Join and order polymorphic relationships in Laravel

I have a problem. Let's say, I have a table of

personal_contacts[name, email, something_else]

and table of

organisation_contacts[title, email, something, smth_else].

Both tables contains email column.

Besides, I have a table of

needed_contacts[belonging_id, belonging_type],

that is in polymorphic relation to other two.

Now, I need to order needed_contacts by relationship's email field. I was planning to do this with joins and than order by email field, but I get an error, if I don't rename one field:

Integrity constraint violation: Column 'email' in field list is ambiguous

Is it even possible to achieve, what I am trying to do? Any help, pointers or comments would be appreciated.

My php code is:

NeededContact::leftJoin('personal_contacts', function($join){
   $join->on('personal_contacts.id', '=', 'needed_contacts.belonging_id')->where('needed_contacts.belonging_type', '=', 'PersonalContact');
})
->leftJoin('organisation_contacts', function($join){
   $join->on('organisation_contacts.id', '=', 'needed_contacts.belonging_id')->where('needed_contacts.belonging_type', '=', 'OrganisationContact');
})
->orderBy('email', 'desc');

via Chebli Mohamed