Halogenated flame retardants (HFRs) are chemicals containing different halogens, including chlorine and bromine, which have been extensively added to a variety of commercial products such as plastics, textiles, electronic appliances and furniture in order to prevent or reduce the spread of fire. Because of their high fireproofing efficiency and low cost, these chemicals have been used in high volumes and consequently, they may leach from the products and be released into the environment. A well-known example is polybrominated diphenyl ethers (PBDEs), which have become chemicals of significant environmental concern due to their similar characteristics to persistent organic pollutants (POPs) including persistence, toxicity, potential for bioaccumulation and long-range transport. Therefore, the technical commercial mixtures, Penta- and Octa-BDEs, have been categorized as POPs and listed under the Stockholm Convention since 2009. Recently, Deca-BDEs have as well been exempted or phased out in the production of electronic applications in European regions and the United States. Accordingly, such situation prompts manufacturers to synthesize and produce non-regulated PBDE alternatives to replace the banned formulations.
Over the past decades, some non-PBDE HFRs, for instance, 1,2-Bis(2,4,6-tribromophenoxy)ethane (BTBPE), Decabromodiphenyl ethane (DBDPE), Dechlorane Plus (DP), Hexabromobenzene (HBB), Hexabromocyclododecanes (HBCDs), Hexachlorocyclopentadienyldibromocyclooctane (HCDBCO), Pentabromoethylbenzene (PBEB), Pentabromotoluene (PBT), 2-Ethylhexyl2,3,4,5-tetrabromobenzoate (TBB), 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) and Bis-(2-ethylhexyl)-tetrabromophthalate (TBPH) have been manufactured to replace PBDEs and these alternatives have been recently investigated and reviewed. The presence of these PBDE alternatives has been reported in a wide range of environmental compartments including biota. The occurrence of these non-PBDE HFRs in organisms of different trophic levels indicates that they can be bioconcentrated and are bioavailable.
In recent years, China has become one of the largest consumers of flame retardants. With the large demand for HFRs in China, coastal ecosystems, especially the estuarine environment, are under severe anthropogenic stress. Discharge from the municipal waters and manufacturing processes could elevate the levels of both PBDEs and alternatives in the environment. The Yangtze River Delta (YRD) is located on the east coast of China and is one of the most vibrant economic regions in China, while the Pearl River Delta (PRD) region has been the leading industrial and economic hub in China as a result of economic reforms started in the early 1980s.
Large-scale industrial development in combination with rapid urbanization may result in high levels of HFRs occurring in these regions. Up till now, little has been known about the presence of PBDE alternatives in the Chinese environment. More investigations are thus urgently needed to provide a better understanding of the distribution and fate of these emerging chemicals in the environment, particularly in the coastal region of China.
In the aquatic environment, sediment acts as a sink and reservoir for POPs. Due to the hydrophobic properties of HFRs, these chemicals tend to accumulate in sediments. Therefore, sediments from both the YRD and PRD were investigated in this study. The results indicated that PBDE, DBDPE and TBECH are the three predominant HFRs with the highest detection frequencies in sediment samples from the YRD. Significant correlation between PBDEs and DBDPE indicates that they may have similar emission sources. The concentration of PBDEs in sediment sample from the PRD is approximately 30 times higher than those in surface sediment samples from the YRD. Different HFR composition patterns were found between these two locations, suggesting that the different HFRs contamination patterns between these two locations may be due to the difference in exposure pathway from the local sources. In general, contamination in the PRD is more severe than that in the YRD region as a result of higher demand for HFRs and the earlier development phase in southern China.
Marine mammals have been regarded as global pollution indicators for POPs because these species are more susceptible to environmental contamination due to their long lifespan, high body lipid content and high trophic level in the marine food web. Two cetacean species, Indo-Pacific humpback dolphin (Sousa chinensis) and finless porpoise (Neophocaena phocaenoides), from the South China Sea, were assessed in this study. Despite the fact that PBDEs were the most dominant brominated flame retardants in the samples analyzed, DBDPE, BTBPE, TBPH, TBB and DP were all detected in both cetacean species. In addition, significant increasing temporal shifting trends of Deca-BDEs to DBDPE, Octa-BDEs to BTBPE, and Deca-BDEs to DP were observed in porpoise samples between 2003 and 2012 and dolphin samples between 2003 and 2011. These patterns may be attributed to the replacement of PBDEs by alternative HFRs and the increasing usage of these alternatives following the restriction/voluntary withdrawal of the production and use of PBDE commercial mixtures. Our findings suggest that the study region may be an important source of contamination by PBDE alternative flame retardants due to the high detection frequencies and levels of these compounds in marine mammals.
In conclusion, the results of this study revealed the current HFR contamination status in the two most developed coastal regions in China. PBDEs and several emerging HFRs such as HBCDs, DBDPE and TBECH are prevalent in the YRD and PRD. Concentration profiles of HFRs in the sediment suggest that some emerging HFRs such as DBDPE will likely become the major HFRs in the coastal environment of China. With regard to the occurrence of HFRs in the cetacean samples, it is the first study documenting the changes of HFR accumulation patterns in blubbers over the past decade. The findings suggest the increasing use of PBDE alternatives in the South China region following the restriction of the production and use of PBDE commercial mixtures. Comprehensive investigation on the exposure pathway, fate and effects of these flame retardants and more toxicological information on these PBDE alternatives are urgently needed.
| Date of Award | 3 Oct 2014 |
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| Original language | English |
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| Awarding Institution | - City University of Hong Kong
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| Supervisor | Kwan Sing Paul LAM (Supervisor) |
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