Pesticides. Hormones. DDT.
Sound appetizing? It shouldn't.
And you should know the difference and importance of choosing foods to eat organic, but also not worrying about others being non-organic. Few things to consider:
1) Domestic versus non-domestic: Any vegetable or fruit from another country MUST be treated with something (usually a waxy residue to keep it's color, flavor locked in), so in most instances, try to buy local, USA produce. It's that simple. This list would include meat and fish.
2) Skin on/skin off: eating anything with a skin and is grown above the ground increases the risk of pesticides and DDT being a part of your meal. Examples below.
3) We are what we eat eats: Michael Pollan (Carnivore's Dilemma, In Defense of Food) has pointed out that our food chain has choices, and so do we. Stick to wild fish and meats (again, USA preferred) that has not taken a 5,000 mile journey to get to your plate, and that has been eating it's natural food sources. For cows, this is grass, and for fish, it's other fish. The main reason farmed salmon, tilapia and other whitefish are horrible is because they are fed a synthetic, colored food in order to help them maintain their natural color and texture.
Here's the list of which foods to eat organic versus not. For more information, check out the book The New American Diet (http://www.amazon.com/New-American-Diet-obesogens-flatten/dp/1605294640/ref=sr_1_1?s=books&ie=UTF8&qid=1299157392&sr=1-1).
DIRTY DOZEN (worst first, eat all the italic foods organic!):
Sweet bell peppers
Clean Fifteen (conventionally grown versions of these items are fine)
Fishes to eat:
Wild Alaskan Salmon
Farmed Rainbow Trout
US Albacore, yellowfin tuna
Chilean sea bass
Here's to clean eating!
Source: The New American Diet, by Stephen Perrine