Sodium sulfite is toxic to rats. The LD50 is less than 5000 mg/kg which would make it toxicity category D and a dangerous waste in Washington state in amounts of 10% or greater. MSDS for sodium sulfite

I'd like to find out if there are any fish bioassay results on rainbow trout. Sodium sulfite was a common ingredient in photo developer. I haven't done waste designation for quite some time. I'll see if I can dig up a list I have of fish bioassay data. I know the test used to cost around $800 and we used to contract that testing with Sound Analytical.