ISO 20121 Event Sustainability Management System is an International Standard that was published in 2012.
The standard contains requirements for an event sustainability management system. It is possible to voluntarily demonstrate conformity by using first party (self-determination and self-declaration), second party (confirmation of conformance by parties having an interest in the organization, such as clients, or by other persons on their behalf), or an independent third party (e.g. a certification body).
ISO 20121 contains several references to ISO 26000.
More information is available at http://www.iso20121.org/ .