| Printed circuit board (PCB) is one of the essential components in all electric and electronic equipments (EEE). As the global PCB production base, China has the largest production amount which is estimated to be214million m. Hundred kinds of chemicals including heavy metals and brominated flame retardants (BFRs), are involved and released during the PCB production, recycling and disposal processes, which may cause severe environmental pollution. However, comprehensive study on contamination and emission of heavy metals and BFRs during the whole life cycle of PCB product is currently limited.In this study, reliable analytical and instrumental methods were built up for the qualitative and quantitative determination of Cu, Zn, Pb, Ni, Cd, Cr, Sn, Polybrominated Diphenyl Ethers (PBDEs) and Tetrabromobisphenol A (TBBPA) in PCB, solid waste and environmental samples. Field investigation and laboratory simulation were both conducted to investigate the contamination and emission of heavy metals and BFRs in three important processes of life cycle of PCB as follows:(1) production,(2) recycling and (3) disposal. Meanwhile, the heavy metals and BFRs released to the environment and the human exposure to those substantces were also evaluated in the above processes.A total of92representative waste printed circuit board (WPCB) samples were randomly collected from large e-waste recycling facilities and small dismantling workshops in China and analyzed for heavy metals and BFRs. The mean concentration exhibited the following order:Cu (189g/kg)> Sn (33.0g/kg)> Pb (17.1g/kg)> Zn (8.91g/kg)> Ni (1.93g/kg)> PBDEs (0.79g/kg)> Cr (0.44g/kg)> Cd (0.26g/kg)> TBBPA (0.17g/kg), with Pb and Cr exceeding the RoHS regulatory limits. The PBDEs profile in our samples of which BDE-47and BDE-99contributed to the majority were quite comparable with the Penta-BDE technical mixture. It suggested that the Penta-BDE techincal mixture used in WPCB, unlike the case of waste plastic, was one of the direct emission sources of lower-BDEs in the environment. Wide variations of the occurrences of heavy metals and BFRs were found in WPCB samples of different source, production place and date, indicating the WPCB from Chinese and Japanese TV sets produced in1995-2000were most highly polluted among all samples. Sorting of those materials is helpful for accomplishing a better control of the potential pollutant release in the subsequent disposal processes. Substance flow analysis was applied to estimate the pollutant inventories in WPCB and the results showed that the increasing tendency of the cumulative inventory of RoHS regulated substance, e.g., Pb, Cr and PBDEs, began to decline after2006, especially for PBDEs (dropping from30-40%to6%). It evidently showed the positive impact of RoHS direction on reducing the application of hazardous substance in EEE.Cu, Zn, Pb, Ni, Cr, Sn and TBBPA were ubiquitous in production wastes collected from a typical PCB plant while Cd and PBDEs were not detected, which was in agreement with the phase-out of hazardous substance in EEE. The low pollutant levels in the effluent showed that limited pollution was released to the environment from well-managed PCB production. The emission factors of pollutants were caculated as follows:Cu> Zn> Sn≈Ni> Pb> Cr>> TBBPA. Emission of heavy metals and BFRs were mainly originated from wet process that consumed rinsing water and dry process that produced solid waste, respectively. Annual emission of Cu to water and land were estimated to be11400and1910kg and those of TBBPA were quite minor (0.02and<0.01kg), which had negligible impact on environment.Heavy metals and BFRs levels in PM10and dust samples from PCB production workshop were relatively higher than those in other related locations ever reported in literatures. Significant correlation among heavy metal in PM10samples suggested similar emission sources. However, insignificant correlation in dust samples indicated that emission sources were more complicated for dust. The distribution of pollutant between dust and PM10were characterised by comparing their concentrations in two phases and the results were given in Log (dust/PM10). The heavy metals pollution occurred mainly in the form of PM10with Log (dust/PM10)<0. Contrarily, TBBPA pollution occurred in the form of dust with Log (dust/PM10)>0. According to the Ward’s clustering method, the distribution pattern was categoried into3types, depending on the production process involved in the workshop.The exposure contribution in workshop presented the following trend:Cu (73.4%)> Sn (10.0%)> Zn (9.38%)> Cr (3.61%)> Pb (2.15%)> Ni (1.09%). TBBPA exposure was quite minor compared to heavy metals but still much higher than the reported value in literature, which indicated that PCB production was an important occupational exposure source of BFRs. Dust ingestion contributed to the majority (69.5%-96.9%) of total exposure pathway. Total Hazardous Index (HI) values of heavy metal exceeded the acceptable level in the milling worshop which suggested potential noncancerous toxic risk to the workers. Carcinogenic risk value of Cr was greater than the threshold value of10"6, suggesting the potential cancerous risk to the worker.Heavy metals and BFRs contamination during WPCB dismantling process was investigated based on a typical WEEE recycling facility. In general, dust and PM10samples from the manual pre-dismantling workshop contained higher levels of heavy metals than those from the mechanical dismantling workshop. Pb was the predominate element in the samples from manual pre-dismantling workshop, whlie the mechanical dismantling workshop was mainly polluted by Cu, resulting from the WPCB dismantling activities. The heavy metals pollution occurred mainly in the form of PM10in the dismantling workshop, which was similar to the PCB production. BDE-209was the predominate congener in the environmental samples collected from WPCB dismantling workshop, which was in disagreement with the congener profile in the WPCB material that was predominated by BDE-47and BDE-99. It was mainly attributed to the vapor/particle partitioning of PBDE congeners in ambient air. In addition, the WPCB dismantling workshop might also be influenced by the dismantling activities of other WEEE, such as plastic that contained high concentration of BDE-209. HI values in both dismantling workshops exceeded the acceptable level, which indicated the potential noncancerous toxic risk to the dismantling workers. Carcinogenic risk value of Ni, Cr and were greater than the threshold value of10-6, which suggested that the workers were exposed to the cancerous risk caused by the dismantling of WPCB.Leaching tests of WPCB using TCLP and SPLP showed the leaching concentration of Cu> Pb> Sn> Zn> Cr> Cd> Ni, with Cu and Pb being the most leachable elements. In the modified NIES leaching tests, initially leacing concentration of BFRs increased sharply, then maintained or even slightly declined after a certain contact period. The leaching behavior fitted well with first-order exponential decay equation and the leaching ratio was influenced by the leachate, the target substance and the specific surface area of WPCB. The potential leached-out volume of BFRs in domestic landfill sites was estimated to reach101kg by the end of2010. These results showed that BFRs had the potential to leach out in short period and became pollution source to soil, landfill leachate and even underground water ocne WPCB were discarded, dumped or disposed in improper ways. |
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