dropping a user in 8.2.6

I am using version 8.2.6

I created a role and granted all on table "instrument" in the database.  But, when I tried to drop the role, I get the following error:

mydb=# drop role system_dba;
ERROR:  role "user1" cannot be dropped because some objects depend on it
DETAIL:  access to table mydb_admin.instrument

Is there a way to drop a role with some sort of "cascade" option?