The trouble with DDT and other chlorinated hydrocarbons is that they are fat soluble. What this means is that when an organism eats anything that has been sprayed with chlorinated hydrocarbons it stays in their system for a very long time. Consequently, anything that eats that organism also ends up contaminated with the chlorinated hydrocarbon and so on and so forth up the food chain. Humans not only consume vegetation, but also animals that could have eaten that vegetation, so we are particularly susceptible to becoming contaminated by chlorinated hydrocarbons. As if that were not enough, mothers can also transfer chlorinated hydrocarbons to their offspring via breast milk.
Measurable amounts of DDT residues may be found in air, soil,water and at several thousand of kms from the point where it had originally entered the ecosystem. For instance if DDT enters a pond, lake ,it is taken as such by the plants of the pond, then reaches to zooplankton feeding on plants, then to minnows eating the zooplanktons,then to fish which eats the minnows and finally in the body of birds who eat the fish. The chief air pollutants are chlorinated hydrocarbons. They have carcinogenic effects on lung. They combine with NOx under UV-component of light to form other pollutants like PAN and photochemical smog which cause irritation of eye, nose and throat, and respiratory distress.