Just a wild guess... but maybe you could try binding the parameters explicitly using bind_param, which would allow you to specify the type in \%attr, such as { ora_type => ORA_BLOB }  (for this, you'll also have to import the type constants: use DBD::Oracle qw{:ora_types};).

When you simply pass a list of parameters to execute, the driver does some guessing to determine the type for the binding that's done behind the scenes, but this often goes wrong for anything but simple types.

See also Placeholder Binding Attributes.