Comment by z2

I think this is the right approach, speaking as someone who went down the rabbit-hole of looking at alternative non-bisphenol or non-phenol image developers. The very little research on the new ones tend to conclude "we don't know if it's toxic in the long term" or in the case of urea-based papers, "it's highly toxic against aquatic life."

To the GP, if the goal is to avoid phenol papers, phenol papers tend to develop deeper black. And in the US, phenol-free papers are new enough the backside often advertises it. Some are very misleadingly labeled BPA-free, which usually means it's made with the very similar and likely equally toxic BPS.