Don't confuse "sustainable" with "organic". An organic label means that the food was grown or raised without the use of synthetic chemicals (but there are exceptions).
Lots of people confuse sustainable agriculture with organic farming. Both are aimed at using more ecologically sensible practices, but they are judged by a distinct set of standards.
Organic farming, especially when carried out on a large, industrial scale, can still damage the environment and threaten public health in a variety of ways: Ecosystems can still be ruined by widespread monoculture; pesticides can still be applied; soils can still be depleted of nutrients and organic matter; pollution can still be created; and exorbitant amounts of fossil fuels can still be spent (and wasted), all under an organic label.