In the last section, we learned how DDT can kill organisms by interfering with the plasma membrane. Here, we learn some of the specific effects it has on certain organisms:

microorganisms
invertebrates
fish
birds
mammals
human beings

Microorganisms:

Even small amounts of DDT can affect small microorganisms. This is especially true for microorganisms that live in the water (i.e. algae, and plankton), because the aquatic environment can bring more DDT in contact with these organisms.

As an example of this high sensitivity, water that contains only 0.1 (g (micrograms) of DDT per liter can slow down growth and photosynthesis in green algae.

To get an idea of how dilute this water is, think about a paper clip, which weighs about one gram. Take that mass, and divide it by TEN million! Let's say that this tiny amount of DDT was dissolved in a quarter gallon of water. Remarkably, microorganism growth will be affected because of this!

Although affected by DDT, the microorganisms do not usually die. Instead, they tend to keep the DDT within themselves. Considering that microorganisms such as green algae and plankton form the basis of the food chain, how do you think other organisms affected by this?

Invertebrates:

Terrestrial Invertebrates (backbone-less creatures that live on land; examples include molluscs and earthworms) are not affected very much by DDT. In fact, they can tolerate a lot of DDT for long periods of time.

They will, however, retain a lot of the DDT in their bodies (accumulation). This makes it dangerous for those predators who eat these organisms (biomagnification).

Unlike their land-loving relatives, aquatic invertebrates are quite sensitive to DDT, especially while these creatures are still very young. Some problems associated with DDT include reproductive/development impairment and nervous system disorders. At one time, DDT was used to control certain sea crustaceans, because it was so effective against these aquatic invertebrates.

Fish

DDT causes many problems in fish (So many, in fact, that it has been difficult to study DDT in fish. We can't seem to find where the DDT is doing the most damage.) We think that problem probably involves DDT's presence in the fish's plasma membrane, an area where important biological processes are occuring.

There are a few trends that we've noticed with DDT and fish. Smaller fish are usually more sensitive, and for same species of fish, DDT becomes less toxic at higher water temperatures.



Birds

DDT is most famous for its effect on birds. Some research have shown that for certain species, DDT causes the thinning of eggshells.

Some species affected by DDT:
osprey
eagles
pelicans
falcons
hawks

(For a possible explanation to eggshell thinning, click here.)

Mammals

In the past, we have used DDT to control mice, rats, and bats.

Bats are especially sensitive to DDT. Very low doses of DDT can affect them severely. (For an explanation to the high sensitivity in bats, click here.)

A lot of current research deals with DDT's effects on larger mammals.

Human Beings

In the early to mid 1950s, DDT became one of the most widely used pesticides. This was when we thought it was completely harmless to human beings. When we originally used it to control lice, people were unaffected even though they were in direct contact with the pesticides.

One of the reasons why the DDT did not affect people is because it is difficult for DDT to be absorbed through human skin.

Eventually, we realized that some DDT was staying in our bodies. DDT was being used in the environment, on agricultural products, and on livestock. In the 1960's, concern arose about the widespread use of DDT and it's effects on humans.

A study in 1968 showed that Americans were consuming an average of 0.025 milligrams of DDT per day!

When DDT gets into our bodies, it is stored primarily in such fatty organs as the adrenals, testes, and thyroid. DDT is also stored in smaller concentrations in the liver and kidneys.

DDT concentrations are especially high in human milk. Milk production depends heavily on the use of stored body fat, and this is where DDT tends to stay in our bodies.

So exactly how much DDT can my body tolerate before I should really start worrying? That depends on how much you weigh. At concentration above 236 mg DDT per kg of body weight, you'll die. Concentration of 6-10 mg/kg leads to such symptons as headache, nausea, vomiting, confusion, and tremors.

For fun, try and calculate how much DDT would be lethal for you.

Currently, there is much debate as to whether DDT can increase a woman's chance of breast cancer. Apparently, some researchers are saying that DDT (and some of its related forms) is an estrogen mimic. (For an in depth discussion of estrogen mimics, click here.)


This completes the Dangers of DDT.




Return to the beginning of the Pesticides unit.