Aggie, I agree with you completely about the fear of chemicals and thank you for the nice comment. I have worked with chemicals most of my life, starting in photography at about 12 and being rather senior right now. I'm still here and so far only natural processes appear to have aged me.
Ole and Jim are right as well. Some of the worst chemical preparations are those containing mercury and lead as well as pyro. My experience and the data at EK indicated how bad they are. Organic solvents are murder on the kidneys but you need massive exposure to begin to have problems.
The public fears the unknown and to them chemistry is a 'black hole' that is deep dark and mysterious. It scares them and people make a living feeding on those fears.
I've been using Cadmium lately in my tests. I have no results to report so far. They are ambiguous. I would guess that it would have to be placed directly in the emulsion when you make it to have any useful effect. In the case of Cd, you have to be careful of the dust or of getting the chemical into an open wound. Don't eat it or drink anything containing cadmium. Gee, that kinda makes sense to me. Otherwise it is rather harmless.
If you poured Cadmium Chloride and Copper Chloride on your lawn, the Cd is considered a No-No, but the copper is considered benign. However, at moderate concentrations, the Cd has no effect but the Cu acts as an herbicide and will kill grass, shrubs and trees. So, don't backwash your pool onto your lawn. The algaecides in the water (copper and others), if any, can kill your plants. Then again, Copper salts are found in Miracid which is an excellent plant fertilzer. Go figure!
So, you see it depends on chemical, concentration and sometimes oxidation state before you can call a chemical toxic.
Here is another for you. If you read up on EDTA it will scare you silly being a 'toxic chemical', but it is used intravenously in cases of heavy metal poisoning. How can it be a toxic chemcial and still be injected intravenously puzzles me.
Well, enough rambling. I do believe in a clean environment, having lived in Japan for a while. I saw how their industry 'worked' and how bad the air and water quality was. I see how other countries don't seem to care and are able to sell cheaper products by ignoring the consequences of pollution. I see our environment improving and I hope we can strike a safe balance with good education that will allow us to practice photography in the way we have become accustomed without paying a heavy penalty for using chemicals.
PE