stable , concentrated aqueous suspensions of 2 , 2 - dibromo - 3 - nitrilopropionamide which contribute minimal chemical oxygen demand to systems treated therewith and methods of preparing and using said suspensions in biocidal applications have been discovered . the formulations comprise from about 3 to about 70 weight percent 2 , 2 - dibromo - 3 - nitrilopropionamide suspended in about 30 to about 97 weight percent water in the presence of a suspending amount of a thixotrope that exhibits ellis - plastic behavior , such as xantham gum and locust bean gum , at a ph of from about 1 to about 4 .