Varietal Differences In Cadmium Absorption By Brassica Rapa And The Effect Of Exogenous Zinc And Manganese On Cadmium Accumulation In Vegetables

With the development of economy and society,continuous emissions of industrial waste gas,waste water,and massive automobile exhaust emissions have led to contamination of heavy metals,especially cadmium in agriculture soils.Vegetables are an essential part of people's daily diet.They may also have a high ability for cadmium absorption.Cadmium can enter the food chain and then enter the human body via the vegetable intake,causing a risk to human health.Therefore,cadmium accumulation in vegetables poses a threat to the safety of agricultural products,affecting agricultural sustainable development.How to take effective measures to reduce cadmium absorption and the threat to human health becomes a very important issue.Zinc and manganese are essential trace elements to human body.Zinc and cadmium are in the same group in the Periodic Table,both having similar chemical properties.Some studies have shown that the addition of soluble Zn can decrease cadmium absorption by plants.Therefore,we conducted hydroponic,pot,and field experiments to study the differences of cadmium absorption capacity among different kinds of vegetables and the effect of exogenous zinc and manganese on cadmium absorption in vegetables.The main results are summarized as follows:In the hydroponic experiment,cadmium uptake of ten varieties of brassica rapa was compared.Results showed that in the prensence of 0.5 ?mol/L cadmium in the nutrient solution,the cadmium absorption capacity by the roots of Gaojiaoshigengbai,Chiifu,CGN15199 was significantly higher than that of other varieties,while cadmium translocation from roots to shoots in Jinlu75,Daqingmaye,L58DH was significantly higher than other varieties.A pot experiment was conducted to study the effect of exogenous zinc and manganese on cadmium absorption in Chinese cabbage.Result showed that compared with the control,cadmium concentration in cabbage with 1 mg·kg^-1 cadmium treatment added to the soil was significantly higher.Cadmium concentration in Chinese cabbage with 10 mg·kg^-1 zinc treatment was significantly lower than other groups.Manganese treatments showed no significant effect on cadmium concentration in Chinese cabbage.Results showed that exogenous zinc can significantly improve available zinc in the soil,and reduce cadmium absorption in Chinese cabbage.A vegetable field in the suburban of Tianjin with cadmium contamination risk was chosen to study the effect of exogenous zinc and manganese on cadmium absorption in vegetables.Results showed that cadmium content in the soil was lower than the soil environment quality standards,and the concentrations of cadmium,arsenic,lead and chromium in vegetables also met the standards of pollutants for national standards of food safety.Three methods were used to estimate the contribution of atmospheric deposition and soil dust to the contents of heavy metals in vegetables.For cadmium,arsenic,lead and chromium,the median contribution from atmospheric deposition and soil dust was 33.7%?83.7%?72.8%and 71.0%,respectively.It is clear that arsenic,lead and chromium in vegetables in the experimental area mainly came from the atmospheric deposition and soil dust.Washing can effectively reduce heavy metal content in vegetables.