| Charcoal, an important type of black carbon, which is produced from incomplete combustion of vegetation and fossil fuel is ubiquitous in terrestrial and aquatic environments, it have been reported to be as high as up to 45% of the total organic matter in soils and sediments. In addition to its important role in the global carbon cycles and effects on the Earth's radiative heat balance, black carbon in soil may also potentially contribute to the sorption and sequestration of organic contaminants, and thus effectively influence the environmental process (mobility, degradation, toxity, bioavailability, and bioremediation) of those contaminants in soils. In this thersis, we produced two kinds of charcoals pyrolysised under different temperatures, the fast sorption/desorption and slow sorption/desorption behavior of pesticides in soil amended with charcoals were determinded, together with the influence on pesticide degradation in soil and plant uptake of pesticide from soil when charcoal were amended. The objective of this study was to assess the effect of the presence of small amounts of charcoal materials in soil on the sequestration and thus the bioavailability of pesticides in soil. The main results are as following.1. Charcoal preparation and character determination. Synthetic charcoals were produced through carbonization of red gum (Eucalyptus spp.) wood chips at 450 oC and 850 oC (refer to as charcoal BC450 and BC850 in this paper), respectively. The specific surface area (SSA) of two charcoals was evaluated by BET nitrogen adsorption technique at 77K, using automated manometric gas adsorption apparatus and ultra high purity gaseous nitrogen. The pore volume and micropore size distribution was evaluated with Horvath-Kawazoe (H-K) method. Result showed that the SSA for BC850 was 566.39 m2·g-1, which was much higher than that of charcoal BC450 (27.33 m2·g-1). Results of pore size distribution analysis showed that charcoal BC450 had a very low level of microporosity (peak maxima occurred at a pore width of about 1.1 nm), while BC850 was predominantly a microporous material with about 89.6% of volume from micropores (peak maxima occurred at a pore width of about 0.45 nm).2. Sorption/desorption behavior of diuron on real soil. Tthe sorption and desorption behavior of diuron on 3 natrual soils were tested. The results showed that the sorption capacity was closely correlated with the content of total organic carbon in the natural soil, and the extent of sorption isotherm nonlinearity depended on the relative contents of organic carbon and black carbon in the soil. However, the sorption desorption hysteresis was correlated with the black carbon content in soil. The calculated index of hystersis (H value) was 1.42,1.61, and 1.88 for soil ss6, ss8, and ss7, with the content of black carbon in soil was 0.07%, 0.819%, and 2.145%, respectively.3. Impact of charcoal on the fast sorption/desorption behavior of pesticides. With pesticides diuron and pyrimethanil as models, we tested the fast sorption and desorption (24h) behaviors of the pesticides on soil amended with different levels of the two charcoals, by means of batch equilibrium technique and successive dilution techniques, respectively. The results showed that the sorption capacities, sorption isotherm nonlinearty and apparent sorption-desorption hysteresis markedly increased with increasing content of charcoals in the soil, and more prominantly in case of charcoal BC850, presumably due to the presence of micropores and it's relatively higher specific surface area. Comparison of the results for the two types of charcoal materials also revealed that although the sorption capacity of a soil could be enhanced to the same level (e.g. compare 0.8% BC850 versus 5% BC450 on sorption of diuron), but the degree of reversibility was quite different between the two charcoals. This may due to the microporouse charactore of charcoal BC850, and the main cause of sorption-desorption hysteresis was"pore conditioning"by contaminants. Through analysising the relationship between the sorption-desorption hysteresis index (H) and the pore volume (V) of sorbents (calculated from the Vt optoarle value and content of charcoal material in the soil), we found that the degree of sorption-desorption hystersis showed a good correlation with the micropore-volume of the charcoal amended soils. The hysteresis index"H"increased exponentially (H=1.582 e0.008x, R2=0.8982, for diuron, and H=1.7113 e 0 .0098v, R2=0.9135 for pyrimethanil) as the total pore volume of the sorbent increased.4. Impact of charcoal on slow sorption/desorption behavior of pesticides. To demonstrate the effects of charcoals on slow sorption and its influence on desorption of pesticides in soil, impact of sorption contact time on the sorption and desorption behavior of diuron on soils amended with different amount of charcoal was determined. Results of the sorption determination showed that the sorption capacity of the soils newly amended with charcoal increased with the rate of charcoal amended increasing. Longer contacting time could increase the amount of pesticide sorbed by soil, and the slow sorption fraction of diuron was related to the content of charcoal in soil. The result of desorption experiment showed that there were clearly increase of the anti-desorbable fraction of diuron with the increased sorption contact time and content of black carbon in soils. When diuron was sorbed by soil amended with 1.0% black carbon for 56 days, the desorption rate was less than 2%.This study indicates that presence of small amounts of charcoal in soil could have a marked effect on the release behavior of organic compounds. Mechanisms of this apparent hysteretic behavior need to be further investigated, as well as its impact on the bioavailability of pesticides in soiols5. Impact of charcoal on the degradation of pesticide in soil. Impact of the two charcoal samples on the degradation of pesticide chlorpyrifos in soils was evaluated, together with the influence on the amount of microorganism in soil. The results showed that charcoal in soil could stimulate the growth of bacteria and fungi in soil. Degradation rate of chlorpyrifos in soil was mainly caused by microorganism, the half life of chlorpyrifos in unsterilized original soil was 24.7 d, while in sterilized soil, and the half life was 165 d. The half life of chlorpyrifos in soil amended with 0.1%, 0.5%, and 1.0% BC450 were 31.6, 33.5, and 47.5d, respectively; and were 31.5, 37.5, and 71.5d in soils when amended with BC850 at the level of 0.1%, 0.5%, and 1.0%, respectively. The results demonstrated that charcoal could markedly delay the degradation of pesticide in soil, and charcoal produced under higher tempreture (eg. BC850) has more prominantly effects, which was closely correlated with its relatively higher sorption capacity against pesticides.6. Impact of charcoal on the uptake of pesticides by plant from soil. By amending a sandy soil with different levels of charcoal BC450 and BC850, uptake of two pesticides (carbofuran and chlorpyrifos) with different water solubility fortified in the soils by Spring Onion (Allium cepa) were measure after cultivated for 35 days, respectively, as well as the pesticides degradation rate in soils and the plant biomass. The results are as following. 1) Charcoal in soil could incent the growth of the plant, and the two pesticides also could affect effects on the growth of the plant. Plants cultivated in soils with higher content of charcoal have higher fresh weight than in those with lower or zero content of charcoal, and charcoal developed under higher temperature have more prominent effects. The average fresh weight of spring onion were 10.98, 0.792, and 0.620 g per plant, respectiviely for plant that cultivated in soil amended with charcoal BC850, charcoal BC450, and original soil.The pesticide carbofuran fortified in soils could also incent plant growth. 2) Both the disappearance of carbofuran and chlorpyrifos in soil amended with charcoal were slower than that without charcoal amendement. Plant could incent the degradation of pesticides in soil. 3) Charcoal in soil could alleviate the uptake rate of pesticides by plant, and charcoal BC850 had more prominent effect than that of BC450, when amended in soil at the same levels. When Plant cultivated in soil without charcoal amendements, the amount of chlorpyrifos in the under- and up-ground part of spring onion were 0.094 and 14.120 mg·kg-1, respectively, and the amount of carbofuran were 0.160 and 14.44 mg·kg-1, respectively. When plant cultivated in the soils amended with charcoal at the levels of 0.1%BC450, 0.5%BC450, 1.0%BC450, 0.1%BC850, 0.5%BC850, and 1.0%BC850, in the up-ground part of spring onion, the amount of chlorpyrefos were 0.055, 0.048, 0.067, 0.060, 0.050, and 0.038 mg·kg-1, and the amount of carbofuran were 0.15, 0.11, 0.073, 0.11, 0.063, and 0.075 mg·kg-1. The results showed that pesticde with higher water solibility were seemed to be more easly took up by plants from soil. In the under-ground part of spring onion, the amount of chlorpyrefos were 14.15, 83.17, 6.81, 8.68, 3.53, and 0.80 mg·kg-1, and the amount of carbofuran were 12.75, 13.51, 7.88, 11.59, 4.11, and 1.77 mg·kg-1. Compare the amount of the two pesticides residues in under- and up-ground part of plant showed that carbofuran was seems to be more easily to be transported in the plant, as the difference of two pesticide residue in up-ground part of plants was more prominent than those in under-ground part.
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