Upvote:2
Entry requirements can ofter be found on government websites that have travel advice.
The UK government website says for Brazil your passport must have at least 6 months validity.
Your passport should be valid for a minimum period of 6 months from the date of entry into Brazil.
https://www.gov.uk/foreign-travel-advice/brazil/entry-requirements
For Argentina it says just the duration of your stay.
Your passport should be valid for the proposed duration of your stay. No additional period of validity beyond this is required.
https://www.gov.uk/foreign-travel-advice/argentina/entry-requirements
I know this is British travel advice but it will be valid for all passports that have the same visa requirements for these countries. British and Bulgarian citizens have the same entry requirements for both of these countries.