Angeleno,  check out the MSDS sheet for sodium thiosulfide.  Section 3,  I think,  is supposed to list health exposure hazards; older MSDS sheets listed a number of concerning dangers for short term effects, none for long term health effects.  I was told by a laughing chemist that they must have all died..  
Also, in my experience, the game was always to claim "proprietary information" for as many ingredients as possible.  In fact the chemical companies supplying the oil field service companies played that game.  So ther were two levels of "proprietary ingredients".
Next.  Your right, fracturing does not cause ground water contamination.  Bad or incomplete cementing of wells does.  That was the real problem on Deep Water Horizon in my opinion.  When producing zones are not properly isolated   the problems come.  In that case, BP should have set a final 'tacked string' not a very small cement squeeze.  And thoroughly tested well integrity.