This Harleygyrl should stick to motorbikes on which she is surely an expert. The notion that selenium is a chelator is oversimplistic on several fronts. Firstly selenium can mean different things (inorganic, organic, se-yeast, and more). Secondly, the problem with chelators such as DMSA and ALA is that they are very poor chelators, they'll take it out from your fillings then dump it in your body (or in respect of ALA move it into your brain).
By contrast, selenium is rumoured to bind very strongly. And more to the point, it is a most important nutrient. Much of the problem of merc is that it inactivates Se. You need a lot more Se to compensate for that, it is the most important "antidote". I find that the only way I can suppress my symptoms (of merc coming out of brain and trashing body not least photophobia) is with 2000mcg SeMeth a day. Avoiding Se is a sure way to avoid health. But some forms such as selenate selenite are not what you need and could indeed cause negatives. Alternatively Laurenbird's comment may be a false positive coincidence and she just has jumped to a conclusion too soon.