Studies On Health Risk Assessment And Reduction Techniques Of Cadmium In Tobacco

Cadmium is a toxic heavy metal which harms human health, and about 7% agricultural soils have already exceeded the National Standard for Environmental Quality in Cd contamination over recent decades in China. Also tobacco is a high accumulation plant for Cd, so Cd can be accumulated in human body by chronically smoking cigarettes. Therefore formulating criteria of health assessment and finding reduction measures of Cd in tobacco has been a hot topic in the fields of tobacco industry and public health. Firstly suggestions on criteria of Cd assessment in tobacco were provided with relevant references on health assessment method and tobacco smoking. Then effects of amendments, antitraspirants and zinc fertilizer on reducing Cd absorption in slight/moderate Cd-contaminated soils were evaluated though pot experiment and long-term field experiment with exogenous Cd added. The aims of this study are providing reference for health risk assessment of tobacco Cd and technical guidance for producing tobacco with low Cd concentration and slight/moderate Cd-contaminated soil remediation.1. The recommended formula to calculate cadmium limits of tobacco with assessment method of World Health Organization was provided, and 2 mg/kg, 5 mg/kg were estimated using each formula based on atmosphere cadmium limits or digestion cadmium limits. Besides, suggestions on Cd grading criteria of tobacco and soil were provided on the basis of Cd concentration distribution and Cd enrichment equation of tobacco leaves.2. Application of amendments significantly decreased soil available Cd concentrations, and annual variation of immobilization efficiency decreased firstly, then trend to stable at last. Immobilization efficiency of them was found to follow an order: RMRS, RMCS> RM, RS> CS, and RMRS was an efficient amendment because its immobilization efficiency was still nearly 30% after 4 years. The amendments can lower Cd concentration of root by 10.6%~19.5%, especially strong mobility patterns like ethanol and water extractable Cd. Also they decreased 20.0%~54.5% Cd in xylem saps. Cd content in tobacco plants of all treatments were found to follow an order, i.e. bottom leaf > middle leaf and upper leaf > stem. In addition, the concentrations of Cd in tobacco were most positively influenced by soil available Cd concentrations. The annual change of Cd content was the most apparent in bottom leaves and the least in other parts. With time went by, the difference in Cd concentration of upper, middle and bottom leaves was narrowing. Meanwhile, using amendments can increase the yield of tobacco leaves, the ratio of mid-high grade leaves and economic benefit. Application of zinc fertilizer decreased 25% Cd of xylem saps transfer into shoots, so it can much more significantly lower Cd concentration in different parts of tobacco plant. The antagonistic efficiency of zinc fertilizer declined slightly while keeping stable, which had been maintained at 15%~25% in these four seasons.3. The results of pot experiment studying on antitranspirants to reduce Cd absorption in tobacco showed that spraying our invented antitranspirant named as fulvic acid potassium and zinc(F-Zn) had no influence on biomass and physiological index of tobacco. It can decrease Cd accumulation in shoots by 20%, increase the concentration of K and Zn by 15.1% and 7.5 times, respectively. Interestingly, abscisic acid most significantly lowered cadmium content, yet it impeded dry matter accumulation, physiological metabolism and mineral nutrients accumulation such as K 、 Zn. The shoot Cd concentration was most positively related to transpiration rate, and root Cd concentration was negatively related. Undoubtedly, the results of field experiment were basically same as pot experiment. The Cd concentrations of middle and upper leaves were decreased by 11.8%, 9.1%, and the concentrations of K and Zn were raised by nearly 20% and 1-2 folds after spraying F-Zn on the leaf surface.4. The results of field experiment studying on antitranspirants combined with amendments to reduce Cd absorption in tobacco showed that both antitranspirants and amendments were significantly influenced on Cd absorption in tobacco. And the effect of antitranspirants was better than amendments in the late stage of tobacco. The effect of antitranspirants combined with amendments on reducing Cd absorption was better than single method. In conclusion, red mud and rape straw with zinc fertilizer and foliar application of F-Zn is most effective method among all treatments in this study to decrease Cd phytoavailability in soil-tobacco system.