Baffled by why my Chicken Soup tasted like Chemicals.

Last Friday, I made a huge Pot of Chicken and Rice Soup. 

I usually just put the pot straight into the fridge.

That's what I did, I put the pot in the fridge 

and

I left a plastic measuring cup in the pot.

                                                                               

HERE IS the Baffling Part!

When I reheated my soup today it tasted like chemicals!

BAHHHHH!

It was horrible!

I gaggingly spit it out and washed my mouth!

• I cant figure out what made it taste like chemicals. 
• The Pot was stainless steel.
• The plastic measuring cup was a bit old.

If you have an idea what may have caused this

Please leave a comment.

Thanks -- Misty