| Summary: | 碩士 === 長榮大學 === 職業安全與衛生學系碩士班 === 99 === As the site of historical scrap metal industrial park in 70s to 90s and the receving water body of municipal and industrial wastewater, the Erhjen River esturary may be contaminated by heavy metals. By its particle affiliated nature, those metals are likely accumulated in sediment and threatened the aquatic wildlife through food chain. The purpose of this study was to conduct a screen-level ecological risk assessment on the sediment-bound metals in the Erhjen River estuary. By applying rapid-measuring X-ray fluorescence analyzer (XRF) to assess the metal contains of a large quantity of sediment samples as well as geographic information system(GIS) to present and analyze the data, sediment-bound Zn, Cu, Pb, Cd, Ni, As, Hg distributions in the 8-km lower reaches of the river were established. The samplings were conducted before and after the raining season, including a major Typhoon Morakot which badly flooding the esturary watershed, to assess the alluvial effect on the metal distributions and ecological risk. The results of sedimentary metal measurements showed that Zn concentration was the highest (217.7±136.3 mg•kg-1)、(254.4±313.3 mg•kg-1), followed by Cu (138.0±144.6 mg•kg-1)、(224.6±411.8 mg•kg-1), while Hg and Cd were mostly lower than the detection limit (<10 and 12 mg•kg-1, repectively) among the metal measured. Sedimentary metal contains were varied among different river segments. In general, the metal contains were highest in Sanye tributary segment, with an exception of As. The risk was calculated by comparing the sediment exposure profiles with the ecotoxicological benchmarks, Probable Effect Level(PEL) , for benthic organisms. Inverse-distance-weighing based maps of the spatial distribution of the estimated risk for the benthic community over the 8-km lower reaches of the river were obtained. The highest risk, found in the areas nearest to the sources of contamination (e.g., the major contaminated tributary and the historical scrap metal abandon site). The average frequency of exceeding ecological risk criteria, PEL, for sedimentary Pb, As, Zn, Cu, Ni, Cr were 4.53, 10.7, 9.67, 4.01, 80.2, 23.0% respectively. Ni and Cr posed the largest threat to benthic animals among heavy metals. However, considering the uncertainty of XRF estimation of Cu, Ni, Cr, adjustments were made on the ecological risk criteria to compensate the potential overestimation of risks based on the recovery of standard reference sediment estimated by XRF. The average frequency of exceeding ecological risk criteria for sedimentary Cu, Ni, Cr decreased to 2.05, 6.56, 3.17%, respectively. As and Zn became the most dangerous heavy metals among all.The alluvial effect was less significant comparing with pollution source on the sedimentary sediment distribution. This study concluded that the heavy metals have posed a ecological risk to the benthic animals in the Erhjin River esturary. Further sediment toxicity test was recommended to assess the necessity of sediment contamination cleanup action.
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