Lead can be used to form a low speed anti-wear film. It used to be used in slow speed gear lubes that had high loads but low speeds. NEO use's it in their oil and gear lubes. It is one of the things I hate about their oil is that it makes getting a good read on bearing wear almost impossable it is like when you use leaded fuel like in aviation.... It just add's to the issue of interpreting the UOA.
I do not know about the arsenic or cadmium but many heavy metals can be made to work as anti-wear agents tungsten has been tried and antimony and Conoco Phillips is advertising a titanium derived anti-wear agent so it is a possibility! We need to have Molakule chime in with this information!