Unless you buy organic grain, or raise it yourself, ALL grain has been farmed using chemicals, so yes, there may be some chemical residues in it. But that is true of all the grain products you buy at the grocery store, cornmeal, bread, flour, etc. If it isn't organic, you are getting some farming chemicals in your diet. It probably won't kill you soon, anyway, and having some food, even non-organic, is probably better than starvation.
The grain you buy at the feed store will not have been treated like non-organic seed corn, however, as it is assumed that it will be consumed by critters rather than being planted. Non-organic seed corn (corn you buy specifically as seed) has been treated to help prevent disease issues when planting, particularly with early planting in cool, damp soil which is the modern preference.
It comes in feed sacks, which are something like dog food bags if you are familiar with those. Sacks like that are susceptible to rodents, of course. And sacks like that are not for really long term storage, as they are not impervious to oxygen. So, if you want to store this away long term, put it in buckets, and deal with it as you would wheat - the bags and oxygen absorbers, etc. would be helpful to extend its storage life. If you intend to start using it immediately and to convert your diet to eat out of storage (at least in part), and if you are able to store it somewhere where there are no rodent issues, then you don't have to get so extreme in your storage method.