Concentrations of persistent organohalogen compounds in waterbird eggs in south China : method development and risk assessment

Abstract

Hong Kong, located at the mouth of the Pearl River in South China, receives persistent toxic contaminants into its marine habitats from a variety of sources including shipping activity, wastewater, industrial wastes and agricultural runoff. The rapid development of industrial and urban areas in the hinterland of the Pearl River Delta is also an increasingly important source of contaminants to Hong Kong, especially via riverine and aerial inputs. International negotiations to reduce and eliminate the emission and discharges of an initial set of twelve “persistent organic pollutants” (POPs) were initiated at the Stockholm Convention on Persistent Organic Pollutants in May 2001. The twelve substances that were addressed at the Stockholm Convention were: aldrin, endrin, dieldrin, dichlorodiphenyltrichoroethanes (DDTs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), chlordane, toxaphene, heptachlor, hexachlorobenzene (HCB) and mirex. However, the data regarding these compounds are incomplete or missing. It is important to have the basic or background information on these compounds in order to evaluate the policies carried out to reduce and eliminate the emission or discharge of these chemicals. Polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) are emerging compounds of concern. PBDEs are bioaccumulative and toxic in many toxicological animal tests, while perfluorooctane sulphonate (PFOS), one of the well-known PFCs of concern, is also suggested to be carcinogenic. It is also important to evaluate the occurrence and the degree of contamination in Hong Kong. Water birds are valuable and useful for environmental monitoring. They are particularly susceptible to environmental contaminants because they are long-lived and occupy the top trophic level of many food webs. Consequently, they are able to integrate pollutant levels over a broad area by bioaccumulation. Contaminant levels in water bird eggs, therefore, provide important and useful information for monitoring changes in environmental quality. The contamination status of the marine environment in Hong Kong was studied by the measurement of concentrations of these pollutants in the eggs of selected water bird species: Little Egret (Egretta garzetta), Chinese Pond Heron (Ardeola bacchus), Great Egret (Ardea alba), and Black-crowned Night Heron (Nycticorax nycticorax). The greatest mean concentrations of total polychlorinated biphenyls (PCBs) (4310 ng/g lipid wt.), total toxaphenes (295 ng/g lipid wt.), endrin (31.3 ng/g lipid wt.) and total chlordanes (975 ng/g lipid wt.) were detected in the eggs from Mai Po Village and were significantly greater than Night Heron eggs from A Chau. These results suggested spatial variation in the levels of contamination between the eastern and western waters of Hong Kong. Night Heron eggs from A Chau contained the lowest concentrations of most of the contaminants except for HCB (241 ng/g lipid wt.). Inter-species variation in feeding habitats, foraging distance and metabolism rate of birds likely resulted in the inter-specific variation in the contaminant concentrations in eggs of Night Heron and Great Egret from A Chau. The great proportion of p,p’-DDE and o,p’-DDE in the egg samples indicated that DDTs in the environment are probably from historical inputs. The risk characterization demonstrated the potential risks to birds associated with exposure to DDE, which was found to cause a reduction in survival of young in Hong Kong Ardeids. The greatest mean total PCDD/F concentration was found in Night Heron eggs from A Chau (PCDDs: 1020pg/g lipid wt. and PCDFs: 165pg/g lipid wt.), whereas lower concentrations were detected in egg samples of Little Egret and Chinese Pond Heron from Mai Po Village (PCDDs: 520pg/g lipid wt. and PCDFs: 167pg/g lipid wt.), and the least concentrations were found in egg samples of Chinese Pond Heron from Ho Sheung Heung (PCDD: 484pg/g lipid wt. and PCDF: 80.1pg/g lipid wt.). Eggs of Chinese Pond Heron and Little Egret from Mai Po Village had the greatest coplanar PCB concentrations, which were approximately two-to-three times greater than those of Chinese Pond Heron from Ho Sheung Heung and Night Heron from A Chau. Concentrations of PBDEs in Great Egret eggs in the present study were similar to those in Little Egret from Mai Po and Night Heron from A Chau. The absence of inter-specific and/or inter-site variations of PCDD/DFs, coplanar PCBs and PBDEs suggested the similar exposure levels of these contaminants to birds in northeastern and northwestern of Hong Kong. This finding further indicated the lesser importance of point source pollution over non-point source pollution because these contaminants come from a wide variety of human or industrial activities (e.g. incineration, combustion processes, and sewage treatment plants, as well as through chemical manufacturing processes of products containing related compounds), not from a single discharge point. The overall outcome of the risk characterization demonstrated that there are potential risks to birds associated with exposure to PCDD/Fs and BDE 99. Abnormalities in hatchlings and growth depression due to PCDD/Fs, and oxidative stress due to BDE 99 in eggs may be a potential cause for concern. Total concentrations of the 11 PFCs in waterbird eggs ranged from 27.0 ng/g ww in a Great Egret egg from Hong Kong to 160 ng/g ww in a Night Heron egg from Quanzhou. Significant differences in PFOS concentrations were found among species, but not among locations. The composition profiles of the individual PFCs among egg samples were generally similar. Preliminary risk assessment suggests that there is no immediate risk of a reduction in offspring survival in water birds in South China due to PFOS, but more information is needed on the potential effects of PFCs in water birds. Apart from studies on chemical analysis and risk evaluation of these chemicals to water birds in South China, an enzymatic digestion with solid phase extraction cleanup method on PFCs on biological tissues was developed to compensate for the limitations of the existing conventional extraction method (an ion pairing method) on biological tissues.