As human beings take more medications, so the environment becomes saturated with drugs. Sewerage treatment works are having a difficult problem removing them and providing usable water.
Even low levels of these dangerous chemicals can damage fish, for example. When exposed to anti-stress drugs they get hungry like drug addicts and eat until they are blotted.
Very small microbes that keep the environment running effectively no longer do their work on slime to create food for fish. Chemicals such as shampoo, washing powder, disinfectants, caffeine, antihistamines and antibiotics upset the ecosystem. They slow production of algae a base food source.
Basically, waterways are being sterilized. It is difficult to ascertain the impact of each drug because there are a number of pollutants present at any one time. Pesticides and fertilizers are mixed in with drugs.