Hello. Most people don’t put chemicals into the sea on purpose, or sometimes people think they have removed chemicals and later discover that the removal process didn’t work.
Anything that we use that is a chemical in any industry could end up in the ocean or sea as humans might accidently let into the ocean or they might think they can put it down the sick because it won’t harm anyone or thing. Then later we learn that it does cause harm. We are always learning. Hope that answers your question