Yes, it’s possible with some custom code. It’s a bit complicated because there are several different ways in which the email can be changed, and each one requires a different piece of code to perform the synchronization. I’m not going to go into too much detail, but the way it works is there is an action that is triggered when a user updates their WP user profile, also if they update their Participants Database record, and then the code passes the email address on to the other place it is stored.
So, how this needs to work really depends on the specific interactions that are possible on your site.
From the Participants Database API, there is an action that is triggered when a user updates a Participants Database record: pdb_after_submit_update that action gets the data that was submitted in the update, so your custom code needs to take the email addres from that data and write it to the WP account for the user.
If the user is editing their WP profile, the action that is triggered is personal_options_update and that one gets the WP user ID. You would need to get the newly-saved email value from the account and then write that value to their Participants Database record.
I happen to be working on a plugin that does this kind of thing, it’s a couple of weeks away from release, but if your coding skills aren’t up to setting up this sync, the plugin I’m developing will handle that for you.