【作者】 崔立强；

【导师】 潘根兴； 李恋卿；

【作者基本信息】 南京农业大学 ， 土壤学， 2011， 博士

【摘要】 Cd/Pb是对人类健康具有极大威胁的重金属元素,随着土壤-作物-食物的食物链迁移,农田Cd/Pb污染已日益显现为我国环境健康的突出问题。我国南方是稻米的主要产区,该地区土壤重金属污染日益扩张,大多土壤偏酸,稻米重金属吸收和积累存在着重要的食品安全风险。因此,重金属污染稻田稻米安全生产的有效修复措施成为大家研究的热点。修复措施主要包括工程修复、物理化学修复以及植物修复等方面。工程修复具有效果彻底、稳定等优点,但实施复杂、治理费用高和易引起土壤肥力降低等缺点；物理化学修复,见效快,但有的改良剂可能会带来二次污染,并且还有活化的风险；植物修复费用低,可清除污染物,但是生物量小,修复时间较长。因此为了实现降低重金属的作物吸收,提高粮食安全,寻找一种改善和提高土壤质量,降低重金属的有效性的经济有效措施和技术显得尤为重要。生物黑炭是生物质原料在中低温(350-500℃)热裂解过程产生的一种低密度炭化物质。它具有很高的稳定性、很大的比表面、大量的表面负电荷和高的电子密度,同时,其pH值高,吸附和固定重金属能力强,从而具有修复土壤重金属的潜力。因此通过施用生物黑炭,达到改善土壤环境、缓解并治理土壤污染、同时,提高土壤碳库,减缓气候变化的目的。从探讨生物黑炭对重金属的吸附解吸能力出发,试验分析生物黑炭钝化农田重金属而降低作物吸收的效果,讨论其作用机制,以期为发展生物黑炭产业和农田环境治理技术提供科学依据。主要结果如下：1.在室内进行了生物黑炭在Cd浓度序列,时间序列,溶液初始pH值序列,不同粒径大小以及用量的吸附解吸试验。在生物黑炭对不同浓度Cd的等温吸附试验中,生物黑炭对溶液中Cd2+的吸附效率达到98%以上,随着Cd溶液浓度的升高生物黑炭的单位吸附量呈增加的趋势。吸附效率同吸附量成反比,即随着吸附量的增加吸附效率呈下降趋势,但是吸附效率下降的速率远低于吸附量增加速度。生物黑炭对溶液中Cd的吸附仅需10多分钟即达到平衡。生物黑炭对Cd的吸附量随溶液的pH值升高而增加,并且生物黑炭固液比对溶液pH值也有明显影响,吸附达到平衡时,溶液pH值相对于初始值提高了10.4%-73.9%。生物黑炭吸附能力随粒径减小而增大,当粒径小于0.84 mm时,单位吸附量增加幅度变小；当粒径小于0.84 mm时,吸附量增加幅度变小；而粒径大于0.84 mm时,单位生物黑炭吸附量会大幅度减少,降幅度达21.8%。随着生物黑炭使用量的增加,单位吸附量逐渐减少,而吸附效率逐渐增大；当生物黑炭用量在8 g L-1,吸附效率可达90%以上。生物黑炭吸附Cd的解吸效率在1.83%-5.39%间,用量越大,单位重量的生物黑炭解吸量越小,解吸率越低。这表明Cd与生物黑炭产生了结合固定。通过生物黑炭与污染土壤的竞争吸附试验,表明污染土壤中Cd相对于Pb在生物黑炭的竞争吸附中占据优势,这可能与Pb在土壤中的化学活性较低有关。2.采用田间试验验证分析了生物黑炭对污染土壤的Cd/Pb钝化和降低作物吸收的效果。选择苏南某地重污染农田,2009年水稻播种前施用了0,10,20,40 t ha-1的生物黑炭,在2009-2010年水稻和小麦收获时采集作物样品和土壤样品,分析表明,施用生物黑炭显著提高了土壤pH值,与对照相比提高了0.16-0.38单位。施用不同量生物黑炭显著降低了水稻季CaCl2浸提态Cd显著降低了32.0%-52.5%(2009),39.8%-43.4%(2010),CaCl2浸提态Pb两年内没有显著变化；DTPA浸提态Cd/Pb与对照相比2009年没有显著差异,但2010年显著降低了21.6%-48.6%和11.9%-20.3%；小麦季土壤中Cd含量也得到显著的降低,与对照相比,CaCl2和DTPA浸提态Cd分别下降了23.4%-40.1%和11.1%-12.0%；但对CaCl2浸提态Pb含量无显著影响,不过生物黑炭显著降低了麦季土壤中DTPA浸提态Pb含量(15.0%-18.8%)。施用生物黑炭对水稻和小麦的产量没有显著影响,保持稳产,但显著降低了稻麦籽粒中Cd含量,水稻糙米Cd含量与对照相比降低了16.8-45.0%(2009年)和39.9%-61.9%(2010年),而小麦籽粒中Cd含量与对照相比降低了24.8%-44.2%(2010年)；对Pb含量几乎没有影响。同时,水稻和小麦各组织中Cd的含量随生物黑炭施用量的增加也有着不同程度的降低。对比单位农田面积籽粒吸收Cd的数量可以看出,每公顷稻米的Cd吸收量与对照相比减少了45.8%-64.5%(2009年)和39.8%-64.5%(2010年),而小麦则减少了32.1%-42.3%(2010年)。从以上的试验结果来看,本试验效果与要优于相邻试验田施用钙镁磷肥和氢氧化钙的效果。施用生物黑炭处理下,作物组织Cd富集系数降低了39.8%-66.1%(水稻)和29.0%-49.6%(小麦),Cd地上部转移系数降低了15.9%-38.5%(水稻)和5.9%-36.6%(小麦)；说明生物黑炭处理下抑制作物根系对Cd的吸收以及Cd的向上转运,是降低籽粒Cd积累的重要途径。上述研究证明,生物黑炭钝化土壤Cd活性的作用显著,并且此效果至少可持续两年,但对Pb无显著影响。3.选择中度污染重金属稻田,研究生物黑炭用于农产品安全生产的可行性。于2010年选取重金属中度污染稻田,设置了0,10,20,40 t ha-1四个用量梯度,探讨污染稻田生物黑炭修复和稻米安全生产可行性。中度污染土壤的pH为5.36,土壤CaCl2和DTPA浸提态Cd达0.55 mg kg-1和2.72 mg kg-1,水稻糙米Cd含量达到0.72mg kg-1。施用不同用量生物黑炭显著提高土壤pH值(0.65-1.08个单位)。同时,CaCl2浸提态Cd显著降低了(48.0%-70.9%),土壤有效态Pb也降低了17.0%-34.0%,而DTPA浸提态Cd和Pb没有显著变化。生物黑炭的施用对水稻产量无显著影响,但糙米中Cd含量下降了18.8%-43.3%,Pb含量下降了13.7%-38.1%。施用生物黑炭之后水稻不同组织的Cd/Pb含量也有着不同程度的降低。糙米Cd含量降低到0.41 mg kg-1,基本达到CCFAC (Codex Committee on Food Additives and Contaminants)规定的农产品安全限值标准0.4 mg kg-1。同时,在成熟期水稻Cd富集系数降低了66.2%-78.3%之间；而拔节期和灌浆期降低了41.0%-76.8%之间；同时还观察到Pb的富集系数在各个时期显著降低,幅度在17.4%-64.1%之间。成熟期,灌浆期和拔节期Cd转移系数变化趋势基本一致,生物黑炭处理下降低了23.9%-47.3%之间,不过Pb的转移系数没有显著变化。4.污染土壤施用生物黑炭后,土壤有效态Cd/Pb与pH呈显著相关关系,由此可见,生物黑炭的施用引起的土壤pH的升高是导致土壤Cd/Pb有效性降低的重要影响因素。同时,连续两年的土壤有效态Cd/Pb和籽粒Cd/Pb含量结果比较显示,随着生物黑炭施用年限的延长,黑炭对土壤重金属的固持作用增强,进一步降低土壤Cd的有效性,明显抑制了水稻籽粒中Cd的富集。综上所述,无论在重度污染还是中度污染农田,生物黑炭的施用均能显著降低土壤中重金属的有效性,减少农作物对重金属的吸收；试验结果表明生物黑炭的改良修复效应至少可以持续两年。生物黑炭钝化土壤重金属、降低作物重金属吸收量的机制在于,其巨大的比表面可以大量、快速地吸附和固持土壤中重金属,并由于其较强的碱性,降低重金属的化学移动性而达到钝化重金属的效果,从而抑制了土壤-作物系统的迁移和籽粒积累,大大降低了稻麦籽粒中Cd/Pb的含量,提高了重金属食物安全性。更多还原

【Abstract】 Cd and Pb are two of heavy metals that is a great threat to human health with migrating in the soil-plant-food chain, and farmland Cd and Pb pollution has become the outstanding problem of environmental health. In South China, the rice production areas of heavy metal contaminated become serious with most of the acid soil, which is posing potential public health risk for human and food safety. So, it becomes hot research that heavy metal pollution effective repair measures in paddy rice for safe production. Restoration measures include engineering repair, of physical chemistry repair, phytoremediation and so on. Though the effects engineering repair were complete, stable, etc., the defects of it were complex process, high cost and decreased soil fertility etc.; Physical chemistry repair were quickly and could produce food with repair processing, but some amendments maybe bring secondary pollution, and exist risk of activation; Phytoremediation were low cost, clean remove contaminants, but the biomass of plant was small and needed a long repair time. So it was necessary to find a cost-effective methods and technologies, in order to reduce the heavy metal uptake by plants and improve food security.Biochar produced by that the biomass (Such as:wood, crop residues, nut shell, coconut shell, bark, wastepaper etc.) is heated to moderate temperatures, between about 350 and 500℃(giving the process the name "low-temperature pyrolysis"), under complete or partial exclusion of oxygen. It is one of the low density low-temperature pyrolysis material and a new soil amendment. There are such characteristics:high stability, corrosion resistance, and greater ability retain fertilizer compared with other forms of organic fertilizer. What is more, the biochar could increase the soil pH to hold the soil nutrition elements and heavy metals because of the large surface area and surface negative electric charge. So the biochar could be used to mitigate climate change, improve the soil environment, relieve the environmental pollution and have the potential for pollution control. In order to explore the biochar adsorption characters and stabilization mechanism to the heavy metals, we design lab experiments and field experiments to analyze adsorption and desorption capacity of the biochar and the effect immobility the heavy metals to reduce the crop uptake. We hope that it can provide a scientific basis for biochar industry and farmland pollution environmental control technology. The main results just as follows:1. The lab experiments include the biochar adsorption and desorption under Cd concentration sequence, time sequence, initial pH sequence, different partial sizes and dosage. The biochar adsorption efficiency reached over 98% in Cd solution, and adsorption amount unit increased with the Cd concentration increase in the biochar adsorption isotherm under different Cd concentration. It is inverse proportion that the biochar adsorption efficiency and adsorption amount, namely the adsorption amount increased and the adsorption efficiency decreased, but adsorption amount increased rate faster than adsorption efficiency decreased rate. The biochar adsorption rate was fast and reached equilibrium in 10 min. The biochar removal efficiency increased with pH increasing for Cd, and great effect on the Cd solution after adsorption reached equilibrium and the solution pH increased by 10.4%-73.9% compared to initial pH.The smaller partial size, the larger adsorption ability of the biochar. When the partial size was smaller than 0.84 mm, the increase rate decreased of the adsorption amount. When the biochar partial size was larger than 0.84 mm, the biochar adsorption amount unit decreased by 21.8% sharply. The adsorption amount unit decreased and adsorption rate increased with biochar amount increasing. When the biochar concentration was at 8 g L-1, adsorption rate reached over 90%.The biochar desorption rate was between 1.83% and 5.39%, with the biochar amount increasing, desorption amount unit and desorption rate decreasing. It was indicated that the Cd is very strong to combined biochar, not easy to desorption. So it was more likely the specific adsorption of the biochar. The biochar adsorbed much more Cd than Pb in contaminated soil with the biochar application.2. A field experiment was set to test the effect of biochar on passivating soil Cd/Pb and reducing crop Cd/Pb uptake. The amounts of 0,10,20,40 tone biochar per hectare were supplied in the seriously polluted paddy soil before rice planting in 2009. The results of analyzing the soil and plant samples in 2009 and 2010 were that, biochar application improved the soil pH by 0.16-0.38 units.After the biochar application in rice season, the CaCl2 extraction soil available Cd were decreased by 32.5%-52.5% (2009) and 21.6%-48.6%(2010), but no significant difference of soil available Pb in two years. The DTPA extraction soil available Cd and Pb were decreased by 21.6%-48.6% and 11.9%-20.3% only in 2010. Compared to control treatment, the available Cd/Pb contents in wheat season soil were decreased by 23.4%-40.1% (CaCl2 extraction Cd), 11.1%-12.0%(DTPA extraction Cd) and 15.0%-18.8% (DTPA extraction Pb) under biochar applications.Although there was no significant effect of biochar on crop yield, rice and wheat grain Cd contents was significantly decreased by 16.8-45.0% (rice grain in 2009),39.9%-61.9% (rice grain in 2010) and 24.8%-44.2% (wheat grain in 2010), and the grain Pb contents were not changed. Meanwhile, different rice/wheat tissues Cd contents were significantly decreased under biochar application. Compared the Cd uptake in grain per hectare among different treatments, Cd grain uptake per hectare were significantly decreased by 45.8%-64.5% (rice grain in 2009),39.8%-64.5% (rice grain in 2010) and 32.1%-42.3% (wheat grain in 2010) under biochar application. And the effects of biochar are better than calcium-magnesia phosphate fertilizer experiment in the aside field.Under biochar application, Cd accumulation coefficients were significantly decreased by 39.8%-66.1% (rice) and 29.0%-49.6%(wheat), and Cd transfer coefficients were also significantly decreased by 15.9%-38.5% (rice) and 5.9%-36.6% (wheat). It indicated that inhibiting the Cd absorption from root and transfer to grain were both key ways to reduce the grain Cd contents with biochar application.The study above showed that the passivating of biochar on available Cd in contaminated soil was significant, and the effect of biochar on soil pH and soil available Cd can last at least two years.3. The experiment was carried out on moderately polluted cropland to study the feasibility of biochar application on the safe food production of agriculture.The four biochar supply grads (0,10,20,40 t ha-1) were set to probe the feasibility of biochar application on the safe food production of agriculture. In moderately polluted field, the pH was 5.36, and the DTPA and CaCl2 extraction Cd were 0.55 mg kg-1 and 2.72 mg kg-1, respectively; the brown rice Cd content was up to 0.72 mg kg-1. After the application of biochar, the soil pH were increased by 0.65-1.08 units, and the CaCl2 extraction Cd/Pb were both decreased by 48.0%-70.9% and 17.0%-34.0%, respectively; but there were no significant difference in DTPA extraction Cd/Pb among the treatments. The rice yield was not significantly changed with biochar application, but the brown rice Cd/Pb contents were decreased by 18.8%-43.3% and 13.7%-38.1%, respectively. Moreover, the plant tissues Cd/Pb contents of rice were also significantly decreased. The rice grain Cd content was decreased to 0.41 mg kg-1, which was close to the limit value of CCFAC (Codex Committee on Food Additives and Contaminants). Meanwhile, both of Cd and Pb accumulation coefficients were reduced in different periods; The Cd accumulation coefficients was significantly 66.2%-78.3% in Ripen stage, and 41.0%-76.8% in Filling stage and Jointing stage; The Pb accumulation coefficients was between 17.4% and 64.1% in whole growth stage. The Cd transfer coefficients between 23.9% and 47.3% in whole growth stage with biochar application.The results of field experiments on seriously polluted and moderately polluted croplands showed that, the application of biochar reduced the contents of soil available Cd significantly, and the available Pb contents were also reduced in moderately polluted cropland duo to its low pH. The effects of biochar on yield were not significantly, however, the Cd contents in grain and plant tissue in two experimental fields and the Pb contents in the crops in moderately polluted field were all reduced under biochar application. Through analyzing the accumulation coefficient and transfer coefficient, it was drawn that the biochar can inhibit the transfer of heavy metals from root to grain. Moreover, the Cd/Pb contents of crop grain planted on moderately polluted field did not exceed the limit value of CCFAC.4. There was significant correlation between the soil available Cd/Pb concentrations and pH values with the application of biochar in contaminated soils, which indicated that the increasing of soil pH may be the most important factor on heavy metals availability. Furthermore, long effort of biochar on the immobilization of the heavy metals in contaminated soils was found from the results of available Cd/Pb and Cd/Pb content grain in two consecutive years, and the Cd/Pb uptake and transfer process was then decreased.To sum up, both in the seriously and moderately polluted cropland, the application of biochar can significantly reduce the availability of heavy metals in the soil and the absorption in crops; moreover, the two years experimental results showed that the effect of biochar stabilized Cd/Pb at least last two years. The mechanisms of stabilization soil heavy metal and crop uptake reduction with biochar application were that the biochar has huge surface area which is benefit for absorbing and immobilizing numerous heavy metals in soil rapidly, and also its strong alkaline can increase soil pH to reduce the chemical mobility of heavy metals. Thereby, the biochar effects inhibited the migration of heavy metals in soil-plant system and reduced rice grain Cd/Pb uptake greatly, so as to improve the food security.更多还原