Kodak, of course, is a manufacturer, and as such, they are not neutral about this. I found there are considerable differences in the statements published by the manufacturers, and also in legislation of different countries. Here are some facts:(posted 8606 days ago)Developer is a reducing agent, which means it consumes oxygen dissolved in the waste water. That oxygen, however, is necessary for bacteria to be able to degrade the chemicals.
Many of the compunds in photographic chemistry are also toxic and/or carcinogenic. So in my eyes, it is not at all clear that they are easily degraded in waste-water plants, as manufacturers routinely claim.
Fixer contains silver. Silver has a so-called is a heavy metal and has an oligodynamic effect, which means that in its presence, bacteria will not survive. I have read a Kodak publication on silver in the environment, and they simply state that in the form in which silver is present in used fixing baths, it is not a big problem as most of it is precipitated. As the concentration at which silver kills bacteria is very low, I have my doubts about this statement, too. Also, silver resources are not infinite, and once silver has gone down the drain, it's lost, and we are one step closer to more expensive photo material.
Selenium is a natural TRACE element, and you need a certain amount of it, but it's also highly toxic, and the line between the good effects and the bad ones is extremely thin. I think even Kodak concede that selenium toner shall not be disposed of via the sewer.
So we are actually left to guess. In my country (and I think this applies to most of Europe), it is forbidden anyway to dispose of darkroom chemicals via the sewer. You have to collect them and bring them to a toxic-waste collection point for incineration. (They are available almost everywhere.)
For prints, there is an almost non-toxic developer. That is Agfa's Neutol Plus, where the developing agent is vitamin C. There are probably other less-toxic developers, but photo chemistry remains a pollutant, and if your conscience nags you to act responsibly, I think you won't get around collecting your waste for an ordered disposal.
As for silver: I would try to find someone who's willing to desilver your fixing agents, or use metallic replacement cartidges. (They were an issue from time to time in one of the forums.)