Subject: Nitrate fertilizers and the human body

I snuck into an ecology class the other day, and were teaching about the hazards 
of excess fertilizers. Well, I asked the teacher why people are wary of using 
too much fertilizer in the fields. He said that it was to prevent 
eutrophication. Now that doesn't directly affect the human body. 
A vague thought that's dancing somewhere inside my head says I read something 
somewhere that said that nitrates in the diet somehow cause methemoglobenia (I 
KNOW I didn't spell that right). What really happens? How do nitrates from 
fertilizers harm the human body? 

Re: Nitrate fertilizers and the human body