I would like to make a cutting board from some hardwood I have. I'm pretty sure it has been imported, so I think it might have been fumigated or treated for insects/pests at some point. I've tried researching about this but I found very little, but the little I did find suggested sanding it as the fumigation process would only leave chemicals on the surface. Does anyone have any input? It looks like a good beginners project but I want it to be as food safe as possible.
If you think the wood was treated or fumigated, I wouldn't trust sanding to make the wood food-safe. As another answer notes, wood is porous and could very well have absorbed the chemicals deeper than you'll sand out.
I would definitely err on the side of caution here and only use wood that you know is safe to begin with. There is no finish that you can use on a cutting board that will keep the base wood completely out of contact with the food, due to knives being used on it.
I would recommend starting with hard maple. It makes durable, great-looking cutting boards, and is completely food-safe.
Wood is inherently porous, so the big concern with wooden cutting boards is keeping them relatively sanitary after chopping things like meat and fish on them. Some people use mineral oil or bees wax, although I have personally used coconut oil. Straight cooking oil isn't a good idea because it will go rancid.
One thing that you want to make absolutely sure of is that the wood has not been pressure treated or soaked in any kind of preservatives. If the hardwood was ever exposed or intended to be exposed to outside elements then there is a good possibility that it could be treated with highly toxic preservative chemicals.
My brother is a carpenter, and he would suggest using Salad Bowl Finish (http://www.rockler.com/product.cfm?page=5344) I can personally attest to the fact that it does a nice job - we used it on all the cutting boards in our kitchen.