Silver, and 5.0 mg/L
Updated
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The characteristic
A solid waste exhibits the characteristic of toxicity if, using the Toxicity Characteristic Leaching Procedure, the extract from a representative sample contains a Table 1 contaminant at or above the listed concentration.
The row that matters
EPA hazardous waste number D011, contaminant Silver, CAS number 7440-22-4, regulatory level 5.0 mg/L. That is the whole of the silver provision and it is a single line in a long table.
And the sentence that simplifies it
Where the waste contains less than 0.5 percent filterable solids, the waste itself, after filtering using the methodology in Method 1311, is considered to be the extract for the purpose of the section.
Which is what spent fixer is
A liquid with essentially no filterable solids. So there is no leaching procedure to run and no extract to prepare: the silver concentration in the fixer is the number compared against 5.0 mg/L.
And ordinary use clears it comfortably
Fixer works by dissolving silver halides out of the emulsion, so silver accumulates in it by design. A working fixer that has done its job is usually far above 5 mg/L, which is why this is treated as the normal case rather than the exception.
Developer and stop bath are different questions
They do not accumulate silver the way fixer does, so the silver characteristic is not the issue for them. They may raise other questions, including pH, and they get their own determination rather than being assumed in or out.
The characteristic attaches to the waste, not to the product
A fresh bottle of fixer is a product with a hazard communication or consumer label. The same chemistry after use is a waste with a determination. Two regimes, and the standard expressly excludes RCRA waste from hazard communication.