AFAIK, it's not.  You'll have to write a separate program to periodically check the database and send out the email when the field value changes.  Some things to think about - How do you know that it's changed?  Are you keeping some sort of change history for the table?  You need to be able to compare the current value with the value in the most recent change record to determine whether it's changed and you need to track when the program last emailed out anything to determine whether the change was made since the last time the process was run.

Consider a 3rd-party tool as a solution (for a list of such tools, see http://www.kenhamady.com/bookmarks.html).

My Visual CUT software provides this type of functionality.  Avoiding duplicate emails can be done using the optional Skip_Recent command line argument (see detail in the user manual) or by turning on the option to log processing to an ODBC table (and including that table within the report).

- Ido