for a bowl (either bong bowl or pipe) GREATLY depends on where the cracks are...

anything anywhere near where all the bud goes, or direct flame touches (or gets close to) time to get a new one....

however if say the mouthpeice of your pipe broke, or, the bowl/stem broke like half way down the stem.... superglue or epoxxy should work...

sorry dude there's not to terribly many 'glues' that will work to substantially to repair glass peices without it falling to peices again in a week or so.. and i know of absolutely none that are non-toxic.. atleast when heat comes into play... however, most epoxxy's and glues will be non-toxic just breathing in after a 24 hour cure (drying)

using superglue and trying to smoke 20 mins later could def. be toxic... so you understand what i mean by how it goes non-toxic durring curing...

and almost any glue out there, can very well be toxic if it gets super heated or burned.