There are several connections between pharmaceuticals and environmental science. The first is that most drugs started as plants -- willow bark contains the chemicals that became aspirin, the heart drug digitalis is made from a shrub, etc. Many drugs are still being discovered in the Amazonian rain forest which is under threat from deforestation and global climate change.
Secondly, many diseases are related to environmental factors and thus pharmaceutical companies in the process of drug development need to take into consideration the ways in which environmental factors affect disease.
Finally, social and physical environment affect drug manufacturing. For example, drugs intended for Africa, due to its hot climate, poor roads, and lack of refrigeration, must be able to withstand high temperatures.