Pharmaceutical drugs given to people and to domestic animals - including antibiotics, hormones, strong pain killers, tranquilisers and chemotherapy chemicals - find their way into the food chain, the soil and water. No drug has ever been refused entry into the market based on estimated environmental concentrations and no actual testing is conducted after a drug is marketed to see if the environmental concentration was estimated correctly. Controls on drugs have been the brief of health departments, which are concerned only with the effect of drugs on the humans to which they are administered.
Large quantities of drugs are excreted by humans and domestic animals, and are distributed into the environment by flushing toilets and by spreading manure and sewage sludge onto and into soil. Some drugs reach the environment in their original form, and sometimes as by-products broken down by the human body. Some of the metabolites are more reactive and sometimes more toxic than the parent drug. Pharmaceuticals can be present in the environment at concentrations similar to those of pesticides, and like them they can be highly mobile and persistent.
Drug residues seep from a marine waste dump of the north coast of Puerto Rico, where millions of litres of pharamaceutical waste were tipped into the sea annually between 1972 and 1983.