LIMA, May 25 (Reuters) - Peru´s sol currency plunged to an historic low on Tuesday as recent polls showed presidential front-runner and socialist Pedro Castillo with a growing lead over business-friendly conservative Keiko Fujimori. The sol fell 0.87% to 3.840/3.845 per dollar. (Reporting by Marco Aquino, writing by Dave Sherwood, editing by Chris Reese) Our Standards: The Thomson Reuters Trust Principles.