Q: For many years I have been using pesticides on my lawn. Now I want to have a vegetable garden, but I am afraid that the chemicals may still be in the soil and would get into the vegetables that I am growing. Are they still in the soil?
A: I have good news for you: almost all pesticides are chemically organic in origin. Organic molecules are decomposed at different rates by sunlight, water and soil microorganisms, but decompose they do. Banned chemicals, like chlordane and DDT, take a long time to disappear, but they do go away eventually. Their long life was a problem, because they accumulated in living creatures and affected their health. Modern pesticides decompose faster. They are designed to do so in order to lessen the possibility of accumulation in the soil and in living things.
Chlordane, once widely used as a termiticide, has a half-life of 4 years, while deltamethrin, a common modern insecticide, has a half-life of 1 – 2 weeks. You can read about the environmental fate of most pesticides at Pesticide Information Profiles.
My bet is that you have little detectable pesticide residue in your soil, but if you want to be absolutely sure, you can remove a three inch layer of soil and replace it with good dirt before planting.