Oxidative Transformation of Controlled Substances by Manganese Dioxide

This study investigated the oxidative transformation of four controlled substances (ketamine, methamphetamine, morphine, and codeine) by synthesized MnO(2) (δ-MnO(2)) in aqueous environments. The results indicated that ketamine and methamphetamine were negligibly oxidized by MnO(2) and, thus, may be persistent in the aqueous environment. However, morphine and codeine were able to be oxidized by MnO(2), which indicated that they are likely naturally attenuated in aqueous environments. Overall, lower solution pH values, lower initial compound concentrations, and higher MnO(2) loading resulted in a faster reaction rate. The oxidation of morphine was inhibited in the presence of metal ions (Mn(2+), Fe(3+), Ca(2+), and Mg(2+)) and fulvic acid. However, the addition of Fe(3+) and fulvic acid enhanced codeine oxidation. A second-order kinetics model described the oxidation of morphine and codeine by MnO(2); it suggested that the formation of a surface precursor complex between the target compound and the MnO(2) surface was the rate-limiting step. Although the target compounds were degraded, the slow TOC removal indicated that several byproducts were formed and persist against further MnO(2) oxidation.