidler. Prior to being banned in 1972 by the EPA, DDT was used extensively. As an insecticide, it was extremely successful. However, it was banned due to its cancer causing agents and how long it persists in the environment.

DDT persists for a long time in an environment for a variety of reasons. One such reason is that it is fat-soluble. This means that DDT is easily stored in animal fatty tissues, and it can work its way through an entire food web. An animal low on the food chain that was exposed to DDT will be eaten by some kind of predator species. The DDT will become concentrated in the fatty tissues of the predators, and that concentration will be passed on to higher and higher levels of predators. The apex predator will then receive the highest dosage of DDT. This could lead to health complications to that apex predator or any other predator in the food web because fat stores are used for energy during periods of starvation. The breakdown of these tissues releases DDT into the blood, where it becomes toxic to the liver and nervous system.

DDT can enter into an aquatic environment through the simple process of runoff from fields or other places where it was sprayed. Excess DDT can be carried by runoff into stream and rivers that eventually lead into aquatic environments like the ocean. DDT is extremely toxic to both fish and aquatic invertebrates. It can work its way through aquatic food chains into the porpoise populations the same way that it works on land based organisms.

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