Mercaptan is non-toxic, and a naturally occurring chemical in things we see and eat everyday. Mercaptan is less corrosive and less toxic than similar sulfur compounds found naturally in rotten eggs, onions, garlic, skunks, and, of course, bad breath. Your bad breath has more toxic mercaptans then my BHO. Mercaptans may be present in certain MJ strains also(see: SKUNK). The refining process for the butane is to remove the waxes. They may not be able to remove it all, The common name for Oleaginous Waxes from petroleum, is Paraffin, which is non-toxic enough to have no known LD-50 data and be used to seal jelly jars, so they are of low concern when extracting. If you are worried about the parafin wax you can winterize and filter out the waxes with pure ethanol (NOT ISO). ISO is toxic, so I would not go around touting ISO as safer than BHO, unless your using pure lab grade ethanol.
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