The bond in water is the relatively weak hydrogen bond, the atom is so small it has problems hanging on to things. The bond angle is created by the repulsive/attactive forces between the hydrogen atoms. I dont see how pollution can change this angle. However O16/18 have different atomic weight ratios so I would assume that changes the repulsion/attraction force and thus the angle. Maybe someone in chemistry can quantify this relationship, I am a mere Geophysicist.
Now when ice forms it would rather take in O16 I believe, so the concentration of O18 in the environment increases during say Ice Ages.
I would like to see more info on this theory. Every compound is impure, water carries calcium, sulfur, carbon etc. but the environment filters this out through the water cycle. I have no doubt contaminates in the water are increasing, but I dont know if bond angle plays into this.

