不同土壤中镍的离子活度研究
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摘要
自由离子浓度(或活度)是决定重金属的生物有效性和化学行为的关键因素,然而土壤系统中自由金属离子的活度测定与模型预测还存在很多不确定因素。该研究以重金属元素镍为研究对象,从它的固液分配系数、自由离子活度影响因素出发,通过经验的多元回归模型以及腐殖质平衡模型(WHAM VI)分析了影响其指标变化的关键因子。结果发现,土壤孔隙水的pH是影响镍在土壤固/液相分配的最关键因子,可以解释91%固液分配系数(K_d)的变化;同时,它也是影响自由镍离子活度占总镍百分比的最关键因子(r~2=0.74),土壤孔隙水中溶解性有机碳含量(DOC)可以提高回归模型的预测,但贡献率仅占10%。使用WHAM VI预测土壤孔隙水中自由镍离子活度的结果显示,采用惯用的65%活性富里酸(AFA)代替孔隙水中的活性DOM会导致预测值低于道南膜技术(DMT)测定值20%左右(碱性土壤除外),两者均方根误差(RMSE)达到15.7。分别降低碱性、中性、酸性土壤中的%AFA至50%、10%、5%,模型预测能力显著提高,预测值与实测值百分比的RMSE达到8.65。其研究结果说明土壤中的活性DOM比例较低(5%～50%),尤其对于中性与酸性土壤来说,活性DOM≤10%。该研究结果对于土壤系统的模型构建与重金属镍的环境风险评估具有重要意义。
Free nickel(Ni) species in soils is a key issue to its bioavailability. However, predictive models for Ni speciation across a wide range of soils are still unavailable. In this study, Ni distribution and its speciation in three contaminated soil samples are investigated via Donnan membrane dialysis technique(DMT) and predictive models. The results showed p H is the most important factor affecting distribution of Ni in soil solid and liquid. Also, pH is also the most key parameter explaining the percentage of free Ni~(2+) to total dissolved Ni in soil pore water. According to model, most of free Ni~(2+) fraction was underestimated when using default log K_(NiFA) and 65% active fulvic acid(AFA) as inputs in WHAM VI, especially for neutral and acidic soils. The best prediction was found when using adjusted %AFA with 5% for acidic soil, 10% for neutral soil and 50% for alkaline soil with the smallest RMSE = 8.65 and biggest r~2= 0.74. Decreasing binding constant of FA to Ni would not help model to improve the prediction for free Ni~(2+) fraction significantly. The study presents a comprehensive database of Ni speciation and an effective attempt of free Ni~(2+) prediction in classical Chinese soils.
Free nickel(Ni) species in soils is a key issue to its bioavailability. However, predictive models for Ni speciation across a wide range of soils are still unavailable. In this study, Ni distribution and its speciation in three contaminated soil samples are investigated via Donnan membrane dialysis technique(DMT) and predictive models. The results showed p H is the most important factor affecting distribution of Ni in soil solid and liquid. Also, pH is also the most key parameter explaining the percentage of free Ni~(2+) to total dissolved Ni in soil pore water. According to model, most of free Ni~(2+) fraction was underestimated when using default log K_(NiFA) and 65% active fulvic acid(AFA) as inputs in WHAM VI, especially for neutral and acidic soils. The best prediction was found when using adjusted %AFA with 5% for acidic soil, 10% for neutral soil and 50% for alkaline soil with the smallest RMSE = 8.65 and biggest r~2= 0.74. Decreasing binding constant of FA to Ni would not help model to improve the prediction for free Ni~(2+) fraction significantly. The study presents a comprehensive database of Ni speciation and an effective attempt of free Ni~(2+) prediction in classical Chinese soils.
引文
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[15]Nolan A L,McLaughlin M J,Mason S D.Chemical speciation of Zn,Cd,Cu,and Pb in pore waters of agricultural and contaminated soils using Donnan dialysis[J].Environmental Science and Technology,2003,37:90-98.
[16]SauvéS,Hendershot W,Allen H E.Solid-solution partitioning of metals in contaminated soils:dependence on pH,total metal burden,and organic matter[J].Environmental Science and Technology,2000,34:1125-1131.
[17]Ponizovsky A A,Allen H E,Ackerman A J.Effect of field aging on nickel concentration in soil solutions[J].Communications in Soil Science and Plant Analysis,2008,39:510-523.
[18]Vulkan R,Zhao F J,Barbosa-Jefferson V,et al.Copper speciation and impacts on bacterial biosensors in the pore water of copper-contaminated soils[J].Environmental Science and Technology,2000,34:5115-5121.
[19]Stockdale A,Tipping E,Lofts S.Dissolved trace metal speciation in estuarine and coastal waters:comparison of WHAM/Model VII predictions with analytical results[J].Environmental Toxicology and Chemistry,2015,34:53-63.
[20]Amery F,Degryse F,Degeling W,et al.The copper-mobilizing potential of dissolved organic matter in soils varies10-fold depending on soil incubation and extraction procedures[J].Environmental Science and Technology,2007,41:2277-228.
[21]Ahmed I A M,Hamilton-Taylor J,Bieroza M,et al.Improving and testing geochemical speciation predictions of metal ions in natural waters[J].Water Research,2014,67:276-291.
[22]Ren Z L,Tella M,Bravin M N,et al.Effect of dissolved organic matter composition on metal speciation in soil solutions[J].Chemical Geology,2015,398:61-69.
[2]Li B,Zhang X,Wang X D,et al.Refining a biotic ligand model for nickel toxicity to barley root elongation in solution culture[J].Ecotoxicology and Environmental Safety,2009,72:1760-1766.
[3]Van Laer L,Smolders E,Degryse F,et al.Speciation of nickel in surface waters measured with the Donnan membrane technique[J].Analytica Chimica Acta,2006,578:195-202.
[4]Li B,Ma Y B,Yang J X.Is the computed speciation of copper in a wide range of Chinese soils reliable[J].Chemical Speciation&Bioavailability,2017,29:205-215.
[5]Weng L P,Lexmond T M,Wolthoorn A,et al.Phytotoxicity and bioavailability of nickel:chemical speciation and bioaccumulation[J].Environmental Toxicology and Chemistry,2003,22:2180-2187.
[6]Nolan A L,Ma Y B,Lombi E,et al.Speciation and isotopic exchangeability of nickel in soil solution[J].Journal of Environmental Quality,2009,38:485-492.
[7]Tipping E,Rieuwerts J,Pan G,et al.The solid-solution partitioning of heavy metals(Cu,Zn,Cd,Pb)in upland soils of England and Wales[J].Environmental Pollution,2003,125:213-225.
[8]Milne C J,Kinniburgh D G,van Riemsdijk W H,et al.Generic NICA-Donnan parameters for metal-ion binding by humic substances[J].Environmental Science and Technology,2003,37:958-971.
[9]Guo X Y,Zuo Y B,Wang B R,et al.Toxicity and accumulation of copper and nickel in maize plants cropped on calcareous and acidic field soils[J].Plant and Soil,2010,333(1/2):365-373.
[10]Zarcinas B A,McLaughlin M J,Smart M K.The effect of acid digestion technique on the performance of nebulization systems used in inductively coupled plasma spectrometry[J].Communications in Soil Science and Plant Analysis,1996,27:1331-1354.
[11]Li B,Zhang H T,Ma Y B,et al.Relationships between soil properties and toxicity of copper and nickel to bok choy and tomato in Chinese soils[J].Environmental Toxicology and Chemistry,2013,32:2372-2378.
[12]Thibault D H,Sheppard M I.A disposable system for soil pore-water extraction by centrifugation[J].Communications in Soil Science and Plant Analysis,1992,23:1629-1641.
[13]Salam A K,Helmke P A.The pH dependence of free ionic activities and total dissolved concentrations of copper and cadmium in soil solution[J].Geoderma,1998,83:281-291.
[14]Oorts K,Bronckaers H,Smolders E.Discrepancy of the microbial response to elevated copper between freshly spiked and long-term contaminated soils[J].Environmental Toxicology and Chemistry,2006,25:845-853.
[15]Nolan A L,McLaughlin M J,Mason S D.Chemical speciation of Zn,Cd,Cu,and Pb in pore waters of agricultural and contaminated soils using Donnan dialysis[J].Environmental Science and Technology,2003,37:90-98.
[16]SauvéS,Hendershot W,Allen H E.Solid-solution partitioning of metals in contaminated soils:dependence on pH,total metal burden,and organic matter[J].Environmental Science and Technology,2000,34:1125-1131.
[17]Ponizovsky A A,Allen H E,Ackerman A J.Effect of field aging on nickel concentration in soil solutions[J].Communications in Soil Science and Plant Analysis,2008,39:510-523.
[18]Vulkan R,Zhao F J,Barbosa-Jefferson V,et al.Copper speciation and impacts on bacterial biosensors in the pore water of copper-contaminated soils[J].Environmental Science and Technology,2000,34:5115-5121.
[19]Stockdale A,Tipping E,Lofts S.Dissolved trace metal speciation in estuarine and coastal waters:comparison of WHAM/Model VII predictions with analytical results[J].Environmental Toxicology and Chemistry,2015,34:53-63.
[20]Amery F,Degryse F,Degeling W,et al.The copper-mobilizing potential of dissolved organic matter in soils varies10-fold depending on soil incubation and extraction procedures[J].Environmental Science and Technology,2007,41:2277-228.
[21]Ahmed I A M,Hamilton-Taylor J,Bieroza M,et al.Improving and testing geochemical speciation predictions of metal ions in natural waters[J].Water Research,2014,67:276-291.
[22]Ren Z L,Tella M,Bravin M N,et al.Effect of dissolved organic matter composition on metal speciation in soil solutions[J].Chemical Geology,2015,398:61-69.