Contamination And Cumulative Effect Of Heavy Metal In Peri-urban Vegetable Soils In Typical Cities Of Jilin Province

Due to rapid industrialization and urbanization, contamination of urban soils ison an increase all over China. The quality of urban agricultural land is closely relatedwith the health of the population. The suburb is the main producing area ofagricultural products, and vegetable production in peri-urban areas is now a key sectorof the urban agricultural economy, therefore, the environmental quality of peri-urbanvegetable fields should be paid more attention to all over the world. Among allchemical contaminates, heavy metals are considered potential hazardous contaminantsin the biosphere to human health. This kind of pollution exhibits the followingcharacteristics: wide range, long time with toxicity, invisibility, easily cumulating,transfer along with food chain and hardly resuming etc. The study on the spatialdistribution characteristics and risks of heavy metals in peri-urban vegetable soils is ofgreat significance to soil environment quality and safety in vegetable production.Using peri-urban vegetable plots in four typical cities (Changchun, Jilin, Siping andSongyuan) in Jilin province, the research carried out field survey, lab analysis and potexperiment. The distribution and cumulative effect of heavy metals in peri-urbanvegetable soils are researched systematically. Then the environmental quality ofvegetable fields was classified as four classes based on the soil environmentalstandard, and we thoroughly studied the accumulation rules of heavy metals underdifferent environmental condition and planting patterns. At last, on the basis of theresearch results, we can guide the safe production of vegetables in study area. Themain results of this study are as follows:1. The pollution and spatial distributions of heavy metals in the peri-urban vegetable soils in the major cities of Jilin province were made clear. Due to thedifference of the intensity of the human activities and regional differences, theenvironmental quality of vegetable fields in the cities varied greatly. The heavy metalcontents in most of the peri-urban vegetable fields in Changchun, Jilin, Siping andSongyuan exceeded their background values of Jilin province, some exceeded thenational first standard and little reached to the national secondary standard, and Cdwas the major element. The distribution of heavy metals was constrained by bothnatural and contrived factors, and hotspots were mainly distributed in industryconcentrating area and downwind area of prevailing wind.2. To identify the potential sources of heavy metals in peri-urban vegetable soils.With Changchun and Jilin, for example, the multivariate statistical analysis resultssuggested that Pb, Cu and Zn were consistently from anthropogenic sources, while Crand Ni were from natural sources with low concentrations.3. To estimate the metal availability in peri-urban vegetable soils. WithChangchun city, for example, the results showed that available metal concentrationsshowed large variability and the CV values exceeded those of the total metal forms. Itis clear that though the total metal concentrations are not perceived to be particularlyhigh, the availability of Pb, Cr, Cu, Ni and Zn may present a relatively high level andincrease risk of these metals to accumulate to microbial and plant tissues.4. To evaluate the environmental quality of peri-urban vegetable fields. Singlegene index method and complex pollution indices method were used in this paper toevaluate the environmental quality of peri-urban vegetable fields in Changchun, Jilin,Siping and Songyuan. The environmental quality of most vegetable fields was atguard line and light pollution level, and little fields reached heavily pollution grade.Cr and Ni had relatively low levels of contamination and were less influenced byhumanity. Pb, Cu, Zn and Cd were relatively seriously influenced by anthropogenicactivities, especially for Cd. Spatial distribution of synthetic pollution index inperi-urban vegetable soils indicated that the heavy metal pollution indifferent citiesvaried greatly from regional differences.5. The environmental quality of vegetable fields in Changchun, Jilin, Siping and Songyuan was classified as four classes based on the soil environmental standard.Most of the vegetable fields in study area were non-pollution vegetable productionbases, some fields could be used as organic and green vegetables bases, and few fieldsrequired risk assessment before being used to grow vegetables, but all of the vegetablefields could be used to grow vegetables.6. To study the cumulative effect of Pb in Chinese chives under different cuttingfrequency through pot experiment. Lead concentrations in Chinese chives roots werefirst decreasing and then increasing with the increase of cutting frequency over aperiod of time, and extremely low values occurred under cutting twice. Leadconcentrations in Chinese chives stems were increasing with the increase of cuttingfrequency, Pb concentrations in stems had slight decline when cutting five timesunder high Pb pollution. Lead content in Chinese chives leaves were first increasingand then decreasing with the increase of cutting frequency, and extremely high valuesoccurred under cutting three and four times. The concentration and content of Pb inleaves had not risen with the increase of growth time continued to falter, indicatingthat the Pb in Chinese chives leaves was not stationary and had a continued movementwithin the plant.7. To study the cumulative effect of Pb and Cd in spinach under alone stress andcombined stress through pot experiment. Pb and Cd showed anti-action when the Cdconcentrations in soils were0.35and1.4mg/kg, respectively, indicating that Cd waslimiting Pb absorption. Pb and Cd showed synergy when the Cd concentrations insoils were4.9mg/kg, indicating that Cd was promoting the uptake of Pb by spinach.Pb and Cd showed adding effect when the Pb concentrations in soils were75mg/kg.Pb was limiting Cd absorption when the Pb concentrations in soils were300mg/kg.Pb and Cd showed obvious anti-action when the Pb concentrations in soils were1050mg/kg, indicating that Pb was limiting Cd absorption by spinach.8. To study the cumulative effect of Cd in spinach and pakchoi under singleplanting system and through pot experiment. Pakchoi did not make significantdifference under different planting ways, but pakchoi showed different accumulativerules. The content of Cd in pakchoi under companion planting system was significantly higher than single planting system, indicating that pakchoi waspromoting the uptake of Cd by spinach under companion planting system. Thephenomenon was likely due to that pakchoi root exudates and Cd formed chelate forbetter uptake by spinach, and spinach and pakchoi formed a competition undercompanion planting system, and then promoted the produce of spinach root exudates.The exudates could activate heavy metals by dissolving, chelation and reduction toincrease the accumulation of Cd by spinach, so spinach and pakchoi were unsuitablefor companion planting, and the capacity of accumulating Cd for spinach was strongerthan pakchoi.