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The study has investigated the annual variation of the dry and wet depositions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) among different kinds of areas. A commercial suburban area, an industrial urban area, a coastal rural area and an agricultural rural area were chosen to measure the PCDD/F depositions in each season. The mean TEQ concentration, dry deposition flux and wet deposition in the industrial urban area all had the highest values, at 0.0958 pg I-TEQ/Nm 3 , 29.1 pg I-TEQ/m 2 -d and 47.8 pg/L, respectively. Additionally, the annual total deposition flux of PCDD/Fs in the commercial, industrial, coastal and agricultural areas was 168, 310, 135 and 115 ng/m 2 -year, respectively. The seasonal change of PCDD/Fs in air could be affected by heating and temperature inversion in winter or photodegradation and OH radical reaction in summer. The various homologue profiles of PCDD/Fs probably affect the distribution in environmental sinks, such as sediments or the living organisms in rivers or seas. Additionally, the results of statistical analysis indicated that PCDD I-TEQ dry deposition flux (ng I-TEQ/m 2 -month) was negatively correlated with the ambient temperature (r = -0.843) for the agricultural rural area, possibly due to vapor pressure (temperature-dependent) effect on the gas/particle PCDD/F partitioning. Furthermore, the PCDD/F concentration of wet deposition flux (ng I-TEQ/m 2 -month) was positively correlated with the monthly rainfall (r = 0.826-0.988) at the four sampling areas.

Waste printed circuit boards containing brominated flame retardants were pyrolyzed in a high-temperature melting system to observe the formation behaviors of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). In this study, the results showed that the formation of PBDD/ Fs during pyrolysis can be destroyed under controlled primary combustion conditions. There were two significant factors that influenced the extent of PBDD/F formation. The first factor was temperature. The results showed that, both the total PBDD/F content in the bottom ash and the total PBDD/F emission factor from the flue gas decrease by approximately 50% with an increase of the pyrolysis temperature from 850 to 1200 degrees C. The second factor was the addition of CaO. The possible mechanism involves the reaction between CaO and HBr to form the solid-phase product CaBr2. Thus, the addition of CaO is effective in adsorbing HBr and results in the inhibition of PBDD/F synthesis by more than 90% and further prevents the acid gases (HCl and HBr) that corrode the equipment. In conclusion, due to the persistence and toxicity of PBDD/Fs, a combined regulation for controlling both PCDD/Fs and PBDD/Fs is of great importance for environmental protection issues.

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