Toxic materials that enter the body cannot the body cannot always be excreted and be stored in the fatty tissues. Examples include the organochlorines , DDT, PCBs, and chlordane. When a person loses weight, for whatever reason, toxic materials that have been stored in the fatty tissues are released back into the body as the levels of fat decrease. When this occurs, the body is reexposed to the chemicals and illness can occur. Chemicals that cannot be excreted from the body may also be bound by blood proteins and stored in the blood. Lead is an example of a material that cannot be excreted from the body and is stored in the bones.