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Title: Evaluation of lysosomal integrity in green-lipped mussel (Perna viridis) as a biomarker in environmental monitoring
Other Titles: Fei cui yi bei de rong mei ti wan zheng du zuo wei sheng wu zhi biao zhi ping gu
Authors: Fang, Kar Hei (方家熙)
Department: Department of Biology and Chemistry
Degree: Master of Philosophy
Issue Date: 2007
Publisher: City University of Hong Kong
Subjects: Lysosomes.
Biochemical markers.
Notes: xx, 195 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2007.
Includes bibliographical references (leaves 155-182)
CityU Call Number: QH603.L9 F36 2007
Type: thesis
Abstract: Biomarkers are globally applied to detect spatial and temporal patterns of pollution/stress levels. It was argued that the initial and maximum responses induced by stress, as well as adaptation and recovery of these responses must be fully understood, otherwise erroneous interpretation and conclusions may be derived. Surprisingly, the vast majority of existing studies only focus on initial responses, while adaptation and recovery of biomarkers remains relatively unknown. Lysosomal integrity in mussels has been widely used as a cytological biomarker to detect pollution in coastal waters. In this thesis, the temporal changes of this biomarker in response to environmental stresses were studied in detail under both laboratory and field conditions, with a view to evaluating the current use of this biomarker in practical monitoring. In the first part of this study, the time required for induction, adaptation and recovery of lysosomal integrity in the green-lipped mussel (Perna viridis) upon exposure to benzo[a]pyrene (B[a]P) was investigated. Lysosomal integrity was significantly reduced by approximately 40% (maximum induction) after six days exposure but no further change (adaptation) was detected afterwards in an experimental period of 42 days. Gradual recovery was observed since mussels have been depurated in clean seawater after 18 days exposure, whereas complete recovery occurred in 20 days after depuration, with lysosomal integrity returned to background level, and stabilized afterwards, during the entire experimental period of 62 days. Significant correlation was found between changes in lysosomal integrity and body burden of B[a]P (r = 0.72). The fast induction and slow recovery suggested that lysosomal integrity in P. viridis is sensitive to pollution levels, and able to dampen short-term fluctuations of contaminants. The lack of apparent adaptation makes underestimation of pollution levels (false-negative) unlikely. The significant correlation between lysosomal integrity and the condition index of the mussels (r = 0.45) suggested that lysosomal integrity may serve as an early prognostic cytological marker prior to the occurrence of physiological impairment. This study further demonstrated that total ammonia-N and hypoxia could reduce lysosomal integrity (by circa 36%) in seven days, to an extent similar to that resulting from exposure to B[a]P. The fact that lysosomal integrity is equally sensitive to general water quality changes showed that great care must be exercised in relating the observed changes in lysosomal integrity to any specific pollutant. Since 2001, the government of Hong Kong has implemented the Harbour Area Treatment Scheme (HATS), which has removed 25% of the ammonia, 75% of the BOD and 85% of suspended solids from municipal sewage discharging into Victoria Harbour. As such, the water quality in the harbour and its vicinity is expected to improve. In the second part of this study, P. viridis were sampled bimonthly from six sites along the general harbour area during the period from July 2004 to July 2006. Lysosomal integrity in mussels was determined to detect possible improvement of water quality. This information was used in an attempted to correlate lysosomal integrity with the prevailing water quality parameters (i.e. ammonia-N, dissolved oxygen, temperature, salinity) and body burdens of ΣPAH and ΣPCB. The highest lysosomal integrity, corroborated with the lowest body burdens of ΣPAH and ΣPCB, was found at the cleanest site east to the harbour, where the highest DO and lowest ammonia-N concentrations were found. In contrast, the lowest lysosomal integrity, coupled with the highest body burdens of ΣPAH and ΣPCB, was found at Kung Tong inside the harbour with the lowest DO level and poor circulation. During the study period, significant improvement of lysosomal integrity (by 56% to 173%) was determined in mussels within the harbour and at an eastern site, indicating a general improvement in water quality after pollution abatement in these areas. However, the contrary was found in the body burdens of trace organics, in which a significant increase in ΣPAH was noted in mussels sampled from most sites whereas a decline in ΣPCB was registered. While lysosomal integrity was not affected by seasonal variations, approximately 56% of the variation of lysosomal integrity could be attributable to changes in ammonia-N, DO and body burden of ΣPAH in mussels (adjusted r2 = 0.56). In conclusion, lysosomal integrity demonstrates a good dose-response relationship with a wide range of stressors. The response of lysosomal integrity is consistent with field results, but it must be cautioned since the response can be confounded by ammonia and DO levels in the natural environment. Lysosomal integrity is a cost-effective, simple, reproducible and biologically relevant biomarker suitable for use in routine environmental monitoring.
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