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Pot Experiment Study On Contaminated Behavioral Of Cd Under The Influence Of Coexistent Heawmetals In Arid Oasis Soil-Vegetabie System

Posted on:2011-12-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z J ZhaoFull Text:PDF
GTID:1101360305466009Subject:Environmental Science
Abstract/Summary:PDF Full Text Request
Among pollutants in agricultural soil, safety issues of agro-products caused by heavy metal pollutants have attracted high attention from all walks of life in the world. Long term sewage irrigation, fertilizer use, and piled-up industrial solid waste are the primary reasons for metallic elements'accumulation in surface layer of agricultural soil. Hexi Corridor is the most developed area on oasis farming in arid region of China. In this area, development of secondary industry, which gives priority to nonferrous metallurgy and chemical industry, plays a greatly improving role in local economy increase, but such development also has a distinctly adverse impact on environment. In the originally water-short conditions, sewage irrigation is used widely in locality, along with slathering of pesticide and fertilizer, thus, making heavy metal pollutants remain in bodies of animals and plants, and living environment, as poses severe threats to human health.Researches on heavy metal behaviors of chemical pollution in soil-vegetable system were started late in Hexi Corridor, leaving empty on studies of systematic experiments and multi-element pollution. Pot experiment, for which coles, celeries and carrots are experimental materials and the four heavy metals, Cd, Pb, Zn, and Ni, are the baseline, is conducted in oasis soil of arid regions. By the experiment, the paper explores behavioral expressions of pollution chemistry of soil and vegetables effected by Pb, Zn, Ni while coexisting with Cd; finds out the special habitats'effect on the single and combined contamination of these four elements; figures out vegetables'absorption and accumulation features to Cd and other coexistent elements. With statistical analysis, the paper builds a relation model between amounts and forms of soil heavy metals and vegetable absorption, offering theory supports to setting up basic database of heavy metals'transference and conversion in soil-vegetable system of arid districts, improving environmental quality of oasis soil, dominating heavy metal pollutions on vegetables, building green-vegetable production base, and guaranteeing qualities of agricultural products safety. The primary results are as follows:1) In oasis soil without contamination, coles, celeries and carrots were planted. Then, Cd in the soil mainly existed in Fe-Mn oxides fractions, while the proportion of exchangeable fractions was quite small. Soluble Cd added into soil, we found that exchangeable fractions response most strongly to concentration stress and residual forms response most weakly to such stress in the three-vegetable soil, demonstrating vegetables from growth to maturity conduct little fixed actions to Cd in the concentration range of experiment and that most Cd in relatively active patterns participates in various transferences in soil-vegetable system. Among the five patterns, carbonates fraction was the primary one while Cd was under diversified stresses. 2)In Cd pollution soil with Pb, Zn and Ni added, appearance and distribute regulation of Cd accords with the one in single action. These three elements'effects on Cd were as follows:Pb improved Cd activity in cole and carrot soil while restraining the one in celery soil; Zn acted completely opposite to Pb; Ni decreased Cd activity in cole and celery soil while increasing the one in carrot soil. Via the three kinds of combination, the comparative result of activity of Cd and other adding elements was Cd>Pb, Cd>Zn, Cd>Ni.3)Among the three-vegetable soil, exchangeable, carbonates, Fe-Mn oxides and organic matter fractions of Cd had notable correlations with stress degree under single Cd stress. Most of relative variation equations were linear model, more-than-1 power model in the second place. As to the Cd pollution soil with Pb, Zn, Ni added:Pb added, Cd of exchangeable, carbonates, and Fe-Mn oxides fractions in the three soil and Cd of organic matter fractions in cole soil had notable correlations with the stress degree. Each form changes in linear and more than 1 power model patterns, excepted that Cd of carbonates fractions in carrot soil varies in level-log model; Zn added, Cd of exchangeable, carbonates, Fe-Mn oxides and organic matter fractions in soil has significant connection with the stress degree. When it comes to fractions-stress model, fitted equations of Cd in different forms were linear, excepted that those of Cd of exchangeable and organic matter fractions in cole soil and Cd of Fe-Mn oxides fractions in celery soil were more than 1 power model, sigmoid curve and logarithm model in turn; Ni added, Cd in all forms, except for residual fractions, was closely related to stress degree. Most variation of Cd in each form is consistent with linear model, level-log and less than 1 power models in the next place.4)Under single Cd stress, when Cd concentration was low, inhibiting effect was primarily reflected on weight of each vegetable portion and length of aboveground parts; when Cd concentration was high (Cd≥4.9mg/kg), inhibiting effect on length of underground parts was rather distinct. The rank order of these three vegetables'tolerance level to Cd stress was cole>carrot>celery. The distribution regularity of accumulation amounts in each portioin of cole and carrot was aboveground parts>underground parts, while celery was right adverse. The rank order of Cd accumulation amounts in each portion of the three vegetables was cole>celery>carrot. There is obvious enrichment to Cd in every portion of cole and underground parts of celery. The main site that impeded Cd transference in cole was the migration boundary up and below the ground and the one that impeded Cd transference in celery was the migration boundary between soil and underground parts. Carrots did not enrich Cd much, and the capabilities in Cd enrichment of each migration boundary were fair. The ability in Cd enrichment of the three vegetables was cole>celery>carrots, and the one in transference was cole>carrot>celery.5)The three vegetables were planted in Cd contaminated soil with Pb, Zn and Ni added. The results indicated that when in high concentration (Pb≥450mg/kg), Pb could weaken Cd inhibiting effects on biomass of the three vegetables, that Zn could weaken Cd inhibiting effects on aboveground length of celery and carrot and when in high concentration (Zn>500mg/kg), Zn could also weaken Cd inhibiting effects on fresh weight of celery underground portions and carrot aboveground parts, and that Ni could weaken Cd inhibiting effects on length and fresh weight of celery aboveground portions and when in high concentration(Ni≥600mg/kg), Ni can also soften Cd inhibiting effects on fresh weight of celery and carrot aboveground portions and length of carrot aboveground parts.6)The three intervening elements did not change distribution rule in vegetables, but led to significant variations of accumulation amounts and capabilities in enrichment and transference what vegetables responsed to Cd. These variations were due to actions of intervening elements. Effects of Pb, Zn and Ni on Cd accumulation in the three vegetables might present antagonistic or synergistic as results of differences in concentration, species and portions of vegetables. Comparing accumulation and transference coefficients of Cd, Pb, Zn and Ni in homogeneous vegetables, we concluded Cd was the most feasible element that accumulates and transfers in vegetables, Zn in the next place, and that Ni and Pb were relatively less feasible.7)Effects of amounts of exogenous Cd on its accumulation in each portion of vegetables could be described by linear, less-than-1 power and logarithm models. The last two models pointed out self-protection of vegetables (cole aboveground parts and every portion of celery) against exoteric concentration interference. The variation equation of Cd transference in vegetables demonstrates that regular patterns of Cd transference in cole and celery were consistent with less-than-1 power model, while in carrot, the model was linear, as was possibly one reason why cole and celery are more tolerant to Cd. Under Cd pollution stress with Pb, Zn and Ni added, the variations of Cd accumulation in vegetables could still be described by linear, power and logarithm models, but in power models, the power was more than 1 (Cd and Pb compounded, Cd was accumulated in each portion of celery and underground parts of carrot; Cd and Zn compounded, Cd was accumulated in underground parts of cole; Cd and Ni compounded, Cd was accumulated in aboveground parts of celery and underground parts of carrot). All of these showed that the higher stress concentration in compounded actions, the larger increment of Cd accumulation in relevant portions of these vegetables. Cd and the other three concomitant heavy metals, live migration in vegetables could be imitated by linear, level-log and power models. The powers in all power models come near 1, the level-log models are suitable for compounded Cd and Zn, and Cd compounded with Ni transfers in carrot.
Keywords/Search Tags:Cd, Concomitant heavy metals, Soil-vegetable system, Arid region, Oasis, Pot experiment
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