Ash is very safe for humans and all animals to consume, and it's young leaves are very useful as an early spring vegetable, cleaning out internal parasites and calming from settling down our digestion. Its effect on our digestion is actually much like the theme of my story poem. It generally takes a lot of consumption of Ash to be toxic to humans, though I must still provide my caution here ...

As with all natural remedies consumption of Willow
should be guided by a qualified herbalist or physician.
This information here is for information purposes only,
and certainly not for prescription.

best use ...  

early spring green vegetable and internal parasite cleaner

qualities of Ash are said to be ...

anthelmintic - cleanses parasites and worms
aperient - gentle laxative
bitter - fluid lost through bile, another cleansing and detox action
diuretic - increases urination, useful when clearing toxins
febrifuge - lowers body temperature

relationship to its myth word?  acceptance 

It is said that a tea made from Ash leaves, from budding until midsummer, infuses the body with the vitalizing healing energy of the sun. Some say it is the tree of the goddess Áine, and many say it is the Tree Of Life. Áine, the goddess, is told of in tales that enchant us with thoughts to accept life as it is served to us as then it is golden and warming, but to attempt and control it can only bring coldness and even 'demons' that challenge us.

toxicity? ...  as all plants have a nourishing level and toxic level

Seem like it would take a lot of consumption of Ash plant material to be toxic.
If you have horses, they just love eating Ash leaves and branches, and it is good for them.

Overall, Ash is a useful tree to have around for several reasons.
I encourage you to grow and use Ash trees as much as you can,
especially as they coppice well.

to read about the crafting potential of Ash, please click here