利用MARA與Microtox生物試驗法評估垃圾焚化殘留物之毒性潛勢;Assessing toxicity of municipalsolid waste incineration residues with MARA and Microtox bioassays

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Title:	利用MARA與Microtox生物試驗法評估垃圾焚化殘留物之毒性潛勢;Assessing toxicity of municipalsolid waste incineration residues with MARA and Microtox bioassays
Authors:	蔡宗霖;Tsai, Tsung-Lin
Contributors:	環境工程研究所
Keywords:	生物毒性試驗;MARA;Microtox;焚化底渣及飛灰;toxicity bioassays;MARA;Microtox;municipal solid waste incinerator bottom ash and fly ash
Date:	2018-01-29
Issue Date:	2018-04-13 11:31:46 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究為瞭解焚化灰渣經碳酸鹽礦化此穩定化技術處理後的危害特性變化，除進行溶出試驗的重金屬分析外，也利用Microbial Assay for Risk Assessment (縮寫為MARA)與Microtox 兩種已商用套組化的生物毒性試驗法，進一步評估焚化灰渣經碳酸鹽礦化後在「生物層面」上的無害化成效。同時，本研究亦透過再現性、重複性及敏感度等指標評估兩方法應用在固體廢棄物相關研究的適用性，並試圖探討化學分析與生態毒理特性之間的關聯性，以瞭解灰渣溶出液毒性的來源及僅用化學分析是否已足夠做為固體廢棄物無害化的依據。試驗過程中可觀察到MARA 的培養液已具有酸鹼緩衝的能力，所以當此法應用在評估灰渣時，無需如同Microtox 那般需先對溶出液進行pH 值的調整，以排除因高鹼性所帶來的干擾。此外，在進行Microtox 檢測時觀察到並非所有的溶出液樣品對模式生物Vibrio fischeri 的毒性效應皆可在30 分鐘內達平衡，顯示後續的研究需留意此平衡時間上的判定，以免低估樣品真正的毒性效應。更值得注意的是，兩方法在灰渣碳酸鹽礦化前後的毒性判讀上最終出現相異的結果：以Microtox 檢測時發現碳酸鹽礦化前的灰渣樣品具有較高的毒性，但MARA 的結果卻顯示出碳酸鹽礦化後的灰渣所具有的毒性較高(此法所用的11 株菌種中，以#2 的Brevundimonas diminuta 及#9 的Pseudomonas aurantiaca 兩類菌種對溶出液最為敏感，而與高等生物在細胞結構與生理特性上最為接近的#11 Pichia anomalia 所受到的毒性衝擊卻不甚明顯)。由於兩種方法所用的培養液背景基質皆可能顯著影響重金屬的化學物種組成，進而影響其生物有效性程度，因此造成此差異性的機制尚待釐清，現階段無法明確評估兩種方法孰優孰劣。即使如此，以一般針對細菌性測試物種所訂定之20%濃度閥值來看，因灰渣在碳酸鹽礦化後的半數影響濃度(EC50)低於Microtox 之方法偵測極限，而經MARA 檢測後的微生物毒性濃度(MTC)也介於35.55-52.13%，故本研究經過碳酸鹽反應的灰渣與飛灰皆無法被歸類為是毒性樣品，對於生態應不致帶來顯著的負面衝擊。;This study investigated the change of potential hazards associated with preand post-stabilization of municipal solid waste incinerator (MSWI) residues, including bottom ash and fly ash. Both chemical and ecotoxicological characterization of leachates from residue TCLP were conducted: chemically, concentrations of regulated heavy metal species were quantified; toxicologically, commercial microbially-based bioassays were used to evaluate the toxicity of leachates, including Microbial Assay for Risk Assessment (MARA)- a battery test in which ten bacterial and one yeast species are incorporated, and Microtoxan in vitro testing system that employs a bioluminescent bacterium (Vibrio fischeri, aka Allivibrio fischeri) to detect toxic substances in samples. To gauge which bioassay would be more suitable for solid waste toxicity assessment, reproducibility, repeatability and sensitivity of the results obtained from both assays were compared. In addition, the correlation between chemical and ecotoxicological characteristics of the MSWI leachates was discussed. Over the course of experiments, it was found that due to the inherent buffer capacity of the assay medium, MARA did not require pH adjustment on samples; in contrast, acidification of samples to circumneutral pH was a necessitate for Microtox in order to eliminate the interference resulting from elevated hydroxide levels of MSWI residues. In addition, observable toxicity was not equilibrated in Microtox within 30 min that is often suggested by the protocol, indicating that to avoid underestimation of sample toxicity, appropriate exposure periods should be aware of. Notably, discrepancy was observed between these two assays with respect to toxicity change before and after stabilization of MSWI ash. Given that the matrix effect in the assay medium seems to play a critical role in governing the exhibited toxicity, at this point superiority of MARA over Microtox or vice versa is not ascertained. Regardless, results of this study showed that after carbonization, half effect concentrations (EC50) of the ash samples were too low to be detected in Microtox; further, the microbial toxic concentration (MTC) measured in MARA ranged from 35.55 to 52.13%, which exceeded the 20% threshold that is generally set for the bacterial toxicity assay. Accordingly, none of the bottom and fly ashes after carbonate mineralization in this study can be classified as toxic samples and may not significantly exert adverse ecotoxicity.
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