I read an article about an organic strain of vegetables that had been bred to be naturally resistant to certain pests. The idea was that if the plant was "naturally" resistant, the farmers would not have to use pesticides.

When the vegetable strains were analyzed to determine what made them naturally resistant to the insect pests, it turned out that they were now internally producing high levels of a known carcinogen that were absent from the regular "non-naturally resistant" strains. As a result, the organic strains were far more dangerous health-wise than the non-organic strains that had been treated with low levels of pesticides.