Since photographic processing solutions are deemed (for the most part) biodegradable or harmless, the processing solutions are rather harmless if dumped. Also, the solutions are not all dumped down the drain at once.
As for the sensors, there was a photo of some children and women in an SEA country take as they worked over a landfill looking for precious metals in the debris. It was shown that runoff from rain ran from the landfill to a stream and to a small town. So, the people were getting their doses of Arsenic and Mercury from two sources. This photo was posted on APUG years ago!!!
That is how long this discussion has been going on.