Note: Garbage Collection environment variables for SGen (MONO_GC_PARAMS) set this way will only be used when launching from Xamarin Studio. If you launch the app from the device, Xamarin requires certain settings so the settings for Sgen will be ignored.
To permanently set an environment variable for an app, you need to add this as an additional mtouch argument (for all relevant configurations):
To see the environment variables that can be set, refer to the Mono man page:
See the section titled "ENVIRONMENT VARIABLES"