A simplified approach using the competition kinetics method allows the estimation of
reaction efficiencies when one specific radical species is dominant, but it does not allow
estimation of overall kinetic rates. Since the concentration of the radical is the same for all
reactions involving it, competition kinetics predicts that the relative dominance of each
particular reaction within a system depends on the product of each reactant’s concentration
with its second-order reaction rate. Those reactants with either faster rates of reaction or higher
concentrations tend to dominate. Peyton (1993) demonstrated that this method could be useful
for analyzing the persulfate chemistry of TOC analyzers. It may also have some utility for
ISCO as well. However, there are a number of unknowns with ISCO that make conclusions with
this method more uncertain. For example, the reactivity of persulfate with soil minerals is
largely unknown, but with hydrogen peroxide, soil minerals have a major effect on free radical
reactions, and failing to include them in competition kinetic calculations could impart significant
error. Furthermore, when there are multiple radical species contributing to degradation,
competition kinetics cannot easily account for the impact of other radicals.
Because of the multiple and perhaps unclear reaction pathways occurring during persulfate
degradation of organic contaminants, modeling persulfate oxidation kinetics at this point in
time is plagued by a high degree of uncertainty. Hence, the most common approach for
investigating reaction kinetics is to collect relevant laboratory data and then extrapolate these
findings to in situ conditions. In many cases, pseudo first-order kinetics appear to hold for