Accumulations And Distributions Of PAHs, PCBs In Typical Crops

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants because of their high toxicity, persistence, and bioaccumulation. As the primary producers in the ecosystem, crops can accumulate of PAHs and PCBs which would enter into high-level consumers with the feeding of herbivores in the ecosystem. Humans' body can accumulate PAHs and PCBs by eating food directly which could pose a threat to human health. Therefore, the study of the distribution and accumulations of PAHs and PCBs in crops can enrich the basic theory of bioaccumulation, and provide a theoretical basis for environmental management and food security.In this study, the analysis method of PAHs and PCBs in crops was set up based on the review of related literature at home and abroad. Furthermore, the PAHs and PCBs concentrations and pollution sources in wheat and maize were analyzed and identified. Finally, the distributions, accumulation characteristics and toxicity of PAHs and PCBs in wheat and maize were explored separately. This dissertation included the following contents and conclusions:(1) A new analytical method was developed for the determination of PAHs and PCBs in plant samples. The extraction and purification procedures, accelerated solvent extraction (ASE) and gel permeation chromatography (GPC) cleanup were presented by optimizing different extraction conditions and the fraction collection time, respectively. The results showed that the method recovery percentages and relative standard deviations (RSD) were 82.00%～118.31% and 5.35%～17.76% for PCBs,69.83%～87.37% and 8.27%～18.49% for PAHs. The results meet the U.S.EPA standard of recoveries and RSD of repeated samples.(2) Wheat samples of 4 growth stages and corresponding rhizosphere soil and irrigation water samples were collected and analyzed. Soil and irrigation water contents of PAHs and PCBs in study area were at a low level. The concentrations of 16 PAHs in the various periods of wheat were 0.24～2.23μg/g dw.; PCB 138 and PCB 180 were not detected out in various periods of the wheat, and the concentration of all other PCBs seized 0.066-0.60ng/g dw.. Correlation analysis of PAHs and PCBs in wheats and those in the corresponding soils and water were carried out. The results show the concentrations of PAHs and PCBs in the wheats were not significantly related to those in the rhizosphere soils suggesting that the PCBs and PAHs in soils was not the source of wheat.(3) During the wheat growth process, PAHs and PCBs contents in the jointing stage wheat were largest and the decreasing trend enrichment factors of PAHs and PCBs in wheat verified this law. In Jointing and filling stages, PAHs and PCBs showed the same law:leaf> stem> root> ear. Different ring-number PAHs and chlorinated-number PCBs content did not show the consistent change in different tissues. In mature stage Wheat, logKow of PAHs affect the PAHs absorption. The low-ring PAHs were more likely to be absorbed than the high-ring PAHs by root. Finally, correlation analysis of PAHs and PCBs content and crude fat of different wheat tissues were carried out. The content of PAHs and PCBs in leaves and ears was significantly correlated with the crude fat content.(4) The PAHs and PCBs contents of maize rhizosphere soil were at a low level. All the 16 kinds of PAHs were detected out in the roots, stems and leaves of different periods maize, when only 11 kinds of PAHs were detected in seeds, and the concentrations of PAHs were 0.31- 1.65μg/g dw.; PCB 138, PCB153 and PCB 180 had a lower detection rate than other PCBs. PCBs contents of the tissues were 4.82-147.18 pg/g dw., and were lower than the PCBs contents in wheat.(5)During the maize growth process, the largest PAHs and PCBs contents appeared in the end of seedling stage. PAHs concentrations in the final ear and mature stage showed the same law:leaf> root> stem> seed. Different ring-number PAHs and chlorinated-number PCBs contents did not exhibit the same characteristics. The PAHs enrichment factors of maize were lower than those of wheat. The PAHs enrichment factors of maize were higher than PCBs, because of higher solubility of PAHs than PCBs. The logKow of PAHs had an opposite impact on the maturity of maize and wheat which showed the accumulation and uptake of PAHs was not only related to the nature of PAHs, but also related to the different researched species. Fat content in maize seed affected the content of PAHs and PCBs obviously.