These terms relate to the nature of emissions or their consequences. This is a pollutant that accumulates in the environment once released. A good example is lead or mercury. Since the environment's assimilative capacity is essentially non-existant, they tend to accumulate in the environment.
Acid rain can cause leaching of important nutrients from the soil.
By contrast, landfills have a leaching problem because rain may cause contaminants to be leached into the water table. By contrast, non-point source emissions are spread more evenly across a wider area. The fertilizer or pesticide runoff from grain farms is a non-point source emission.