Thank you for your concern, cause I am one of the fellows that use a 5 gal pail from Walmart.
If you do use a 5 gal pail do your homework. On the bottom of the pail should have the manufacture address and phone number (and maybe a lot number). My pail was manufactured by Encore plastics in Byesville, OH. I was curious about the grade quality of my bucket so I searched their website.
Cam across this page: http://www.e-encore.com/FAQpolyethylene.html
Second question down states that my pail (HDPE) is FDA approved.
Some risks are greater than others, but the only risk I have from my pail is my growing waist line. (God I hope it isn't a tumor.....)