The Disinfectant Residues Promote The Aging Process Of Plastic Water Pipes And Its Potential Hazard

In recent years,as people’s requirements for the quality of drinking water are getting higher and higher,metal water supply pipes that are prone to rust and pollute water quality has been gradually replaced by plastic pipes.The phenomenon of plastic aging due to various conditions in the environment has become a new pollution problem.The residual disinfectant in the water supply pipe network is oxidizing,which is bound to oxidize plastic pipes,affect the aging process of plastic pipes,and then affect the quality of drinking water and threaten human health.Therefore,it is of great significance to explore the aging effect of residual disinfectants on plastic pipes and the potential hazard of aging products.In this study,four disinfectants,chlorine dioxide,sodium hypochlorite,trichloroisocyanuric acid（TCCA）,and ozone were selected to carry out aging experiments on unplasticized polyvinyl chloride（u PVC）and Polypropylene-Random（PPR）pipes which are widely used in the market.The changes of surface morphology,functional groups,hydrophobicity,and crystallinity of plastic pipes under the action of disinfectants were analyzed.The organic matter in the solution was quantified,the fluorescence characteristics of the plastic leaching solution were analyzed,and the types of aging products were identified.The potential hazard of aging products was evaluated by mouse colon cancer cells.Finally,the occurrence of microplastics in local tap water was investigated.The results showed that after 75 days of disinfectant,pores,cracks and oxygen-containing functional groups appeared on the surface of plastic pipes.The crystallinity of some plastics increases and the hydrophilicity changes,which proves that the plastic pipes are aging.According to 2D-COS analysis,the polymer chains of u PVC plastics fractured in the order of-CH₂-CHCl-→-CH-Cl-→C-Cl and the order of PPR structure change was-CH₂ bending→aromatic C=C double bond→CH₃ symmetric deformation→C-C stretching.Superoxide radicals,hydroxyl radicals,and chlorine radicals were the main types of reactive species in the reaction system,and the mechanism of plastic aging was described.The amount of organic matter released from the plastic pipes increased with the increase of aging time,and the effect was chlorine dioxide>ozone>trichloroisocyanuric acid>sodium hypochlorite.The amount of organic matter released from PPR was higher than that of u PVC.The position and intensity of the three-dimensional fluorescence peak of the plastic leaching solution were constantly changing,and the organic matter was constantly reacting with the disinfectants to form secondary products.Plastic additives such as plasticizers,antioxidants,stabilizers,and polymer degradation products were identified in the released leaching solution.Cytotoxicity experiments showed that plastic aging products inhibited cell proliferation and induced oxidative stress in cells in a dose-dependent manner.The concentration of microplastics in Kunming tap water was 282-315 n/L,and the pollution level was relatively high.The shapes include fibers,particles,and debris.Microplastic types include high-density polyethylene,low-density polyethylene,polyvinyl chloride,polycarbonate,and polypropylene.This study shows that disinfectants can accelerate the aging of plastic pipes and change the physical and chemical properties of plastic pipes.Plastic pipes will release additives and other aging products into the environment after aging,which has toxic effects on cells.At the same time,the organic matter released by the plastic pipes may react with the residual disinfectants twice to produce substances with potential hazard.Plastic pipes aging is an important source of microplastics in tap water.This provides important reference value and practical significance for the pollution prevention and control of microplastics and plastic aging products in drinking water.