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Are you talking about sodium thiosulfate? It's less acutely toxic (oral LD 50) than table salt in animals, has no known chronic health risks, doesn't persist in

Are you talking about sodium thiosulfate? It's less acutely toxic (oral LD 50) than table salt in animals, has no known chronic health risks, doesn't persist in the environment, and is non-flammable.

parshimers 6y ago
Yes, but once it becomes laden with powdered, precipitated silver it is far less benign. Silver is still a heavy metal after all, even if it is not the most acutely dangerous one.
- foobar1962 6y ago
  The problem then is the dissolved silver, not the thiosulphate.
  - namibj 6y ago
    And just evaporating it down should be a suitable concentration step, if not just electroplating the silver out of solution with a graphite anode or something like that.
jimv206 6y ago
This is true with regards to fresh fixer but, once it's used it contains silver which, as reported by, sciencedaily.com: "We found that silver nanoparticles are extremely toxic. The nanoparticles destroy the benign species of bacteria that are used for wastewater treatment. It basically halts the reproduction activity of the good bacteria." I photograph onto paper, develop with caffenol, digitize after the stop bath (quickly) and discard the paper so as to avoid using fixer. Yes, there is silver on that paper but I'm hoping that silver in an incinerator or even landfill is better than silver in the wastewater. Back in the day when analog photography was just called photography, there were inexpensive silver recovery filters available. Now, if you want to use fixer, try to find a local film lab that will take your "spent" fixer.
- fao_ 6y ago
  Well, no. It's illegal (in any coherent district) to put hard chemical waste (like silver) into the wastewater. you either take it to, as you suggested, a local film lab, or you clearly label it, build up several gallons of it, and take it to a chemical treatment factory, or whatever distribution process you have to get it there. Like NileRed does.

Are you talking about sodium thiosulfate? It's less acutely toxic (oral LD 50) than table salt in animals, has no known chronic health risks, doesn't persist in the environment, and is non-flammable.

parshimers 6y ago

Yes, but once it becomes laden with powdered, precipitated silver it is far less benign. Silver is still a heavy metal after all, even if it is not the most acutely dangerous one.

foobar1962 6y ago
The problem then is the dissolved silver, not the thiosulphate.
- namibj 6y ago
  And just evaporating it down should be a suitable concentration step, if not just electroplating the silver out of solution with a graphite anode or something like that.

jimv206 6y ago

This is true with regards to fresh fixer but, once it's used it contains silver which, as reported by, sciencedaily.com: "We found that silver nanoparticles are extremely toxic. The nanoparticles destroy the benign species of bacteria that are used for wastewater treatment. It basically halts the reproduction activity of the good bacteria." I photograph onto paper, develop with caffenol, digitize after the stop bath (quickly) and discard the paper so as to avoid using fixer. Yes, there is silver on that paper but I'm hoping that silver in an incinerator or even landfill is better than silver in the wastewater. Back in the day when analog photography was just called photography, there were inexpensive silver recovery filters available. Now, if you want to use fixer, try to find a local film lab that will take your "spent" fixer.

fao_ 6y ago
Well, no. It's illegal (in any coherent district) to put hard chemical waste (like silver) into the wastewater. you either take it to, as you suggested, a local film lab, or you clearly label it, build up several gallons of it, and take it to a chemical treatment factory, or whatever distribution process you have to get it there. Like NileRed does.