摘要
随着城市化、工业化的快速发展和化肥、农药的大量施用,大量重金属污染物直接或间接的进入农田土壤。外源重金属铅(Pb)、镉(Cd)污染物进入土壤后,随时间的延长,在土壤中的有效性降低,有效态含量趋于稳定。这一过程受到土壤质地、阳离子交换量(CEC)、有机质、pH等因素的影响。对于单一因素的影响机理前人已有研究,但土壤是一个复杂的多相体系,各种因素并存且相互作用,因此对自然状态下,各种因素对重金属污染物在土壤中稳定化过程的综合作用研究,将更有实际意义。
本研究利用室内培养实验,在27个土样中人为加入Pb.Cd盐溶液,于污染后的第2、7、15、30、60、90、180、270、360天采样,用0.5mol·L-1MgCl2提取有效态,通过动力学方程模拟单一及复合污染条件下土壤中外源Pb、Cd的稳定化过程,选取最优模型,并得到表征土壤中Pb、Cd稳定化过程的参数;通过回归分析、通径分析研究了不同土壤性质(CEC、有机质含量、颗粒组成、pH)对重金属稳定化过程的影响的大小,并确定主要影响因子。得出以下结果:
1)加入500 mg·kg-1 Pb、1.0 mg·kg-1 Cd或1.0 mg·kg-1 Cd+500 mg·kg-1 Pb条件下,有效Pb、Cd含量在培养前期迅速减少,随后减少速率变缓,培养30天后趋于平衡。培养360天时,有效态铅、镉含量约为培养2天时的30%-70%。不同土壤中有效态Pb、Cd含量差异很大,一般在pH较低的红壤中,有效态Pb、Cd含量较高;在pH较高的潮土、褐土、黑色石灰土等土壤中,有效态Pb、Cd含量较低。取自长期定位实验点的红壤、潮土、黑土等19个土样,施有机肥处理的NPKM、1.5NPKM等土样,由于pH较高,有机质含量较高,有效Pb、Cd含量一般都低于施化肥的N、NP和NPK等土样。
2)利用一阶指数衰减函数、Elovich方程、二级动力学方程和双常数方程模拟外源Pb、Cd在土壤中的稳定化过程。27个土样的有效态Pb、Cd随培养时间变化都以二级动力学方程和一阶指数方程的模拟结果较好,模拟方程的决定系数均达到极限显著水平(R2>0.90),其中,二级动力学方程模拟的决定系数最高,为最优模型。双常数方程模拟的决定系数在0.53-0.93之间,也都达到显著水平。Elovich方程模拟的结果相对较差,尤以对红壤NPK、砂岩红壤、赤红壤、黑土PK、黑土NPKM上Pb稳定化过程的模拟结果最差。
3)通过二级动力学方程模拟得出的平衡浓度y0值可知,Pb单一污染中以花岗岩红壤的y0值最高(239 mg·kg-1),黑色石灰土最低(0.360 mg·kg-1). Cd单一污染中,以红壤NP的y0值最高(0.554 mg·kg-1),黑色石灰土最低(0.093 mg·kg-1)。Pb-Cd复合污染中,除了黑土NPK、黑土1.5NPKM和砂岩红壤外,外源Pb的加入提高了土壤中有效Cd的含量,增加了其环境危害。外源Cd的加入对土壤Pb的浓度没有显著的影响,这与Cd的竞争力弱于Pb,以及Cd的加入浓度(lmgCd/kg土)非常低有关。
4)双常数方程得出的速率常数B值反映了土壤重金属污染物随时间延长而降低得快慢,B值越大,稳定化进程越快,反之则越慢。Pb稳定化过程的B值以黑色石灰土最高(0.482),红壤N最低(0.051);Cd稳定化过程的B值也以黑色石灰土最高(0.216),红壤N最低(0.055)。在Pb或Cd单一污染下,红壤的稳定化速率总体比黑土、潮土较慢。Pb-Cd复合污染下,Pb或Cd稳定化速率受离子间交互作用的影响,在不同土壤有很大的差异。
5)不同土壤性质影响了Cd、Pb稳定化过程的速率和平衡浓度。通径分析表明,土壤pH是影响稳定化过程中Cd、Pb平衡浓度的主要因素,表现为土壤pH增加可以有效地降低Cd、Pb的活性,使其环境的毒害作用减小。阳离子交换量和粘粒含量对Cd、Pb平衡浓度也有一定影响,但都是通过pH变化实现的。土壤有机质和pH是影响Cd、Pb稳定化速率的主要因素。随着有机质和pH的提高,土壤Cd、Pb稳定化速率不断加快。阳离子交换量的增加也能够在一定程度上加快Cd、Pb稳定化的进程,而粘粒含量对稳定化速率影响较小。
With the rapid development of urbanization and industrialization, a large number of chemical fertilizer and pesticide application and many heavy metal pollutants were carried into the farmland soil directly or indirectly. The availability of lead (Pb) or cadmium (Cd) would decreased with the time after the polllutants of Pb or Cd was added into the soil, this process was affected by soil mechanical composition, cation exchange capacity(CEC), organic matter, pH, and so on. Some research about the single factor have been done, but the soil as a complicated heterogeneous system with various factors existing and interacting, it would have more practical significance to research the effect of soil properties on the stabilization processes of Cd and Pb in the natural conditions.
The stabilization processes of Cd and Pb in single and combined metal-contaminated soil of China were studied. MgCl2 extraction was employed to examine the available speciation of Cd, Pb in soils. Cd, Pb or their mixture were added into twenty-seven soil samples respectively. Each treatment were sampled at 2rd,7th,15th,30th,60th,90th,180th, and 360th day after pollution and then extracted using 0.5 mol·L-1 MgCl2. Four kinds of dynamical equations were used to simulate the stabilization process of Cd or Pb, then, the optimum fitting equation was selected, the parameters modeled by dynamical equations about the stabilization processes of Cd and Pb were gained. By means of regression analysis and path analysis, the effect of different soil properties (CEC, organic matter, soil mechanical composition and pH) on the stabilization processes of Cd and Pb was researched, the most important factor was confirmed. The results had been drawn as follows:
1) After 500 mg·kg-1 Pb,1.0 mg·kg-1 Cd or 500 mg·kg-1 Pb+1.0 mg·kg-1 Cd were added in soil, soil availability of Pb and Cd were decreased rapidly during the first some days, then, decreased slowly, and stabilized after 30 day's incubation. The differences of content of available Pb or Cd in the 27 soil samples were very significant, generally, in the red soil with low pH, the content of available Pb or Cd was higher, while, in the soil samples with high pH, such as fluvo-aquic soils, cinnamon soil, black limestone soil and so on, the content of available Pb or Cd was lower. In the red soil, black soil and fluvo-aquic soil, which taken from the long-term positioning sites, the content of available Pb or Cd in the NPKM and 1.5NPKM treatment with the high pH and high organic matter content were lower than that in the N, NP, and NPK treatment.
2) The stabilization process of Cd and Pb in the soil were simulated by first-order exponential decay function, second-order equation, Elovich equation, and two-constant equation. The second-order equation and first-order exponential decay function perfectly described the changes of available Pb and Cd with incubation time in the 27 soil samples, the correlation coefficients of the equations came up to the most significant standard (r>0.90), and the second-order equation was the optimum model, because its correlation coefficients was the highest. Then, the correlation coefficients of two-constant were between 0.53 to 0.93, all reached the significant standard. Elovich equation was the worse model than other models, especially, in red soil NPK treatment, Red sandstone, lateritic red earths, black soil PK treatment and NPKM treatment, the equation describing stabilization process of Pb in these soils were worst.
3) The equilibrium concentration (y0) can be gained by the second-order equation. In the group of single Pb contaminated soils, the value of yo was highest in granitization red soil (239 mg·kg-1),while it was lowest in black limestone soil(0.360 mg·kg-1). In the group of single Cd contaminated soils, the value of yo was highest in red soil NP treatment (0.554 mg·kg-1), while it was lowest in black limestone soil (0.093 mg·kg-1). In the Pb-Cd combined metal-contaminated soils, the existing of Pb increased the content of availability of Cd, except in black soil NPK treatment, black soil 1.5NPKM treatment and red sandstone, this would increase the harmfulness of Cd in the environmental. Whereas these had no significant effect of Cd on the availability of Pb, perhaps, it was because that the competitiveness of Cd was weaker than Pb and it had some related to the low concentration of added Cd.
4) The stabilization velocity (B), which obtained from the two-constant equation, reflected the rate of content of available heavy metal decreasing with the time. The value of B was larger, the velocity of stabilization process was faster; if not, the velocity of stabilization process would lower. In the group of Pb, the value of B was largest in black limestone soil(0.482), while it is least in the red soil N treatment (0.051), In the group of Cd, the value of B also was largest in black limestone soil(0.216), while it was least in the red soil N treatment (0.055). In the single Pb or Cd contaminated soils, generally, the stabilization velocity was slower in the red soils than that was in the black soils and fluvo-aquic soils. In the Pb-Cd combined contaminated soils, the stabilization velocity of Pb or Cd was affected by the interaction of ions, so it had large diversity between different soils.
5) The stabilization velocity and equilibrium concentration of Cd or Pb were influenced by soil properties. Path analysis indicated that pH contributed greatly to affect the equilibrium concentration of Cd or Pb in the stabilization process, showed that the increase of pH could reduce effectiveness of Cd or Pb, reduced the risk of environmental pollution in agricultural production. CEC and clay content also had some effect on the equilibrium concentration of Cd and Pb, but it were realized by the pH. The organic matter and pH were the major factors of affecting the stabilization velocity of Cd and Pb, with the increasing content of organic matter and pH, the stabilization velocity of Cd and Pb accelerated. To some extent, the increasing of CEC also could quickened the stabilization process of Cd and Pb, but the clay content had little effect on the stabilization velocity.
引文
[1]陈炳卿,孙长颢.食品污染与健康[M].北京:化学工业出版社,2002,149-152
[2]张辉,马东升.公路重金属污染的形态特征及其解吸、吸持能力探讨[J].环境化学,1998,17(6):564-568
[3]李宗利,薛澄泽.污灌土壤中Pb、Cd形态的研究[J].农业环境保护,1994,13(4):152-157.
[4]郝汉舟,陈同斌,靳孟贵,等.重金属污染土壤稳定化修复技术研究进展[J].应用生态学报,2011,22(3):816-824
[5]McLaughlin M.J. Aging of metals in soils changes bioavailability[J]. Environment Risk Assessment,2001,4(1):1-5
[6]Marti'nez C.E., Jacobson A.R., McBride M.B. Aging and temperature effects on DOC and elemental release from a metal contaminated soil[J]. Environmental Pollution,2003,122(1): 135-143
[7]Alexander M. Aging bioavailability and overestimation of risk from environmental pollutants[J]. Environmental Science & Technolog,2000,34(20):4259-4265
[8]Ford R.G., Bertsch P.M., Farley K.J. Changes in transition and heavy metal partitioning during hydrous iron oxide aging[J]. Environmental Science Technology,1997,31(10):2028-2033
[9]涂从.土壤体系中的化学动力学方程及其应用[J].热带亚热带土壤科学,1994,3(3):175-182
[10]徐明岗.土壤离子吸附3.离子吸附的动力学[J].土壤肥料,1998(1):3-6
[11]魏俊峰,吴大清,彭金莲,刁桂仪.污染沉积物中重金属的释放及其动力学[J].生态环境,2003,12(2):127-130
[12]陈苏,孙丽娜,晁雷.不同浓度组合的镉、铅在不同污染负荷土壤中的吸附-解吸动力学行为[J].2007,15(1):32-44
[13]张增强,张一平,朱兆华.镉在土壤中吸持的动力学特征研究[J].环境科学学报,2000,20(3):370-375
[14]李鱼,刘亮,董德明,等.城市河流淤泥中重金属释放规律的研究[J].水土保持学报,2003,17(1):125-127
[15]张再利,况群,贾晓珊.花生壳吸附Pb、Cu、Cr、Cd、Ni的动力学和热力学研究[J].生态环境学报,2010,19(12):2973-2977
[16]HO Y S, Mckay G. Pseudo-second order model for sorption processes[J]. Process Biochem,1999, 34:451-465
[17]陈灿,王建龙.酿酒酵母吸附Zn2+的特性及其动力学研究[J].清华大学学报:自然科学版,2006,46(12):2069-2072
[18]徐明岗,王宝奇,周世伟.外源铜锌在我国典型土壤中的老化特征[J].环境科学,2008,29(11),3213-3218
[19]田园,王晓蓉,林仁漳.土壤中镉铅锌单一和复合老化效应的研究[J].农业环境科学学报,2008,27(1):156-159
[20]Bruemmer,G W,Gerth J,Tiller K G. Reaction kinetics of the adsorption and desorption of nickel,zinc,and cadmium by goethite.I.Adsorption and diffusion of metals[J]. J Soil Sci,1988,39: 37-52
[21]Sauve S, Mcbride M B,Hendershot,W H. Lead phosphate solubility in water and soil suspensions[J]. Environ Sci Technol,1998,32:388-393
[22]Sauve S, Mcbride M B, Hendershot, W H.. Soil solution speciation of lead:Effects of organic matter and pH[J]. Soil Sci Soc Am J,1998,62:618-621
[23]Basta N T, Taba TABAItabai M A. Effect of cropping systems on adsorption of metals by soils: II.Effect of pH[J]. Soil Sci,1992,153(3):195-204
[24]王海燕,吴晓芙,胡日利.土壤镉活度模型与控制相研究[J].中南林学院学报,2000,20(2):1-6
[25]Gray C.W., McLaren R.G., Roberts A.H.C. Sorption and desorption of cadmium from some New Zealand soil effect of pH and contact time[J]. Australian Journal of Soil Research 1998,36: 199-216
[26]Garcia-Miragaya J., Page A.L. Sorption of trace quantities of cadmium by soilswith different chemical and mineralogical composition[J]. Water, A ir, and Soil Pollution 1978,9:289-299
[27]Benjamin M.M., Leckie J. O. Multiple-site adsorption of Cd, Cu, Zn and Pb on amorphous iron oxyhydroxide[J]. Journal of Colloid Interface Science 1981b,79:209-221
[28]张淼,李亚青,王敏新.黄土体对重金属(Cd、Pb、Zn、 Cu)吸附试验研究[J].西北水资源与水工程,1996,7(2):35-40
[29]王孝堂.土壤酸度对重金属形态分配的影响[J].土壤学报,1991,28(1):103-107
[30]武玫玲.土壤矿质胶体的可变电荷表面对重金属离子的专性吸附[J].土壤通报,1985,16(2):89-94
[31]宗良纲,徐晓炎.土壤中镉的吸附解吸研究进展[J].生态环境,2003,12(3):331-335
[32]孙卫玲,赵蓉,张岚,等.pH对铜在黄土中吸持及其形态的影晌[J].环境科学,2001,2(3):78-83
[33]于天仁,季国亮,丁昌璞,等.可变电荷土壤的电化学[M].北京:科学出版社,1996:65-85
[34]Harter RD, Naidu R. Role of metal-organic complexation in metal sorption by soils[J]. Adv. Agron.1995,55:219-263
[35]焦文涛,蒋新,余贵芬,等.土壤有机质对镉在土壤中吸附-解吸行为的影响[J].2005,24(5):545-549
[36]McBride M, et al. Soil Sci. Soc. Am. J,1998,62:1542-1548
[37]Spark K M, et al. Australian Journal of Soil Research,1997,35(1):113-122
[38]林琦,陈怀满.有机酸对Pb、Cd的土壤化学行为和植株效应的影响[J].应用生态学报,2001,12(4):619-622
[39]陈同斌.水溶性有机质对土壤中镉吸附行为的影响应用生态学报[J],2002,13(2):183-186
[40]余贵芬,蒋新,孙磊,等.有机物质对土壤镉有效性的影响研究综述[J].生态学报,2002,22(5):771-776.
[41]杨金燕,杨肖娥,何振立,等.土壤中铅的吸附-解吸行为研究进展[J].生态环境,2005,14(1):102-107
[42]Clemente R, Bernal M P. Fractionation of heavy metals and distribution of organic carbon in two contaminated soils amended with humic acids[J]. Chemosphere,2006,64(8):1264-1273
[43]Mench M, Bussiere S, Boisson J, et al. Progress in remediation and revegetation of the barren Jales gold mine spoil after in situ treatments[J]. Plant and Soil,2003,249(1):187-202
[44]Ruttens A, Colpaert J V, Mench M, et al. Phytostabilization of a metal contaminated sandy soil. Ⅱ:Influence of compost and or inorganic metal immobilizing soil amendments on metal leaching[J]. Environmental Pollution,2006,144(2):533-539
[45]鲁如坤,时正元,雄礼明.我国磷矿磷肥中镉的含量及其生态环境影响的评价[J].土壤学报,1992,29(2):150-157
[46]Naidu R and Harter R D. Effect of different organic ligands on cadmium sorption by and extractability from soils[J]. Soil Sci. Soc. A m. J.,1998,62:644-650
[47]Appel C., Ma L. Concentration, pH, and surface charge effects on cadmium and lead sorption in three tropical soils[J]. Journal of Environmental Quality,2002,31(2):581-589
[48]CHIP APPLE,LENA M A.. Concentration,pH, and surface charge effects on Cadmium and Lead sorption in three tropical soils[J]. Environ Qual,2002,31(4):581-589
[49]BASTA N T,TABATABAI M A. Path-analysis of heavy metal adsorption by soil[J]. Agron J,1993, 85(5):1054-1057
[50]杨秀红,胡振琪,张迎春.利用工业矿物治理重金属污染土壤的探讨[J].金属矿山,2003(3),52-55.
[51]李恋卿,潘根兴,张平究,等.植被恢复对退化红壤表层土壤颗粒中有机碳和Pb、Cd分布的影响[J].生态学报,2001,21(11):1669-1774
[52]刘云国,黄宝荣,练湘津,等.士壤化学萃取修复技术影响因素分析[J].湖南大学学报,2005,32(1):95-98
[53]Saha UK, Taniguchi S, Sakurai K. Simultaneous adsorption of cadmium, zinc, and lead on hydroxyalumium-and hydroxyaluminosilicate-montmorillonite complexes[J]. Soil Sci. Soc. Am. J, 2002,66:117-128
[54]Gomes PC, Fontes MPF, Silva AG, Mendonca ES, Netto AR. Selectivity sequence and competitive adsorption of heavy metals by Brazilian soils[J]. Soil Sci. Soc. Am. J.,2001,65: 1115-1121
[55]Fontes MPF, Matos AT, Costa LM, Neves JCL. Competitive adsorption of zinc, cadmium, copper and lead in three highly weathered Brazilian soil. Commun[J]. Soil Sci. Plant Anal.,2000,31: 2939-2958
[56]Saha UK, Taniguchi S, Sakurai K. Simultaneous adsorption of cadmium, zinc, and lead on hydroxyalumium- and hydroxyaluminosilicate-montmorillonite complexes[J]. Soil Sci. Soc. Am. J,2002,66:117-128
[57]Benjamin MM, Leckie JO. Competitive adsorption of Cd, Cu, Zn, and Pb on amorphous iron oxyhydroxide[J]. Colloid Interf. Sci.,1981,83:410-419
[58]Basta NT, Tabatai MA. Effect of cropping systems on adsorption of metals by soils:Ⅲ. Competitive adsorption[J]. Soil Sci.,1992,153:331-337
[59]Zhu B, Alva AK. Differential adsorption of trace metals by soils as influenced by exchangeable cations and ionic strength[J]. Soil Sci.,1993,155:61-66
[60]Bozkurt S, Moreno L,Neretnieks I. Long term processes in waste deposits[J]. Science of the Total Environment,2000,250:101-121
[61]刘景,吕家珑,徐明岗,等.长期不同施肥对红壤Cu和Cd含量及活化率的影响[J].生态环境学报,2009,18(3):914-919
[62]Yuan C, Jiang G, Liang k, et al. Sequential extraction of some heavy metal in Haihe River sediments[J]. People's Republic of China Bull Environ Contain Toxicol,2004,73:59-66
[63]柴世伟,温琰茂,张云霓.广州郊区农业土壤重金属含量与土壤性质的关系[J].农村生态环境,2004,20(2):55-58
[64]王新,周启星.外源镉铅铜锌在土壤中形态分布特性及改良剂的影响[J].农业环境科学学报,2003,22(5):541-545
[65]史锟,徐虹,田艳芬.酸和有机质对土壤镉影响的研究[J].垦殖与稻作,2003,(2):30-34
[66]Lock K, Janssen C R. Influence of aging on metal availability in soils[J]. Reviews of Environmental Contamination and Toxicology,2003,178(1):1-21
[67]鲁如坤.土壤农业化学分析方法[M].北京:中国农业科技出版社,2000
[68]普锦成,符娟林,章明奎.土壤性质对水稻土中外源镉与铅生物有效性的影响[J].生态环境,2008,17(6):2253-2258
[69]陕红,刘荣乐,李书田.施用有机物料对土壤镉形态的影响[J].植物营养与肥料学报2010,16(1):136-144
[70]Fontes MPF and Gomes PC. Simultaneous competitive adsorption of heavy metals by the mineral of tropical soils[J]. Appl Geochem,2003,18:795-804
[71]Gomes PC, Fontes MPS, SilvaAG, Mendoncal ES and Netto AR. Selectivity sequence and competitive adsorption of hesvy by Brazilian soils[J]. Soil Sci Soc Am J,2001,65:1115-1121.
[72]Serrano S, Garrido F, Gampbell CG, et al. Competitive sorption of cadmium and lead in acid soils of Central Spain[J]. Geoderma,2005,124(1-2):91-104
[73]Usman A R A. The relative adsorption selectivities of Pb, Cu, Zn, Cd and Ni by soils developed on shale in New Valley, Egypt[J]. Geoderma,2008,144(1-2):334-343
[74]McKeague J A, Day J H. Dithionite and oxalate extractable iron and aluminum as aids in differentiating various classes of soils [J]. Soil Sci.,1966,46:13-32
[75]徐明岗,李菊梅,张青.pH对黄棕壤重金属解吸特征的影响[J].生态环境,2004,13(3):312-315
[76]王新,梁仁禄,周启星.Cd-Pb复合污染在土壤-水稻系统中生态效应的研究[J].农村生态环境,2001,17(2):41-44
[77]郭观林,周启星,李秀颖.重金属污染土壤原位化学固定修复研究进展[J].应用生态学报.2005,16(10):1990-1996
[78]郭鹏,郭平,康春莉,等.城市土壤吸附重金属动力学特征及其与土壤理化性质的关系[J].环境保护科学,2008,34(6):23-26
[79]吴平霄,徐玉芬,朱能武,等.高岭土胡敏酸复合体对重金属离子吸附解吸实验研究[J].矿物岩石地球化学通报,2008,27(4):356-36
[80]Boekhold A E, Temminghoff E J M, Vanderzee S E AT M. Influence of electrolyte composition and pH on cadmium sorption by an acid sandy soil[J]. J Soil Sci.,1993,44:85-96
[81]Elliott HA, Denneny. Soil adsorption of cadmium from solution containing organic ligands [J]. J Environ Qual,1982,11(4):658-662
[82]Neal RH, Sposito G. Effects of soluble organic matter and sewage sludge amendments on Cd sorption by soils at low Ca concentrations[J]. Soil Sci,1986,142(3):164-172
[83]林大松,徐应明,孙国红,等.土壤pH、有机质和含水氧化物对镉、铅竞争吸附的影响.农业环境科学学报,2007,26(2):510-51
[84]Schnitzer M. Soil organic matter-The next 75 years[J]. Soil Science,1991,151:41-58
[85]白庆中,宋燕光,王晖.有机物对重金属在粘土中吸附行为的影响[J].环境科学,2000,21(5):64-67
[86]熊雄,李艳霞,韩杰,等.堆肥腐殖质的形成和变化及其对重金属有效性的影响[J].农业环 境科学学报,2008,27(6):2137-2142
[87]Brown S L, Chaney R L, Hallfrish J G, et al. In situ soil treatments to reduce the phyto - and bioavailablity of lead, zinc and cadmium[J]. Journal of Environment Quality,2004,33:522-531