both of them should be safe. From my basic level of chemistry, (C at AS level... so i suck)
K2SO4 (potassium sulphate) Is stable in its dry form. I believe when it contacts water, it might fizz a bit. I would advise you minimise the contact between your skin and the stuff though. There should be no normal potassium present in the mix as straight potassium will burn in normal oxygen
Me and my mates used to "liberate" all the science stuff to do all the experiments my teacher didnt want us to do and once this clown took some potassium and covered it in oil, then put it in a tissue and left it in his blazer. Then it started raining and his jacket gotburned through lol!
Potassium phosphate i believe is acidic so avoid contact with your hands, especially if they are wet. If you do touch it, pour anything alkali such as milk i think to counter it. Do not rinse under water, you will just feed the burning.
Chemistry lesson 1: Substances are only acid or alkali in liquid form (i think its when mixed with water speciffically) Even with dry hands, you still release sweat which acts as water and can cause a reaction with solid substances to become acid or alkali. So dont touch it
I think when acids are in their pure form as acids, they are non-reactive and theoretically, if you were to not have any water on your arms, you could put it straight in the water and not be affected at all.
no idea about the trace elements.