DDT

DDT and Marine Organisms

What is DDT?

DDT was widely used in the 40's and 50's as a pesticide until it was outlawed in the 70's. However, now DDT is often used illegally. It is a synthetic organic chemical. Like many other synthetic organic chemicals, DDT is very persistent. It collects in the fats of organisms and is not metabolically broken down so therefore its effects can be passed through the food chain, an example of biological amplification.

A diagram depicting the organisms affected and biological amplification.

Who does it affect and in what ways?

Microorganisms

Marine microorganisms like plankton and green algae are greatly affected by DDT because an aquatic environment can bring more DDT in contact with these organisms. It can slow down growth and photosynthesis in green algae. However, most microorganisms do not usually die from this chemical. They keep the DDT within themselves, but being the base of the food chain, other organisms are also affected.

Aquatic Invertebrates

Terrestrial invertebrates are not affected very much by DDT, but aquatic invertebrates, especially in juvenile forms are very sensitive to the chemical. So effective against aquatic invertebrates, DDT was used to control sea crustaceans. Aquatic invertebrates when faced with DDT, can have reproductive and devolpement impairment and nervous system disorders.

Fish

It has been difficult to study DDT in fish because the chemicals cause so many problems. Although it is uncertain exactly here DDT does the most damage, it probably involves the chemical's presence in the fish's plasma membrane. Studies do show that smaller fish are usually more sensitive to DDT.

Birds

The adverse affects of DDT are well known in birds. It affects ospreys, eagles, pelicans, falcons, and hawks.

The Brown Pelican nearly went extinct due to the usage of DDT. It was discovered on the Anacapa Islands off Southern California, the hatching grounds, that few pelicans were surviving. The eggshells were paper thin and very few pelicans were being born. In the 1960's, scientists found high concentrations of DDT in the Brown Pelicans' blood. In 1969, 750 nests were found, but only 4 chicks were born. In 1970, there were 550 nests and one chick survived. DDT was then outlawed and the numbers of Brown Pelicans revived.

A Brown Pelican

To read a theory on the eggshell thinning.

How does DDT kill?

DDT disrupts the working of a cell. It affect the plasma membrane. The plasma membrane separates the inside of the cell from the outside, allows substances to enter and leave the cell, and is made of lipids(fats). DDT is fat soluble, so it dissolves into the plasma membrane but, at the same time, opens up the membrane causing the cell to leak. Potassium ions and sodium ions slip through the membrane. In a nerve cell, these ions will help determine when the cell will fire its signals. Nerve impulses tell the muscle when to contract and relax, but with DDT present, nerve impulses do not fire when they are supposed to. DDT results in the organism's death through convulsions(random uncontrolled contraction of the muscles) of by paralysis(complete loss of muscle control).