Umm negative.. ive dived this sinkhole, i even went below the hydrogen sulfide layer and lived to tell about it.. the only thing i noticed about my gear was all the titanium and aluminum parts had been turned slightly brownish black. still shiny just with a little tint to it.i noticed no ill effects even though i spent at least 10 min in and below this layer.as far as diving experiences, it rated an epic 11 on my 0-10 coolness scale. also not shown are the amalites (sp?) that are fossilized in the ancient coral walls that form the collapsed cavern.A definite must do if in the tulum area of Mexico. but don't show up with your basic open water, due to the depth, this is for advanced or deep specialist divers only. If you are trimix certified its a blast to go deep below the smog layer. the floor of the cave forms a cone shape with the peak of the cone sticking out of the top of the smog.