Organic or not?

Pesticide residues are found in the flesh of fruits and vegetables, not just on the exterior--some foods are more susceptible to retaining residues than others.

Although many pesticides are initially sprayed on the surface of the plants, they are eventually rinsed off by rain or irrigation; they then flow into the soil and are absorbed by the plant’s roots.  Some “systemic” pesticides are applied directly to the soil, and not to the surface of the plant at all.  There are also gas “fumigants,” which can be applied after harvesting to help speed up ripening and to control rot and hard-to-kill pests; they generally need to penetrate the plant material deeply to be effective.

[[MORE]]“Organic” is not the same thing as “pesticide free.”  Many organic foods still use pesticides, although the ones used are generally considered to be “less toxic” (whatever that really means), and the detectable residues are generally lower than in conventionally grown food.  In fact, even food labeled “pesticide free” often isn’t free of residues (unless it’s labeled as No Detectable Residue [NDR]), due to drift and residues from previous crops in the same fields.  That’s yet another reason to grow (or raise) some of your own food, or to buy from a local farmer you trust, if you can.

Here’s a link to a paper with some details:
http://www.consumersunion.org/food/organicsumm.htm