How much API is excreted into water systems?

Dear Network,

I am part of the pharmaceutical pollution hub and I have done some top level work on the area of pharmaceutical pollution. However, I am looking for your help to source where on here I read that 100% of APIs are excreted into our water systems. I am certain I read this and I cannot seem to fin the source if you could kindly help me? 

I know we have said in the past something like between 30-90...but I am sure it is more certain it is higher now...

Thank you in advance of your help.

Kind regards

Mel