二仁溪河口區域底泥重金屬初步生態風險評估

Screening Level Ecological Risk Assessment on Sediment-bound Heavy Metals in The Erhjen River Estuary, Taiwan

黃琦博(Chi-Po Huang)

指導教授 ： 洪慶宜

長榮大學/健康科學學院/職業安全與衛生學系(所)/碩士(2011年)

https://doi.org/10.6833/CJCU.2011.00224

摘要

二仁溪河口早期是台灣處理廢五金的主要場所，又長期以來承受流域內廢污水污染，金屬污染物可能蓄積在河川底泥中，經由食物鏈關係而影響整個水體生態環境。故本研究針對二仁溪河口底泥重金屬進行生態風險評估，應用X-光螢光分析儀 (X-ray Fluorescence Spectrometer, XRF )作為測量底泥重金屬含量工具，以地理資訊系統(GIS)來整理及分析數據，建立二仁溪河口底泥重金屬分布資料，並以probable effect level (PEL)為生態基準的風險商數法來初步推估二仁溪底泥重金屬的生態風險，以提供河川整治決策的參考。本研究並於颱風前後採樣，以評估河道沖積對底泥重金屬流布及生態風險的影響。兩次採樣所測得濃度均以Zn含量為最高，分別為217.7±136.3 mg•kg-1、254.4±313.3 mg•kg-1，Cu次之，分別為138.0±144.6 mg•kg-1、224.6±411.8 mg•kg-1，Hg及Cd大多低於XRF之偵測極限(分別低於10 mg•kg-1及12 mg•kg-1)。不同河段底泥重金屬含量不同，大致以三爺溪底泥重金屬污染最高。與底泥基準值PEL比較，二仁溪底泥重金屬數值大多高於生態基準，主要污染支流三爺溪及高灘地廢五金污染場址河段生態風險值較高，反映出底泥污染來源。二次採樣二仁溪的底泥Pb、As、Zn、Cu、Ni、Cr超過PEL生態基準的採樣點平均比例分別為4.53、10.7、9.67、4.01、80.2、23.0%，各重金屬中以Ni、Cr風險最高。考量Cu、Ni、Cr在XRF分析時的不確定性，依檢測標準底泥的回收率調整PEL基準值，Cu、Ni、Cr超過生態基準的採樣點平均比例分別降為2.05、6.56、3.17%，各重金屬中以As、Zn風險最高。颱風前後調查結果顯示沖積影響較污染源小。本研究結論二仁溪底泥重金屬可能造成底棲動物生態風險，重金屬濃度較高的河段需進一步以更詳細的底泥毒性試驗來確認進行底泥整治的必要性。

關鍵字

生態風險評估 ； 底泥 ； 重金屬 ； X-光螢光分析儀

並列摘要

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.

並列關鍵字

ecological risk assessment ； sediment ； heavy metal ； XRF

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