Final answer:
The environmental concern described is leaching, where nutrients needed for medicine production are washed away by deforestation.
Step-by-step explanation:
The environmental concern in the scenario where Diane, who has diabetes and relies on medicine, is worried about the loss of nutrients due to deforestation relates to the concept of leaching. Deforestation can cause soil erosion and the removal of nutrients, which might be used in the production of medicines, through water runoff. Since the scenario specifically mentions the washing away of nutrients as a result of deforestation, the most accurate option from the provided choices would be 'b) Leaching'.