Why are ecologists unsettled on whether or not any truly commensal interactions among organisms?

Ecologists are unsettled on whether or not any truly commensal interactions among organisms take place or not because it depends on the kind of organisms. When a bird makes a nest in a tree and lays eggs, the eggs are definitely safe. This procedure does not harm the tree directly, but it can stop the sunlight from reaching some parts of the tree. This actually shows that the bird has benefited from the situation but the tree has lost out. 

The answer to this question is  c. pharmaceutical accumulation  reclaimed water refers to the water that being used again after it already  used for agricultural purposes.this type of water often contains pharmaceutical accumulation because of the chemical fertilizer that is used for the plants is absorbed into the water.