I don't have a shortage of browns. I shy away from cardboard because I worry about the inks. I don't know much about inks outside of domestic newspapers using soy to get away from haz mat handling issues.
I suppose food packing boxes should be safe.
I'm not overly sensitive since I do use shredded office paper which comes from photocopiers and laser printers which means toner. Toner is essentially a non-toxic plastic. To paraphrase the response I got from Xerox: the paper will break down but the toner will not.
I can get shredded paper and don't have to shred cardboard so it's an easy decision.
I'd look out for anything that might be printed overseas.