Effect Of Colloid On Pb Transport And Biological Effect Of Pb

The exposed Pb in environment poses a critical threat to the humans'survival. This study focused on the solid Pb products weathering and transport in soil. Based on the summary of the results of previous research in related fields, historical data, laboratory simulation and field experiments, focused on the solid Pb products abration, Pb transport and Pb chemical forms in the ecosystem, this thesis studied the physical and chemical behavior of Pb in the environment, with sand soil, loessal soil and Brassica Chinensis.This thesis revealed the mechanism of colloids associated Pb transport in soil and porous media with different environment perturbation, pointed out the weathering rate of Pb in the nature environment, revealed the effect of Pb fraction on the enzyme in Brassica Chinensis and loassel soil, and ascertained the combination of Pb chemical form and enzyme as the Pb pollution assessment index.With the research of overall this thesis provided the scientific basis and practical guidance for Pb evaluation and management. The main conclusions obtained are as follows:(1) Soil moisture, organic matter content and soil pH significantly affected the weathering of lead, as a result, low soil moisture, low organic matter content and high pH conditions conducive to reducing the rate of lead weathering. The weathering rate of lead was lower than that in soil. Therefore, replacement the soil with sand was one of the best management to reduce the weathering of solid Pb products. For all solid lead products contaminated soil, the management methods are certainly feasible, which is important to the waste Pb products management.(2)Thesis revealed the colloid significantly promoted the migration of lead in huge intact soil cores, pointed out that the decrease of ionic strength and increase of flow rate significantly increased the lead and colloids transport in soil, but when the flow rate reached a certain limit, due to plugging and re-precipitation the colloids deposited, resulting the concentration of colloids and lead in the leachates reduced and stabilized. Thus, in a nature environment, the increase in intensity of rainfall or irrigation will lead to colloid facilitated lead as a contaminate moving down to the groundwater.(3) Revealed the important effect of properties of the soil on colloids and the lead leaching. In colloids and soluble organic matter riched alkaline sandy soil, the lead mainly leached out as dissolved Pb or combined with nano-sized colloids. In low organic matter content acid sandy soil, the lead out with coarse colloidal lead.(4) In the experiment simulating colloid and lead transport in saturated porous media, we found that static (instantaneous) and dynamic strong adsorption from Pb ions to sand occurred in the sand column. In the same experimental conditions in other cases, the colloidal particle size was the crucial factor effecting the colloid migration and deposition in saturated porous media. In the same experimental conditions (flow rate, porous media), colloid transport was significantly fast than lead migration. The sand column had higher retention to lead than its retention to colloid.(5) This thesis discussed the distribution of Pb chemical forms in the added polluted loessal soil. The concentration of all Pb fractions increased with the increasing of Pb in loessal soil, and all the Pb fractions maintained a balance within a variable range (<20%). The exchangeable Pb occupied a small part in loessal soil, the main fraction of Pb was carbonate bound Pb, organic matter bound Pb, residual Pb, which was not easily absorbed by plants, Pb fractions with high concentration was not the most harmful in somewhat. Tested soil contains much carbonate, which formed abundant carbonate Pb, while the abundant organic bound Pb was because of the strong adsorption and sequestration of organic matter. Oxides content in the soil is relatively low may be due to lower content of iron and manganese oxides or reaction conditions. This thesis disscussed the response of soil enzyme to the lead in added polluted loessal soil, which showed that the total lead had no any effect on the activity of three kinds of soil enzyme, further more ascertained the total lead content was not so good to evaluate the Pb pollution of loessal soil lead pollution.(6)Moreover catalase activity significantly increased and alkaline phosphatase activity significantly decreased with Pb increasing in loassel soil, which showed that they both can be the evaluation index of Pb pollution in loassel soil, but urease was not. The combination of peroxidase, alkaline phosphatase and carbonate bound Pb can be the Pb polution evaluation index because of the effect of carbonate bound Pb on the peroxidase and alkaline phosphatase was the most among all Pb fractions.(7) This thesis disscussed the effect of added Pb sources on the plant enzyme and Pb fraction in Brassica Chinensis. When the soil was polluted by Pb, the antioxidant capacity of peroxidase and polyphenol oxidase in Brassica Chinensis leaves was increased to protect the body from lead hazards.(8)The added lead significantly increased the concentration of all fractions Pb in Brassica Chinensis roots, and only acetic acid and hydrochloric acid extractable Pb in leaves. The main accumulation of Pb in leaves and roots was unactivated hydrochloric acid extractable Pb. Though the added Pb in soil changed the Pb fraction distribution patterns, all Pb fractions in Brassica Chinensis root kept a proper ratio after soil was polluted with Pb. All Pb fractions kept a certain percentage in Brassica Chinensis leaves no matter the soil was polluted with Pb or not. The exchangeable Pb in Brassica Chinensis leaves was increased in somewhat showed that the activity of Pb increased.