Nitrosamine in the film on leftover oxidized tea?
I don’t think this is a problem. Black tea, for examine, is already oxidized. I don’t think leaving it out would oxidize it much more. Tea has tons of antioxidants that protect against the carcinogenic effects of things like nitrates and oxidization. The biggest source of Nitrosamine in the diet is vegetables, but also not something to worry about because they also contain these protective compounds.
here is some info on the compounds that inhibit carcinogenic Nitrosamine formation
I don’t believe these compounds degrade with heat/light/time particularly since the extract used in the study requires heat to make