Quantification of the Influences of Environmental and Ecological Factors on the Distribution of PCBs in Fishes in a Tropical Estuary

• Main Authors: Chung-Te Fu, 傅崇德
• Other Authors: Shian-Chee Wu
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/97624835559143967216

博士 === 國立臺灣大學 === 環境工程學研究所 === 94 === Polychlorinated biphenyls (PCBs), a group of persistent organic pollutants (POPs), with high bioaccumulation potential and hazard to biota become a world-wide concern. Most previous studies were conducted in the regions where hydrological conditions and water qualities vary slightly compared to in the local estuaries in Taiwan, where water conditions fluctuate significantly. Also the climate in Taiwan is different from those in the temperate and sub-polar regions, which might lead to distinguishable distribution patterns of POPs in ecosystem. The severe contamination of PCBs in Er-Jen River in southwestern Taiwan in early 1990s has raised the concern of how and to what extent the PCBs has affected the ecological system in the estuary. To clarify the phenomenon of bioaccumulation in these biota and for further prediction of their PCBs body burden by quantification models, the purposes of this study are to unveil the origins of the PCBs and to distinguish the characteristics of food web biomagnification within the biota in the estuarine region. Furthermore, this study has also tried to develop a gastrointestinal tract magnifying model and a fugacity model to predict the body burden in biota. Additionally, a modified SPME technique has been applied to measure the activity of chemicals. To identify the origins of PCBs in the fishes residing in the estuary, this study has investigated some physicochemical parameters of the river system and PCB concentration of the river surface sediment and L. macrolepis before and after wet seasons in year 2002 to 2004. Obvious increment of PCB content and significantly elevated fraction (p < 0.005) of light PCBs of the river mouth’s sediments after each wet season indicates that the invading particles were rich in unweathered PCBs. PCBs previously buried in the soil of heavily contaminated sites were flushed into this estuary through surface runoff. Precipitation led to certain PCB patterns, significantly greater fraction of light PCBS in sediment organic matter, the dietary source of mullet, and consequently the same in mullets. The seasonal variation of the distribution of PCBs on surface sediments help us to establish the link between surface sediment and bottom dwellers. In addition to the hydrological variation, variation of PCB concentration among habitats has confirmed that the source of PCBs in biota was originally from the sediment. The PCB body burden of collected fish samples was proportional to the contamination level of their locations. Using the less chlorinated PCB fraction (triCB + tetraCB) / total PCBs as the indicator of the origins of PCBs, fish near former contaminated areas had greater body burdens of the more chlorinated PCB congeners, while the farmed fish exhibited a PCB pattern more like that known to originate from air-water exchange with less chlorinated PCBs predominating. The deviation of concentration and congener profile in the three habitats indicate that these variations are attributed to their habitats, and sediment was the most possible source of PCBs to fish. A modified SPME technique was applied to detect the aqueous equivalent content (AEC) of polychlorinated biphenyls in field samples. Indicated by the gradients of activities of concerned compartments, the bottom sediment was the source of contaminant in this estuary, and PCBs moved from buried sediment to surface sediment, to water column and finally to the biota. The fishes in this estuary included bottom dwellers such as C. chanos, M cephalus, L. macrolepis, N. come and A. maculates, and some pelagic dwellers such as M. cyprinoides, E. machnata, T. lepturus, S. putnamiae and M. cordyla.M. The bioaccumulation through food web in the bottom dwellers increased with their trophic levels, while for the pelagic dwellers the phenomenon was unseen. The biomagnification found only in these sediment-linked fishes suggests that the surface sediments are the main source of PCBs in the estuary. The biota to sediment accumulation factor (BSAF) of individual PCB congener was directly in proportional to their chlorination degree and increased with elevated trophic level, which indicates that the more hydrophobicity of the chemicals, the higher accumulation potential they will possess. The chemical with the highest accumulation potential was those with log KOW in the range 6.5 to 7.0. The trend decreases when log KOW exceeds 7. Biomagnification of the highly hydrophobic congeners are not increasing with their KOW. Structural hindrance and other unidentified factors may retard the partition of chemicals into the cells of biota. Predictions of the PCB concentration of total body burden and individual congeners were performed by the GIT biomagnification model and the simplified fugacity model. The possible slope of the predicting formula based on the GIT model, (r2 = 0.90), reveals the tendency of bioaccumulation of PCBs through trophic levels. The magnifying ratios of PCB congeners with log KOW range from 5.5 to 7.0 are around 1.4 to 3.8, similar to the findings in Gobas et al. (1993), but smaller than Gobas’s observation for the congeners whose log Kow are larger than 7.0. This was attributed to that the higher fugacities measured by Gobas were from the feces rather than the tissue, which led to an overestimation of magnifying ratio. The ratio between observed values and predicted values data from the simplified fugacity model, though in which numerous parameters are necessary, is close to 1.0 (1.33), which reveals the accuracy of the model. This study has not only established the exposure route of PCBs to fishes in a local estuary case, but also provided predicting models for the body burden of PCBs in fishes. These research results will considerably help on the risk management of POPs in local and other cases, setting criteria of sediment qualities and choosing sediment remediation approaches