I have never heard of eating parsnip leaves, so I Googled it and found from The National Vegetable Society ....
"Parsnip leaves can be blanched in spring and used in salads as you would use celery. Simply draw soil over roots that are sprouting."
BUT, from The Two SmallFarms Newsletter
Issue Number 270 - March 31st , 2004
"In fact, parsnip leaves are toxic
and exude natural chemicals called furocoumarins.
These toxins can provoke an irritating rash
somewhat like poison oak if you get them on your
skin or rub them in your eye. The roots don t carry
the furocoumarins at all, but you will notice you
never see bunched parsnips in the supermarket"
So you takes your chances it seems !
Disclaimer: I almost certainly haven't a clue what I'm talking about.