Boron-doped diamond activation of peroxymonosulfate for the safe and complete mineralization of the anticancer drug dacarbazine: role of the oxidant in controlling toxic by-products

Anticancer drugs are emerging contaminants of increasing concern, as their mutagenic and cytotoxic character poses a risk to aquatic ecosystems, and their treatment must ensure not only removal of the parent compound but also the avoidance of equally hazardous transformation by-products. Yet the electrochemical degradation of dacarbazine (DTIC), a widely administered anticancer drug, has not been previously investigated. This study evaluated the electrochemical activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) using a boron-doped diamond (BDD) anode to degrade DTIC in water, benchmarked against the electrolysis of SO 4 2- and Cl - at current densities of 5, 10, and 50 mA cm -2 . The Cl - system achieved the fastest DTIC removal and the lowest energy consumption, driven by Cl • radicals, but the progressive conversion of reactive chlorine into chlorate and perchlorate limited mineralization and generated persistent chlorinated by-products. PMS and PDS enhanced SO 4 •- production relative to SO 4 2- alone, as confirmed by quenching experiments, improving both removal and mineralization. Complete DTIC mineralization was achieved exclusively with PMS at 50 mA cm -2 , supported by the full disappearance of all transformation products and carboxylates detected by LC-MS and IC. In contrast, the SO 4 2- and PDS systems accumulated a persistent intermediate predicted to be more toxic than the parent compound. These results establish BDD-mediated PMS activation as the most effective and environmentally sound strategy for DTIC treatment in water, uniquely capable of achieving complete mineralization while avoiding the toxic chlorinated and persistent by-products generated by the other systems.