How can the use of ammonium nitrate by terrorists be pre- vented? The most logical approach is to desensitize or neutral- ize the compound's ability to act as an explosive. but to date no satisfactory way has been found to do so without diminishing its value as a fertilizer. A more passive method is to add to the fertilizer an agent known as a taggant, which would allow law enforcement to trace the source of an ammonium nitrate explo- sive. A number of European countries now forbid the sale of ammonium nitrate without taggants, although the U.S. Congress has yet to pass such a law