腐殖酸活性组分含量和比例对紫色潮土中铅的形态转化及生物有效性的影响

发布时间：2018-01-12 19:05

本文关键词：腐殖酸活性组分含量和比例对紫色潮土中铅的形态转化及生物有效性的影响　出处：《西南大学》2017年硕士论文　论文类型：学位论文

【摘要】：铅是对人体健康危害较大的重金属元素,尤其对儿童的身体发育和神经系统影响显著。土壤铅的环境危害作用不仅与其总铅含量有关,更大程度上取决于其在土壤中的赋存形态及分布状况。腐殖酸广泛分布于自然环境中,因其复杂的结构和较高的反应活性而在影响土壤重金属形态与生物活性的众多因素中扮演着特殊而又十分重要的角色,施用含腐殖酸类物质的有机物料常作为土壤重金属污染修复措施之一,但有机物料(如腐殖酸、有机肥等)中活性组分组成因其物料来源、腐熟化条件的不同而异,施用含腐殖质物质等有机物料对土壤重金属的活性调控效果常不一致。有机物料组成复杂,其对重金属活性的影响方向和程度是其各种组分综合作用的结果。腐殖酸是有机物料的主要活性组分,包括胡敏酸(HA)和富里酸(FA),两者均可与土壤重金属发生络合(螯合)作用,但高分子量的胡敏酸在土壤中移动性差,与土壤矿物结合紧密,而FA等低分子组分则能保持较高的移动性和生物活性,因此,两者在有机物料中含量和比例可能是决定其最终效应的重要原因。同时,污染土壤中的铅可通过直接暴露对人群健康产生危害,而降低土壤中重金属植物有效性的措施,能否同时降低人体直接接触土壤的健康风险还有待考究。为此,本研究通过室内模拟实验,探讨腐殖酸的两大活性组分含量和比例对铅在土壤中的吸附解吸特性、形态转化和化学可提取性的影响,并结合体外胃肠模拟试验方法研究测定不同腐殖酸状态土壤中铅的生物有效性,阐明不同种类和比例的腐殖酸影响下土壤铅生物有效性与其吸附解吸和形态转化之间的关系,为深入了解腐殖酸环境化学行为及利用含腐殖酸有机物料修复土壤铅污染提供科学依据。主要研究结果如下:腐殖酸(HAs)对土壤铅的吸附解吸特性的影响受其种类、含量和比例的制约。HA能有效促进土壤铅的吸附,显著增加土壤铅的平衡吸附量和吸附速率常数,而FA和HA/FA为5/5的HAs则显著降低了土壤铅的吸附能力,平衡吸附量未达到对照(CK)的50%,土壤铅吸附速率常数较CK分别降低了18.92%、29.12%。供试土壤对铅具有强力吸附能力,添加外源铅浓度最高为1500mg·L-1时,CK及HA处理土壤还未达到饱和吸附,而FA及HA/FA为5/5的HAs处理土壤铅均达吸附平衡状态,最大吸附量分布在21.44~36.52 mg·g-1,且随着FA含量或HA/FA比值的增加,土壤铅的吸附能力均有所提升。铅在所有腐殖酸处理后的紫色潮土中的解吸率均不超过15%,但与CK相比,HA处理土壤所吸附的铅难以解吸,而FA处理土壤则降低了铅的吸附强度,解吸率较CK增加了1.60~14.12个百分点。在等量HAs(1%C)条件下,当HA/FA≥7/3时HAs能降低铅的解吸率,而当HA/FA≤5/5时HAs对土壤铅的解吸能力显著增加,促进了土壤铅的解吸,增加了土壤铅释放的环境风险。不同活性组分含量及比例的腐殖酸对土壤铅形态分配的作用方向和影响程度差异较大。外源铅进入土壤后,随培养时间的延长,添加HA的土壤交换态铅的降低速率高于FA。转化达平衡后,HA添加量为0.5%C、1%C、3%C、5%C的土壤碳酸盐结合态铅百分含量较CK分别降低了5.79、9.95、15.79、20.37个百分点,不同FA添加量的土壤交换态和碳酸盐结合态铅百分含量较CK分别增加了3.31~17.01和0.07~10.03个百分点。在相同HAs(1%C)用量水平下,HAs对于土壤铅的钝化或活化作用受HA/FA比的制约,当HA/FA比≥7/3时,土壤有效态铅含量均低于CK,而当HA/FA比≤5/5时,其对铅的表观效应与FA相似,增加了土壤铅的有效性。HA主要通过促进碳酸盐结合态铅向铁锰氧化态、有机结合态和残渣态铅的转化而对土壤中铅具有钝化作用,FA则通过降低铁锰氧化态、有机结合态和残渣态铅的分配比例,大幅增加交换态和碳酸盐结合态铅的分配比例而活化土壤中的铅,且他们的钝化或活化作用随着HAs用量的增加而逐渐增强。HAs对土壤铅化学提取有效性的影响与铅的赋存形态具有密切联系,回归分析表明,紫色潮土化学可提取态有效铅含量以交换态铅和碳酸盐结合态铅对其贡献最大。通过铅的抑制或活化百分率可知,HA对土壤铅的钝化作用与其用量呈显著正相关关系:y1=5.12 x+8.31(P0.05,n=4);FA对土壤铅的活化作用存在临界点,当FA用量≥1%C时,土壤铅活化百分率急剧增加10.01%,出现明显上升拐点,土壤铅的生物有效性和毒性显著增加。不同HAs处理土壤的铅在胃阶段的生物可给性均远远高于肠阶段的生物可给性,而HAs不同活性组分含量及比例对铅的生物可给性的影响较大。PBET方法中,不同碳含量HA处理土壤铅在胃肠阶段的生物可给性均低于CK,降幅分别为0.36%~1.54%、0.99%~3.85%,而不同FA碳含量影响下的土壤铅在胃阶段的生物可给性较CK明显增加,且增幅为2.20%~6.02%,当FA≥1%C时的土壤铅在肠阶段的生物可给性显著增加,较CK增加了5.01%~12.87%,且胃肠阶段的生物可给性均与FA碳含量呈正相关关系。在等量HAs(1%C)条件下,当HA/FA≥7/3时铅在胃肠阶段的生物可给性均低于CK,HA/FA≤5/5时均高于CK。SBET方法中,HA均降低了铅的生物可给性,降低幅度与HA添加量呈正相关关系,FA均增加了铅的生物可给性,当FA≥1%C时增幅更加明显。HAs对土壤铅的生物可给性与铅的赋存形态呈显著相关性(P0.01),PBET(y1)和SBET(y2)两种方法在胃阶段的铅生物可给性受交换态(x1)、碳酸盐结合态(x2)、铁锰氧化态(x3)和有机结合态铅(x4)的影响,关系式分别为y1=-7.827+0.968x1+1.001x2+0.574x3+0.764x4(R2=0.996),y2=-1.439+1.287x1+1.046x2+0.656x3+1.160x4(R2=0.994);而铅在肠阶段的生物可给性主要受交换态和碳酸盐结合态两种形态铅调控(R2=0.904)。因此在选取有机肥等有机物料治理土壤铅污染时应考虑采用HA或HA组分占比较高的修复材料,以降低土壤活性态铅的含量,有效抑制土壤铅对植物或人体的毒害作用,而采用化学提取态判定铅在人体内部生物有效性时需考虑胃部强酸性的情况。
[Abstract]:Lead is a heavy metal, the harm to human health, especially the effect on the physical development and the nervous system of children. Significant environmental hazards of soil lead to not only the total lead content, to a large extent depends on the speciation in soil and distribution. Humic acid is widely distributed in the natural environment, because of the reaction the complex structure and high activity and the main influence factors of soil heavy metals and biological activity plays a special and important role in the application of organic materials containing humic acids used as one of the heavy metal contaminated soil remediation measures, but the organic materials (such as humic acid, organic fertilizer and so on) in the active component. Because of its material sources, different curing condition of rot, activity regulation effect of humic substances containing organic materials in the soil heavy metals are often inconsistent. Organic materials. The complex, its influence on the activity of heavy metal in the direction and extent of its various components. The comprehensive effect of humic acid is the main active group of organic materials, including Hu Min acid (HA) and fulvic acid (FA), both with the soil heavy metal complex (chelate), but humic acid with high molecular weight in the soil poor mobility, combined with soil minerals, FA and low molecular components can maintain mobility and high biological activity, therefore, both in the content of organic materials and the proportion may be an important cause of its final decision effect. At the same time, the pollution of lead in soil by direct exposure to cause harm to people health, and reduce the availability of heavy metal in the soil plant measures can also reduce health risks in direct contact with the human body soil remains to be determined. Therefore, this research through laboratory simulation experiment, humic acid of two active components The content and proportion of adsorption and desorption characteristics of Pb in soil, chemical speciation and extractable effects, combined with the determination of bioavailability of lead in soil of different humic acid condition in vitro gastrointestinal simulation test method, the relationship between the effect of humic acid to clarify the different types and proportion of the soil lead bioavailability and adsorption desorption and transformation, to understand the environmental chemical behavior of humic acid and provide scientific basis for the utilization of humic acid containing organic materials to repair the soil lead pollution. The main results are as follows: humic acid (HAs) effect on adsorption and desorption of lead in soil by their types, restricting the content and proportion of.HA can effectively promote the adsorption of Pb in soil the significant increase in adsorption capacity and adsorption rate constants of lead in soil, while FA and HA/FA 5/5 HAs significantly reduced the adsorption capacity of lead in soil, the equilibrium adsorption amount has not reached Control (CK) 50%, soil Pb adsorption rate constant CK decreased 18.92%, 29.12%. soil has strong adsorption ability of Pb, Pb added the highest concentration of 1500mg, L-1, CK and HA in soil has not yet reached the saturation adsorption, while the FA and HA/FA 5/5 HAs of soil lead as the adsorption equilibrium, the maximum adsorption capacity distribution in 21.44~36.52 mg g-1, and with the increase of FA content or HA/FA ratio, soil Pb adsorption capacity increased. Desorption of lead in all humic acid treated in purple soil were less than 15%, but compared with the CK, HA adsorption in soils the lead desorption, and FA soil decreased the adsorption strength of lead, the desorption rate increased by 1.60~14.12 percentage points higher than CK. In the same amount of HAs (1%C) conditions, when HA/FA is larger than 7/3 HAs can reduce the lead desorption rate, desorption capacity when HA/FA = 5/5 HAs on soil lead Increased significantly, promote the desorption of lead in soil, increase the environmental risk of soil Pb release. Different active component content and the ratio of humic acid on soil Pb speciation distribution influence direction and degree of difference. Pb in soil, with prolonged incubation time, add HA of soil exchangeable lead reduce the conversion rate is higher than the FA. reached equilibrium after HA was added to 0.5%C, 1%C, 3%C, 5%C soil carbonate bound Pb content compared with CK were decreased by 5.79,9.95,15.79,20.37 percentage points, different FA contents of soil exchangeable and carbonate bound Pb content of CK were increased 3.31~17.01 and 0.07~10.03 percentage points HAs (1%C). At the same dosage level, HAs for passivation of lead in soil or activation by HA/FA than the control, when the HA/FA ratio is greater than or equal to 7/3, the lead content of soil is lower than that of CK, while HA/ FA is less than 5/5, the To lead the apparent effect similar to FA,.HA increase the effectiveness of lead in soil mainly through promoting carbonates lead to iron and manganese oxides, conversion of organic bound and residual lead and passivation effect of lead in soil by reducing FA, Fe Mn oxide, organic bound and distribution proportion the residual lead, a substantial increase in the exchangeable and carbonate distribution proportion of Pb and Pb in soil activation, and their activation or inactivation increased with the amount of HAs increased.HAs on lead extraction chemical soil influencing the validity and lead deposit form has close connection with the regression analysis showed that the purple soil chemical extractable Pb content in effective exchangeable Pb and carbonate bound Pb. The greatest contribution to lead through inhibition or activation of the percentage, HA passivation effect on soil Pb and its amount was positive shut off Department: y1=5.12 x+8.31 (P0.05, n=4); the role of FA on the activation of soil lead the existence of critical point, when the content of FA is not less than 1%C, the percentage of activated soil lead a sharp increase in 10.01%, significantly increased the inflection point, the bioavailability and toxicity of lead in soil increased significantly. HAs treatment in different biological soil lead in the stomach of the to the stage are far higher than the intestinal bioavailability, and HAs of different active component content and the ratio of the bioaccessibility of Pb is greatly influenced by the.PBET method, different carbon content in the HA soil lead in the GI phase bioaccessibility were lower than CK, the reduction rate of 0.36%~1.54% and 0.99%~3.85%, respectively. The biological effects of different carbon content of Pb in soil FA under the stage to stomach than CK increased significantly, and the increase of 2.20%~6.02%, when the biological soil lead FA is not less than 1%C in the intestinal phase availability increased significantly, increased by 5.01%~12.87% compared with CK, and gastrointestinal stage Bioaccessibility and FA carbon content were positively correlated. In the same amount of HAs (1%C) conditions, when HA/FA is not less than 7/3 in the stage of gastrointestinal lead bioaccessibility were lower than that of CK method was higher than that of CK.SBET HA/FA is less than or equal to 5/5, HA decreased the bioaccessibility of Pb, and decreased the amount of HA was positively correlated, FA increased the bioaccessibility of Pb, when FA is not less than 1%C was more obvious in.HAs on soil lead bioavailability and speciation of Pb was significantly correlated (P0.01), PBET (Y1) and SBET (Y2) lead bio two methods in gastric stage the availability of exchangeable, carbonate bound (x1) (x2), Fe Mn oxide (x3) and organic bound Pb (x4) effect relationship were y1=-7.827+0.968x1+1.001x2+0.574x3+0.764x4 (R2=0.996), y2=-1.439+1.287x1+1.046x2+0.656x3+1.160x4 (R2=0.994); and the biological lead in the intestinal phase is mainly affected by the availability of exchangeable And carbonate bound two forms of lead control (R2=0.904). So in the selection of organic fertilizer and other organic material treatment of lead contaminated soil should be considered when using HA or HA components for repair materials relatively high, in order to reduce the content of soil active Pb, effectively inhibit soil Pb toxicity to plants or human body, and the judge should consider the state chemical extraction lead strong acid in the stomach inside the human body bioavailability.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53

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