Occurrence Of Chlorinated Paraffins In PVC Products And Its Release During Thermal Process

Persistent Organic Pollutants（POPs）are strictly controlled by countries because of their serious harm to the ecological environment and human health.Among them,short-chain chlorinated Paraffins（SCCPs）have been listed in the Stockholm Convention on Persistent Organic Pollutants due to their strong environmental release potential and POPs characteristics.The content of chlorinated paraffins（CPs）in environmental media in China is at a high level,but its source is still unclear.At present,CPs are mainly used as flame retardants and plasticizers for plastic products such as polyvinyl chloride（PVC）.PVC products may encounter thermochemical processes during the life cycle,and the emission characteristics of CPs in this process are unknown.In this study,the common PVC products in the market of Wuhan were collected,and the PVC products were pretreated by ultrasonic extraction and composite silica gel column purification.The occurrence of CPs in different PVC products were determined by ultra performance liquid chromatography tandem quadrupole-electrostatic field orbitrap high resolution mass spectrometry（UPLC-Q-Orbitrap-MS）.The detection rate of SCCPs and medium chain chlorinated paraffins（MCCPs）in PVC products was100%.The concentration range of∑SCCPs was 1.34×10³-3.90×10⁸ ng/g,and the concentration range of∑MCCPs was 1.29×10³-2.52×10⁸ ng/g.The detection rate of long-chain chlorinated paraffins（LCCPs）was about 91.9%,and the concentration range of∑LCCPs was nd-7.29×10⁶ ng/g.Among the hose products,the concentration distribution range of SCCPs and LCCPs was the widest,and the concentration distribution range of SCCPs was 4.80×10³-3.90×10⁸ ng/g,and the concentration distribution range of LCCPs was 2.00-3.51×10⁶ ng/g.The concentration of MCCPs in wire and cable products was the highest,which was 2.84×10⁶-1.69×10⁸ ng/g.Among all PVC samples,C₁₂,C₁₃,C₁₄ and C₁₈ were the main carbon homologues of SCCPs,MCCPs and LCCPs,respectively.Cl₆ and Cl₇,Cl₈,Cl₉ are the main chlorine-substituted homologues of SCCPs,MCCPs and LCCPs.At the same time,this paper also made a health assessment of the risk of CPs absorbed by PVC products through skin contact,and found that CPs absorbed by PVC products through skin contact did not have obvious hazards and carcinogenic risks.This article selects typical PVC products and uses a vertical tube furnace incineration device to study the release characteristics of CPs during the pyrolysis and incineration process of PVC products under different reaction conditions.The results showed that temperature was the main factor affecting the release of CPs.With the increase of temperature,CPs in PVC products are continuously released into the gas phase,and the concentration of CPs in the gas phase reaches a peak at 400°C.The reaction time also has a certain effect on the release of CPs.Under certain temperature conditions,the longer the reaction time,the more CPs released.The concentration of CPs in the gas phase under anaerobic conditions（4.22×10⁶ ng/g）was higher than that under aerobic conditions（1.14×10⁶ ng/g）,and the concentration of CPs in the gas phase during the slow heating process was higher than that during the rapid heating process,which indicated that the concentration of CPs released into the gas phase was higher under anaerobic conditions and slow heating conditions.Under different conditions,the distribution of carbon homologues did not change significantly.The distribution of chlorine-substituted homologues was mainly Cl₅-Cl₉ homologues,and the temperature had a great influence on the distribution ratio of chlorine-substituted homologues.At400°C,the release amount of SCCPs,MCCPs and LCCPs reached the maximum when the reaction time was 1 h,and the release rates were 3%,0.38%and 40%,respectively.The results of this study show that there are high concentrations of CPs in some PVC products in China,which may release CPs into the environment when they encounter thermal processes such as outdoor incineration and accidental fire.The results of this study help to reveal the sources of CPs in the environment and provide basic data for China’s implementation of the POPs convention and emission reduction work.