It depends on the vegetable or fruit. The thinner the skin and more juicy the interior, the more likely that the entire fruit or vegetable has absorbed the chemical. Things like peppers and strawberries are very much prone to absorbing things like Roundup while they are growing. So are leafy greens. If it has a thick skin or is something like onions or garlic, it's not prone to insect predation, so no need to buy organic, but much of our produce is actually full of chemicals. Roundup is just less bad than DDT. The best way to avoid having to use pesticides is to grow plants that insects hate close to those plants that they love and to add plenty of ladybugs to your garden.