Study On Pollution Status And Control Of Leafy Vegetables In Typical Heavy Metal Polluted Areas Of Yunnan Province

In recent years,the escalation of human activities has resulted in a significant increase in heavy metal pollution in soil.This pollution poses a serious threat to crop growth and can cause varying degrees of heavy metal contamination in crops.Leafy vegetables,which are a vital source of nutrients such as vitamins,dietary fiber,and other important minerals,are particularly vulnerable to heavy metal pollution in the soil.The excessive amount of heavy metal in leafy vegetables surpasses safety standards,leading to serious health risks when consumed for extended periods.Therefore,it is crucial to conduct research on leafy vegetables grown in heavy metal-contaminated areas to address the associated health concerns.This paper initiated a series of studies on the contamination of leafy vegetables in two heavily polluted areas in Yunnan Province.The primary focus of the research was on the tendency of leafy vegetables to accumulate higher concentrations of harmful heavy metals than other vegetable types.The three main studies carried out in this investigation are outlined below:（1）To investigate the heavy metal contamination of leafy vegetables in two heavily polluted areas of Yunnan Province,a total of 108 samples of 14 types of leafy vegetables and corresponding soil were collected from villages near the mining areas of Datun Town,Gejiu City,and Kuangshan Town,Huize County.The study aimed to detect the levels of Pb,Cd,As,and Cu in the soil and edible/non-edible parts of the leafy vegetables.Additionally,the corresponding heavy metal limits specified in the"National Standards for Food Safety Limit of Pollutants in Food"（GB2762-2022）and"Soil environmental quality-risk control standard for soil contamination of agricultural land（Trial）"（GB15618-2018）were compared,and an analysis of the degree of exceeding the standard for different heavy metals in leafy vegetables and soil was conducted.The bioaccumulation and transfer factors of leafy vegetables were calculated,and cluster analysis was performed to identify leafy vegetables with high and low accumulation of heavy metals.（2）After identifying the leafy vegetables with low accumulation of heavy metals,this study selected Malabar spinach（Gynura cusimbua）and eight locally planted varieties for further investigation.Using the method of indoor pot planting,the absorption of Pb,Cd,As,and Cu by different varieties of Malabar spinach was measured to identify those with low accumulation of heavy metals.Subsequently,the low-absorption varieties were planted indoors,and the heavy metal content of Malabar spinach was measured.Using linear regression,the study predicted the heavy metal threshold for safe planting of Malabar spinach.（3）To address the issue of high-accumulation leafy vegetables,Amaranth（Amaranthus tricolor）was selected for further investigation.The study adopted the pot passivation method using three different passivation agents:hydrated lime（SH）,zeolite（FS）,and rice husk biochar（DK）at various doses（0%,0.5%,1%,3%,and 5%）to passivate soil Pb and Cd by single application.The study then identified the passivation agent and dose that produced the best comprehensive effect for Pb and Cd passivation in Amaranth.Additionally,the study evaluated the effects of the passivating agent on the basic physical and chemical properties of soil and enzyme activities.Finally,the study investigated whether Amaranth could reach the safe edible standard after passivation.The main research results are outlined below:1.The contents of heavy metal in 108 leaf vegetable samples and corresponding soil in two study areas was determined.The results showed that the contents of Pb and Cd in soil in the two areas exceeded the corresponding screening values of soil pollution risk in agricultural land.In leafy vegetables,the main pollution elements are Pb and Cd,and Cu in leafy vegetables in both regions does not exceed the national limit.In the Kuangshan Town,the excess rates of Pb,Cd and As in leafy vegetables were84.62%,53.85%and 15.38%,respectively;The excess rates of Pb,Cd and As in leafy vegetables in Datun Town were 96.30%,37.04%and 25.93%,respectively.By calculating the hazard quotient（HQ）and hazard index（HI）,the results showed that the HQ values of Pb and Cd in some leafy vegetables were more than 1,while the HQ values of As and Cu in all samples were less than 1;For adults,the HI value of all vegetables except Malabar spinach is greater than 1,indicating that prolonged consumption of these leafy vegetables poses adverse health risks,and the health risks are more serious for children than adults.By calculating the bioenrichment and transport factors,it was found that malabar spinach is the only vegetable that does not accumulate four heavy metals.Therefore,Malabar spinach was selected as the leaf vegetable with low heavy metal accumulation,and Amaranth was selected as the leaf vegetable with high heavy metal accumulation due to its high bioaccumulation and transfer factors.2.The Malabar spinach pot experiment results showed that only some varieties Cd content exceeded China’s maximum permissible standards.Furthermore,Malabar spinach varieties A（instant Malabar spinach）,C（extra-large leaf green vine Malabar spinach）,and F（large leaf Malabar spinach）displayed the lowest Cd accumulation,which was not easy to accumulate Cd and could be selectively planted.Secondly,the linear regression of Cd content in soil and malabar spinach shows that when the total amount of Cd in soil and Cd total and bioavailable soil safety thresholds of 4.75 and0.77 mg·kg-1,respectively.The Cd content in auricularia will be at a high risk of exceeding the standard.3.In situ passivation experiments on high accumulation leafy vegetables showed that compared to FS and DK,SH had the best passivation effect,especially 5%SH,which significantly reduced available Pb and Cd in soil by 51.49%and 43.90%,respectively,but significantly increased p H by more than 10.Secondly,3%SH and 1%SH reduced the effective Pb and Cd contents to 25.85%,31.17%and 24.79,29.25%,respectively,and there was no significant difference between the two effects.Therefore,it is comprehensively considered to select 1%SH to passivate amaranth.Applying 1%SH had no significant effect on total nitrogen,total phosphorus,total potassium,available nitrogen,organic matter,and sucrase in soil,but it significantly increased available potassium in soil,and also significantly decreased the content of available phosphorus and urease in soil;It can reduce the content of Pb and Cd in the edible part of amaranth to within the safety standard.In conclusion,Pb and Cd were the main pollutants in 108 leaf vegetables samples and corresponding soil in the two study areas,and the HI value of most leaf vegetables was greater than 1,indicating that there was a risk to human health.Malabar spinach was selected as leaf vegetables with low accumulation of heavy metals,and varieties A,C and F were selected as low accumulation varieties.The proposed soil safety thresholds of total Cd and bioavailability were 4.75 and 0.77mg·kg^-1,respectively.The content of Pb and Cd in the soil was decreased by 1%SH,and the content of Pb and Cd in the soil was decreased by 1%SH,and the activity of available phosphorus and urease in the soil was decreased significantly,and the available potassium in the soil was increased significantly.