| DDT, as a typical persistent organic pollutant, although has been forbidden so many years, still retains a high level in the environment and could transfer into organisms through the food chains. Crops in contaminated soil could take up and accumulate DDT whereas their normal growth and development would be affected. Global CO2 concentration keeps rising these years, and CO2 as the substrate of photosynthesis, its changing concentrations play an important role in crop growth and resistance. In order to improve agricultural product safety and to reduce DDT threat on human health, it is important to screen the vegetable varieties suitable for DDT polluted areas as well as study the growth and development, DDT uptake and accumulation in vegetables under elevated CO2. In this study, different varieties of common vegetables, such as mustard (Brassica juncea), Chinese mustard (Brassica rapa L. Chinensis Group.), Chinese cabbage(Brassica rapa pekinensis) were used to study the differences in DDT uptake and accumulation among different vegetable varieties; varieties grew well in DDT contaminated soil while with the least DDT were screened out. Then further research was conducted under elevated CO2 to study the growth, physiologic and biochemical responses, as well as DDT uptake and the risk assessment of the three vegetables screened out in the pre-experiment, by using Open top Chamber device (OTC) as well as the gas chromatography mass spectrometry (GC-MS) and other advanced detection means. The main results are summarized as follows:1. DDT stress response of different vegetable varieties was studied through soil pot culture. The results showed that genetic variation in tolerance and uptake of DDT existed among different vegetable varieties. The growth and yield of Chinese cabbage Qinggeng (B.cq) were slightly promoted, while inhibition in two other celery cabbage species (Chundawang, B.coc; Zaoshu NO.5, B.coz) as well as the Chinese cabbages Ziguan NO.1 (B.cz) and Suzhouqing (B.cs) were observed. There was almost no influence to the two mustard varieties (Brassica juncea var. foliosa Bailey, B.jf; Brassica juncea (Linnaeus) Czernajew var. multisecta L.H. Bailey, B.jm). Differences were detected in the obsorbing and transporting capacity of different varieties or genotypes vegetables. DDT concentration in shoot turned out to be:B.coz> B.cq> B.jm>B.cz> B.jf> B.bchg> B.coc> B.cs; while in root to be:B.jm> B.coc> B.jf> B.cz> B.cq> B.coz> B.cs> B.bchg.But overall, DDT accumulation in all the vegetables was not high. The degradation of soil DDT could be accelerated by planting vegetables and the DDT residues in soil after planting were as follows:B.jf<B.coz<B.cq<B.cs<B.cz<B.bchg <B.jm<B.coc. The effect of eight vegetables with DDTs on normal human health (non-carcinogenic) is tiny, but the potential risk of cancer to human body is a bit high. The lower-risk varieties in mustard, Chinese mustard and celery cabbage are B.jf, B.cs and B.coc, respectively.2. The biomass of Dayejingjie (B.jf), Suzhouqing (B.cs) and Chundawang (B. coc) was inhibited, while root volume, length, surface area, tip numbers were increased and then inhibited with the increasing concentration of DDT. Elevated CO2 eased the inhibition caused by DDT pollution, which was most obvious in B.jf. Furthermore, the promotion on the growth and biomass of vegetables growing in DDT contaminated soil, which was caused by elevated CO2 concentrations biomass, was related to the increasing chlorophyll levels and enhanced photosynthesis. MDA contents in B.jf as well as B. coc were reduced under increased CO2 concentration/DDT pollution condition, while no change of SOD activity was detected in the three vegetables.3. As CO2 concentration rises, the shoots and the roots of vegetables responded differently with various DDT concentrations. When the soil was treated with low concentration DDT (0.5 mg kg -1), elevated CO2 concentration put little effect on the DDT contents in roots of these three vegetables. Whereas, DDT content in shoots showed the following changes:B.jf was decreased by 15%, B. cs was reduced by 28% while B. coc was increased by 12%. When the soil was treated with high concentration DDT (5 mg kg -1), DDT concentrations in the aboveground and underground part were increased under elevated CO2:71%,15.3% and 14% respectively for the aboveground part of B. jf, B. cs and B. coc; 72%,23% and 26% for the underground part, respectively. In 2.5 mg kg-1DDT treated soil, DDT concentrations in the aboveground part of B.jf was increased only 2% under the elevated CO2 concentration, while the underground part to be 58%. DDT concentrations in shoot and root of B. cs was-14% and 25% respectively, while the changes in B. coc turned out to be 36% and 8%.4. As the concentration of DDT increases, the average daily exposure(ADE), the hazard ratio(HR) for non-cancer and cancer would increase accrordingly when eating DDT-contained vegetables, regardless of ambient and elevated CO2. The ADE, as well as HRcancer increased under elevated CO2, especially at high DDT concentration (5mg kg-1), under which the highest growth up to 125% appears on B. jf while the minimum growth only 15% in B. coc.The above results indicated that DDT uptake by vegetables was very low, and mainly in roots. Under elevated CO2 level, the biomass, the net photosynthetic rate (Pn) and DDT uptake of B.jf, B.cs and B.coc were increased, while ADE and HR were also enhanced. The plant water use efficiency (WUE) and chlorophyll content were changed, the root growth was also promoted;the biomass and DDT accumulation of plant increased, which would play a very important role in improving the phytoremediation efficiency of soil organic pollutants such as DDT as well as the development of phytoremediation technology. But on the other hand, elevated CO2 increased the consumption risk of vegetables growing in DDT contaminated soil, which means that elevated CO2 may affect the food security under the global climate change in the future. |
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