Film photography embraces the use of chemicals. For the most part, the chemicals we use are benign; otherwise the darkrooms of the world would be labeled as a hazardous workplace. Not to say there is absolutely no danger as the potential to mishandle chemicals is with us always.
There are a plethora of developer formulas, all have advantages and disadvantages. However, all developers are similar as to their potential hazards. The black & white developer, Rodinal included, consists of 5 chief ingredients.
Water solvent: All the chemicals of construction are dissolved in water and water is the chief ingredient.
Developing agent: A developer likely has two or more. These are organic chemicals able to reduce (liberate) metals from their salts. They have an affinity for oxygen. All are kinsfolks of benzene initially fashioned from coal. Spent developing agents revert to coal tar.
Accelerator: The developing agents work in an alkaline environment. The more aggressive developers contain strong bases. Rodinal sets the pH alkaline using potassium hydroxide.
Preservative: Sodium sulfite, reduces the potential for oxidation and neutralizes the staining agents that form from oxidized developing agents.
Restrainer: Forces the developer to become selective. Without a restrainer the dev eloper will over-develop and thus fog the film. This chemical is potassium bromide.
Is this a particularly hazardous solution? Answer is no but – skin reactions with rash are not uncommon. Don’t drink or bath in this formula. Wash all vessels and utensils – use of rubber gloves advised.