What "data issue" are you trying to handle? Are you trying to copy data from the UTF-8 database to the ISO-8859-1 database? Or is your problem something else?
Some of the data that is in the UTF-8 database simply may not be representable in a VARCHAR2 column your ISO-8859-1 database. Assuming that the ISO-8859-1 database has a national character set of UTF-16, you should be able to copy the data from the UTF-8 database into NVARCHAR2 columns in the ISO-8859-1 database.