Duo xiu lian ben mi, gong mian duo lü lian ben, duo lü lian ben er e ying ji duo lü lian ben fu nan dui sheng huo zai xiang gang shui yu de jing tun de feng xian ping gu | 多溴聯苯醚, 共面多氯聯苯, 多氯聯苯二噁英及多氯聯苯夫喃對生活在香港水域的鯨豚的風險評估 | Risk assessment of polybrominated diphenyl ethers, coplanar polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in cetaceans in Hong Kong waters

Includes bibliographical references (leaves 106-129)

Sixteen species of marine mammals have been identified in Hong Kong waters. However, only the Indo-Pacific humpback dolphin (Sousa chinensis) and the finless porpoise (Neophocaena phocaenoides) are local residents. There is increasing evidence that these two top predators may be under severe environmental pressure, particularly from environmental pollution. The marine environment of Hong Kong receives vast quantities of toxic contaminants from local sewage and industrial effluent, as well as discharge from the Pearl River Delta region. Since industrial and urban development is increasing in this region, marine mammals inhabiting Hong Kong waters may accumulate contaminants through the food chain that potentially threaten their health. Previous studies have demonstrated that humpback dolphins and finless porpoises in Hong Kong have accumulated a range of contaminants, including trace elements, polycyclic aromatic hydrocarbons, polychlorinated biphenyls (PCBs) and organochlorine pesticides, at concentrations that may be vulnerable to toxic effects. Dioxins and related compounds, including non- and mono-ortho PCBs, polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), are of particular concern since they have been shown to be highly toxic in animal studies. Brominated flame retardants, particularly polybrominated diphenyl ethers (PBDEs), are also of concern since their levels have been increasing in the environment and biota in the past 30 years, and some epidemiological studies have also indicated that bioaccumulation of these persistent toxic substances may cause adverse biological effects in mammals. This study performed a post-mortem investigation of the contamination status of PBDEs, coplanar PCBs, PCDDs and PCDFs in stranded cetaceans from Hong Kong waters. It also assessed the potential risks of adverse health effects that these compounds pose in these cetaceans. Blubber tissues of the Indo-Pacific humpback dolphins and finless porpoises were collected and the levels of the stated contaminants were examined. Analysis of PBDEs involved extraction, lipid determination, purification and fractionation by chromatography on a silica gel column, and gas chromatography using a mass-selective detector operating in electron impact mode for quantification and confirmation of component identities. The determination of coplanar PCBs and PCDDs/DFs was performed by the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. The mean concentrations of total PBDEs (summation of 14 PBDE congeners), total PCDDs (summation of 7 PCDD congeners), total PCDFs (summation of 10 PCDF congeners) and total coplanar PCBs (summation of 12 non- and mono-ortho PCB congeners) in blubber samples of Indo-Pacific humpback dolphins were 4030, 0.191, 0.661 and 3000 ng/g lipid wt., respectively, and those in finless porpoises were 961, 0.0515, 0.254 and 349 ng/g lipid wt, respectively. Contaminant levels in humpback dolphins were significantly higher than those in finless porpoises with the exception of PCDFs. This pattern can be attributed to higher contaminant exposure in western Hong Kong waters and possibly to interspecific differences in physiological and related parameters including diet, body size, nutritive condition, age, and sex. The predominant PBDE congener in both species was BDE47, but considerable amounts of BDE209 were also detected in the samples. In addition, the PBDE levels measured in both cetacean species in this study were significantly higher than those reported in previous studies conducted in Hong Kong, indicating continuing release of PBDE flame retardants into the environment as a result of the production, use and disposal of electrical equipment in southern China. Total coplanar PCB concentrations were 3-4 orders of magnitude higher than PCDD/DF concentrations in all blubber samples analysed, and mono-ortho PCBs contributed more than 99% of the total coplanar PCBs in both species. In terms of toxic equivalents (TEQs), which can be used to compare levels of dioxins and related compounds, 2,3,4,7,8-pentachlorodibenzofuran, PCB169, PCB126 and PCB118 were the major congeners detected in both species. Humpback dolphins had a higher mean TEQ level (0.505 ng/g lipid wt.) with a higher proportion of coplanar PCBs than finless porpoises (0.113 ng/g lipid wt). Concentrations of PBDEs, PCDDs/DFs and coplanar PCBs were highly correlated with one another, and lower levels of these contaminants found in adult female suggested the possible transfer of these contaminants to offspring during pregnancy and lactation. This study also sought to examine the risks to local cetaceans of exposure to commercial PBDE mixtures (DE-71 and BDE209) and dioxins and related compounds. The results of the risk assessment showed that there was a potential risk of immunotoxicity to the local humpback dolphin population due to current exposure levels of the dominant PBDE congeners in DE-71, namely BDE47, BDE99, BDE100, and total TEQs, especially due to 2,3,4,7,8-PeCDF and PCB169. The contaminant burdens of these compounds in cetaceans from Hong Kong are of concern, and further investigation of potential health effects of these pollutant levels on the cetaceans is necessary. Extrapolation of the threshold effect levels in this study from other species and tissue types involves many uncertainties. Therefore the assessment should be refined further when more toxicological data on brominated flame retardants as well as dioxins and related compounds in marine mammals become available.

Thesis (M.Phil.)--City University of Hong Kong, 2008.