Mineralization of decachlorobiphenyl in concrete using alcohol washing followed by UV irradiation

Although most of their uses were discontinued by the 1980s, polychlorinated biphenyls (PCBs) persist in building materials, creating a potential hazard and creating a need for cost-effective decontamination methods. To provide a new approach for remediating PCB-contaminated concrete, we employed alcohol washing followed by exposure to ultraviolet (UV) radiation. Extraction of decachlorobiphenyl-contaminated concrete with ethanol or methanol achieved recoveries up to 80%, with lower recoveries observed as the water content of the alcohol increased. Exposure to UV light resulted in transformation of over 99% of the decachlorobiphenyl at a fluence of 840 mJ/cm². The PCB congeners underwent sequential dehalogenation that resulted in complete mineralization of about 30% of the compound at a fluence of 25,200 mJ/cm². Mechanistic studies confirmed that direct UV photolysis was solely responsible for decachlorobiphenyl dehalogenation and mineralization, without a significant contribution from radical-mediated pathways. After UV/alcohol treatment, toxicity testing of the recycled alcohol washing solution showed low developmental toxicity and eliminated the mortality previously associated with decachlorobiphenyl. The estimated cost of treating 1 m³ (i.e., about 2.2 metric tons) of PCB-contaminated concrete is approximately 400 USD. If the alcohol employed in the extraction step is reused, the cost could be reduced by as much as an order of magnitude. These results suggest that alcohol washing followed by UV 254 nm irradiation is a practical and safe approach for remediating PCBs-contaminated concrete.