It's not easy to test the effects, because effects are usually long-term, things like cancer can take decades to be noticed, and "organic food" is quite recent. Remember how long it took to be sure smoking tobacco was really toxic. If I look at France (where I live), the "AB" label for organic food was created in 1985, and it's only recently (maybe a decade, even less) that AB food is available in normal supermarkets. So it's hard to have strong data yet on long-term effects. But I hope they'll come in the next decade.