yes
death
Eutrophication
To little and bacteria can thrive, to much and it can be harmful to the body.
. eutrophication
Yes, it's toxic. You could die if you had too much
Yes. Too much sodium, for example, can lead to elevated blood pressure and heart disease.
Nitrogen is a fairly inert gas that has no harmful affects unless it is found in too high of quantities. This would cause oxygen deprivation. It would be a bad idea to enter a pure nitrogen environment.
What a stupid question... Everyone knows that Vitamins which are not used will come out...
spotting after heavy exercise means you are stressing your body too much , the bleeding itself is not harmful as it is not much but your body is under too much stress. you should listen to your body signs. I recommend you to reduce your exercise a little and see if the spotting finishes.
eutrophication
Yes. Too much of ANYTHING can be harmful. The entire universe runs on the Goldilocks principle; too much, not enough, or just right.