I have never heard of that before!
I have a step-daughter who is potty training and never heard it was a bad thing when I was pregnant....its human urine just like ours, I don't see a difference with toddler urine and adult urine.
I know that being around cat litter and areas that they urine etc. you shouldn't be around that. She may have misheard the person, or else the instructor doesn't know and just said that for the hell or it!
I'm sure not to worry!!
I have never heard this before. You might want to post this in one of the expert forums and see what they say....