THE HYDROLYSIS OF DIISOPROPYL METHYLPHOSPHONATE IN-GROUND WATER

The half-life of di-isopropyl methylphosphonate (DIMP) in ground water at 10 degrees C was estimated to be 500 years with a 95% confidence i nterval of 447 to 559 years from measurements of the hydrolysis rates at four temperatures ranging between 70 and 98 degrees C. First-order kinetics were assumed, and the Arrhenius equation was used to extrapol ate the hydrolysis rates to the normal temperature of ground water, 10 degrees C. The half-life calculated at this temperature for ASTM Type II water was estimated to be 684 years with a 95% confidence interval of 470 to 995 years, in agreement with a previously published study. The major hydrolysis products detected were isopropyl methylphosphonic acid and methylphosphonic acid. After heating samples for 43 days at 90 degrees C, the molar accounting of the remaining DIMP and its detec ted hydrolysis products was 15% of the starting material. Inorganic ph osphate was not detected. The very slow rate of DIMP hydrolysis in gro und water suggests that the unidentified products are not likely to ac cumulate to any significant extent.