Aquatic toxicity and solution stability of two organic corrosion inhibitors: 2-mercaptobenzothiazole and 1,2,3-benzotriazole

Proprietary corrosion inhibitors often contain organic compounds that are s orbed onto bronze metal surfaces. Since the inhibitors are added to the pap ermaking system, progressive water closure implies that they could accumula te in effluents to high concentrations. It is important to determine aquati c toxicities of active ingredients of the inhibitors, and to investigate th eir solution stabilities. Using 96 hour acute lethality bioassays on rainbo w trout, we observed the 96 h LC50 values of 2-mercaptobenzothiazole (2-MBT ) to be 1.3 and 6.2 mg/L at pH 6.5 and pH 8, respectively. As expected, the undissociated form of the compound is more toxic than the dissociated one. The 96 h LC50 value of 1,2,3-benzotriazole was 35 mg/L at pH 8. This compo und is a weaker acid (pK(a)>8) than 2-MBT (pK(a)=6.9); in neutral and weakl y alkaline solutions it is mostly in the undissociated form. Its observed t oxicity was lower than that of 2-MBT. Data from monitoring the air-saturate d aqueous solutions of individual compounds by liquid chromatography show t hat the inhibitors are stable in solution.