1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane. That's the scientific name of DDT. (Thankfully, most people don't use the full name!) DDT's chemical formula is C14H9Cl5. So, for every molecule of DDT, there are 14 carbon atoms, 9 hydrogen atoms, and 5 chlorine atoms. Here is a picture of a DDT molecule. In its pure form, DDT is a white, crystalline powder with little odor. (So, it's somewhat like table salt.) One of the reasons why we worry about DDT is because it doesn't break down in the environment or in organisms. DDT's long life is due to its low solublility in water and it's relatively high solubility in fats. Solubility is the ability for one substance to completely dissolve in another. DDT is water insoluble and lipid (fat) soluble. This means that DDT will not dissolve in water, but it will in the fats of organisms. CHEM WINDOW - Solubility Since DDT is insoluble in water, it is difficult to wash away in the environment. (Have you ever watched news coverage of an oil spill? Petroleum, like DDT, is also insoluble in water. Did you notice how difficult it was for the workers to get all the oil off the animals?) On the other hand, DDT is soluble in lipids (fats). This means that once an animals ingests a little DDT, it will mix in with its fat. And as we all know, all organisms (including human beings) have a certain amount of residual fat in their bodies. Once DDT get in there, it tends to stay. Why doesn't DDT get flushed out of the body by dissolving into the blood? Because DDT stays in the body, it can build up in the body if the organism continues to eat food with DDT. This build-up of DDT is referred to as accumulation. Thankfully, accumulation will not continue forever. There comes a point at which no more DDT will be retained within an organism. We can say that DDT has been saturated in the lipids of the organism, and any more of it will not dissolve. A practical example of saturation: Have you ever tried mixing sugar in water? After a certain point, no more sugar will dissolve, even with lots of stirring some sugar stays in the bottom of the glass. The water is now saturated with sugar. Accumulation leads to another problem with DDT. This is biomagnification, which occurs when DDT becomes more concentrated as you go up the food chain. This means that animals on top of the chain can potentially have the highest concentrations of DDT. And remember, human beings are on top of the chain! CHEM WINDOW - Biomagnification This completes the Physical and Chemical Properties of DDT. Return to the beginning of the Pesticides unit.