| 摘要: | 本研究嘗試以土耕方式探討Chiou等人於2001年所提出的「有效土壤污染濃度」以及植作在土壤環境中對於有機污染物攝取的「分配限制模型」(partition-limited model)，並同時試著評估以固相微萃取(solid phase microextraction, SPME)此等被動採樣方法作為代表有機污染物於土壤介質之「生物有效性」(bioavailability)的可行性。植栽試驗的進行乃是將根系作物-白蘿蔔、胡蘿蔔、櫻桃蘿蔔，及葉菜類作物-青江菜，栽種於以壤土為基底混合腐植土/泥炭土所調配而成具有不同土壤有機質含量與不同有機污染物濃度的試驗土壤，待收成後分析土壤與植體食用部位的污染物含量，藉此探討分配模式中各參數與植作所受之實際污染程度間的關聯性為何，以了解土壤、污染物與植作三者間的交互作用，盼能合理預測污染物在土壤宿命中的行為與傳輸作用，進而作為場址整治時植生復育技術的選用以及預警的參考資訊。有機污染物包括多溴二苯醚(BDE-47, 77, 99, 100, 209)、六氯苯(HCB)，以及加保扶(carbofuran)。兩次植栽實驗的結果顯示：(1)以土壤有機質標準化後所得的污染濃度(Com)與傳統的土壤全量污染濃度(Cs)相比，前者更能代表植作攝取污染物的程度 (亦即實際的污染強度)，且在相同Cs污染濃度下多數植栽於低有機質土壤中的植作所累積的污染物濃度會高於栽種於高有機質土壤所測得的植體污染濃度，與「有效土壤污染濃度」之概念相呼應；(2)植體中所含低溴PBDEs的比例普遍高於土壤，暗示著溴數越低之PBDEs越易被根部吸收進而累積於植體；(3)青江菜比櫻桃蘿蔔更易攝取/累積BDE-209與carbofuran，顯示植體組成中的脂肪較其他組成分更具有主導親脂性溶質的吸收，使得非離子態有機污染物在植體的累積程度與其脂質含量有關；(4)模式計算所得之pt 值(準平衡因子)皆< 1，顯示植栽作物對於試驗用之目標污染物以被動傳輸為主要攝取方式，且pt值皆與污染物的Kow呈反比關係，代表污染物脂溶性越高，則pt值越小，越不易達到系統的分配平衡；(5)藉植作攝取BDE-209與HCB的濃度作為人體攝食途徑以評估攝入人體內的風險性時發現，當植作pt值越高且攝食量提高情況下，人體暴露在此環境下的風險也隨之提高，故或許可利用量測植作pt值作為預測風險的參考依據；(6)最後，SPME試驗因結果未能呈現同於實際植栽測得的濃度趨勢需再進一步測試其試驗方法，選擇適合吸附平衡之材質，且根據分配平衡理論推算的數值與植作實測值間的差異仍需進一步的探討。以上這些結果可看出，雖然本研究的植栽試驗無法直接從數據表明Com與Cpt之間的關係，但整體所觀察到的趨勢仍舊可以與「有效土壤污染濃度」以及「分配限制模型」背後的理論基礎相呼應。;This study intended to explore the concept of “SOM-based contamination effects of organic compounds with common soils” as well as the “partition-limited” model deciphering uptake of organic contaminants by the root of plants/crops proposed by Chiou in 2001 (DOI: 10.1021/es0017561) using pot experiments, and evaluate the feasibility of applying solid-phase microextraction (SPME), one of the passive sampling methods commonly used in studies of the aquatic system, to serve as a surrogate for bioavailability of organic pollutants in soil matrix. Experiments were carried out by cultivating root crops (i.e., white radish, carrot, and cherry radish) and leafy vegetables (i.e., pak-choi) in soil prepared by mixing loam and peat to form soil with varying soil organic matter (SOM) contents that contained different levels of organic compounds including PBDEs (i.e., BDE-47, 77, 99, 100, 209), hexachlorobenzene (HCB), and carbofuran. Concentrations of PBDEs, HCB, and carbofuran in soil and the edible part of harvested crops and vegetables were measured in order to probe the association between the organic contamination level and the soil contamination intensity. Results of the experiments showed that: (i) compared to the concentration in whole soil (Cs), not only did the SOM-based index (Com) provide better association with concentrations of target organic contaminants uptake and accumulation in plants (Cpt), contamination intensity in plants was higher in soil with low-SOM than with high-SOM for most of the plants under the same Cs, consistent with the “effective soil contamination” concept; (ii) the proportion of low-bromine PBDEs in carrots was generally higher than that in soil, suggesting that PBDEs with lower Kow were more easily taken up by plant roots; (iii) uptake of BDE-209 and carbofuran was relatively high in pak-choi to cherry radish, indicating that lipid was the major plant composition governing the accumulation of non-ionized organic pollutants in crops; (iv) all the values of pt (i.e., the quasi-equilibrium factor) obtained from this study were < 1, suggesting that passive transport indeed was the principal uptake pathway of hydrophobic organic compounds in plants; (v) elevated pt corresponded to higher exposure risks, implying that pt may potentially be used as an useful index for risk assessment; (vi) SPME unfortunately provided poor relationship between the soil contamination level and the contamination intensity in terms of adsorption quantity on fibers, which might be due to inappropriate operation and selection of the fiber adsorbent. Overall, results of this study reflected the concept of “SOM-based contamination effects of organic compounds with common soils” and agreed well with the trend predicted by “the partition-limited uptake model”. |
