Additional troubleshooting queries:

http://troubleshootingsql.com/2010/02/16/how-to-find-who-is-usingeating-up-the-virtual-address-space-on-your-sql-server/

If the above doesn't help, then a more invasive way to identify the culprit would be to capture XPerf traces: http://troubleshootingsql.com/2011/05/31/tools-tips-and-tricks-12-xperf-memory-usage-and-much-more/

Or capture a Debug Diag memory leak trace:

http://troubleshootingsql.com/2011/05/27/tools-tips-and-tricks-11-debug-diag-and-memory-leaks/