Final answer:
A waste treatment plant would be the most difficult source of pollution to track and regulate.
Step-by-step explanation:
The most difficult source of pollution to track and regulate would be a waste treatment plant. Waste treatment plants are considered point sources of pollution because they release contaminants through a single location, making them more identifiable. However, the challenge lies in the fact that waste treatment plants handle a large volume of wastewater from various sources, making it difficult to trace the exact origins of pollutants and regulate their disposal.