The transformation and interaction of diallyl phthalate (DAP) in the three kinds of plastic under ultraviolet/sodium dichloroisocyanurate (UV/DCCNa) disinfection process

Abstract

In this work, the degradation kinetics and transformation pathways of diallyl phthalate (DAP) in polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) plastics under UV/sodium dichloroisocyanurate (UV/DCCNa) disinfection process were studied comparatively. The results showed that the degradation efficiency of DAP in PE plastics was highest compared with PP and PVC plastics, and it was not affected by hypochlorous acid (HOCl) concentration. These phenomena were attributed to the different reaction activation energy (Ea) between plastics and active free radicals (OH, Cl, and ClO) and the difference in the contribution of Cl under the action of UV illumination. Moreover, some ions such as NH4+, Cl−, NO3−, SO42−, and HCO3− could significantly affect the degradation of DAP. Then, we detected a total of fifty-four kinds of interactive products between DAP and plastics and proposed the transformation pathways including hydroxylation, chlorination, hydrolysis, nitrosation, bond breaking, coupling, and interactive reaction after intermediate products were identified. The UV/chlorination process was also performed under low-temperature conditions, and it was found that the degradation of DAP was not inhibited even at 0 °C, with yields of disinfection byproduct in PP plastics being the highest. Further, the results of the toxicity assessment for products indicated that sixty-six of the intermediates were developmental toxicants and nine of them were mutagenicity positive with a higher possibility than DAP, which means there are still some environmental health risks after the UV/DCCNa disinfection process for plastics. This study provided insights into the interaction and health risk management between DAP and plastics during the cold chain disinfection process.