Analysis Of Pb Sources And Influencing Factors In Radish Produced In Urumqi

Vegetables are an essential ingredient in people’s daily lives,and most of the vegetable production areas are concentrated in the suburbs of towns and cities,which are vulnerable to a variety of heavy metal pollution sources.The content of Pb in soil background in Urumqi is low,but the phenomenon of Pb exceeding the standard in some vegetables still occurs from time to time.In this paper,the root vegetable radish was taken as the research object,and the pollution sources and influencing factors of Pb in Urumqi local radish were discussed by isotope tracer method,combined with the L₁₆（4⁵）pot orthogonal experiment and fertilizer"3414"experiment design,which provided theoretical basis for Pb pollution prevention and safe production in vegetables.（1）The contribution rates of dustfall,soil and irrigation water to the Pb content in above-ground of radish were 31.29%,67.61%and 1.32%,respectively,and the soil had the greatest influence on the accumulation of Pb in the above-ground of radish.the contribution rates to the Pb content in the roots of radish were 72.46%,18.66%and 9.30%,respectively,the dustfall had the greatest influence on the accumulation of Pb content in radish roots.The ratios of Pb isotopic characteristics in the above-ground and roots of radish were close to those of flue gas ash,urea,phosphorus fertilizer,sludge and other plants（okra leaves,pearl plum leaves,willow leaves）,which indicating that Pb in radish was most susceptible to these environmental media,and the Pb pollution of radish planted in the open conditions had homology with other plants.（2）The root Pb content of radish grown under open conditions ranged from 0.115 to 0.174 mg·kg^-1,at a distance of 10m away from the highway behind the Agricultural Building of Xinjiang Agricultural University,which all exceeded the National Food Safety Standards-Limits of Contaminants in Food（GB2762-2017）(Pb≤0.1 mg·kg^-1),and the exceeding rate was 100%.The radish leaves absorbed a certain amount of HCO₃^-,SO₄^2-,Mg²⁺,K⁺,Na⁺and Pb from dustfall,while Ca²⁺and Cl^-were released.The Pb content in above-ground of radish was mainly affected by HCO₃^-,Ca²⁺and Pb in the dustfall,the Pb content in roots was mainly affected by SO₄^2-and Pb in the dustfall,and the wet dustfall had a great influence on the Pb content in roots.（3）The effect of soil salt ions on Pb content in above-ground of radish was as follows:Pb²⁺>Na⁺>Ca²⁺>Mg²⁺>K⁺,the order of influence on root Pb content was Pb²⁺>Na⁺>Mg²⁺>Ca²⁺>K⁺.Pb content in aboveground part of radish was significantly positively correlated with Pb²⁺content in soil,and significantly negatively correlated with Na⁺,the content of Pb in roots was less affected by soil salt ions,only positively correlated with Pb²⁺in soil and close to the significant level（r=0.938,P=0.062）.The Pb content（fresh weight）in above-ground of radish was not detected to 0.125 mg·kg^-1,the Pb content（fresh weight）in roots was ranged from 0.003 to 0.150 mg·kg^-1,and the exceeding rate in roots was 12.5%.（4）The effect of salt ions in irrigation water on Pb content in above-ground of radish was as follows:Ca²⁺>Pb²⁺>Mg²⁺>Na⁺>K⁺.The Pb content in above-ground of radish was not detected to 0.094 mg·kg^-1（dry weight）,the Pb content in the roots was not detected to 0.084 mg·kg^-1（dry weight）,and that in the roots did not exceed the standard.The cations in irrigation water in Urumqi had little effect on Pb accumulation in radish.（5）The application of nitrogen and phosphate fertilizer could increase the leaf length,root length,stem diameter,above-ground and root fresh weight of radish under medium level Pb(100 mg·kg^-1)stress.The application of nitrogen fertilizer had no significant effect on the absorption of Pb by radish roots,but the phosphate fertilizer could inhibit the absorption of Pb by radish roots.Based on the relationship between crop yield and quality and safety production,the optimal application rates of nitrogen fertilizer（N）and phosphate fertilizer（P₂O₅）in radish planting were 287.29 mg·kg^-1 and 154.49 mg·kg^-1,respectively.On the basis of medium-level nitrogen(300 mg·kg^-1)and phosphate(150 mg·kg^-1)fertilizer application rates,with the increase of Pb concentration,the absorption of Pb by radish roots gradually increased and the difference was significant（P<0.05）,while there was no significant effect on the absorption of Pb in aboveground parts.