Distribution And Ecological Risk Of Heavy Metals In Soils And Vegetables In Typical Vegetable Plots In Tianjin

Taking the soil of facilities in Wuqing District of Tianjin as an example,the spatial-temporal distribution characteristics,soil environmental quality and health risk of the soil in the facility were analyzed.The effect of soil physical and chemical properties on the change of heavy metal content was analyzed,and the content and health risk level of heavy metals in soil of facilities were evaluated.The heavy metal content of plough layer soil in the study area was Zn>Cu>As>Cd.The average content of the four heavy metals was lower than the national standard,which was in line with the requirements for soil quality of planting vegetables.However,the content of some samples of Cd exceeded the upper limit of the national facility soil regulations.The analysis of the spatio-temporal changes of heavy metals showed.As the soil depth of the facility increases,the heavy metal content has a downward trend.Cu,Zn and Cd in the 20-60cm soil layer showed a significant decline,indicating that heavy metals accumulate in the soil plough layer,of which Cd accumulation is most obvious.In the 0-10cm and 10-20cm soil layers,Cu,Zn,and Cd contents in addition to As varied greatly between different planting years,and Cu,Zn,and Cd contents increased in 4 and 10 years,and in 10 years.Both have negative growth in the future.In the 20-60cm soil layer,the direction of change of the four heavy metals during different planting years is inconsistent,and the rate of change is small,indicating that the heavy metal content of the soil is less affected by planting years.The evaluation results of the pollution load index showed that the overall soil risk of the facilities in the study area was low,and the soil was not contaminated by Cu,Zn,and As.However,the Cd pollution load index was generally higher,and some of the sample sites reached a moderate level of pollution.The Cu,Zn,as pollution load index varies little among different planting years,and Cd fluctuates greatly.In 0-20cm plough layer soil,the pollution load index of open field and 16 years is relatively low,4 years,10 years and 12 years are relatively high.The analysis of spatio-temporal changes in soil nutrients showed that as the soil depth of facilities increased,the contents of organic matter,nitrogen,phosphorus,and potassium had a downward trend.Among them,phosphorus and potassium accumulate in the soil tillage layer,and organic matter and nitrogen have the tendency to migrate to the lower layer of soil.The correlation analysis of heavy metals and soil nutrients showed that there were significant positive correlations between Cu,Zn,and Cd,and there was a significant positive correlation between Cu,Cd,P,and organic matter,and there was a clear correlation between P,K,and organic matter.There was no significant correlation with other heavy metals and soil nutrients.This time Cu,Zn,Cd and soil nutrients were homologous.Cu,Zn,and Cd in the soil of the facility may be affected by fertilization during agricultural planting.Maybe derived from parent material.The results of health risk assessment showed that the carcinogenic risk and non-carcinogenic risk of heavy metals in soil were within reasonable limits,indicating that the heavy metals in the study facilities had a low risk of carcinogenic and non-carcinogenic risks and were less harmful to the human body.The level of carcinogenic risk and non-carcinogenic risk are much higher than those of the latter.The health risks of plant soils with planting years of 4 years,10 years,and 12 years were higher than those of other years.The carcinogenic and non-carcinogenic risks of planting soils for 16 years were significantly reduced.Through comparison,it was found that the pollution of the soil by the heavy metals in the facility is greater than the damage to the human body.For the non-carcinogenic risk,the former is 300-400 times that of the latter;for the carcinogenic risk,the former is the latter 30-40 times.The analysis of heavy metal content in vegetables in facilities showed that the content of heavy metals in vegetables decreased in order of Zn>Cu>Cd>As.The average concentration of Cd was higher than that of Chinese food standard.55.6%of the samples exceeded the permitted limit.The average concentration of As in vegetables was significantly lower than the tolerance limit.The change trend of heavy metals in vegetables is similar to that of the above soil,indicating that heavy metals in soil affect the heavy metals in vegetables.The results of vegetable health risk assessment showed that the intake of heavy metals was Zn>Cu>Cd>As.EDI in adults is higher than that in children.Heavy metals do not produce significant harmful risk in adults and children.