Contamination characteristics and health risk assessment of heavy metals in soil and tea in the Jiaodong main tea producing area

ObjectiveThis study aimed to analyze the contamination characteristics of heavy metals in soil and tea leaves in the Jiaodong hilly tea-producing areas.MethodsA total of 340 soil samples and 173 tea samples from 2015 to 2021 were collected from Haiyang， Shandong Province. The contents of Pb， Cd， total Hg， and total As were detected. The single-factor contamination index method， the Nemerow comprehensive contamination index method， and the Target Hazard Quotient were used to evaluate the contamination level according to the grading standard of agriculture product quality. Pearson correlation analysis and principal component analysis were used to analyze the relationship between heavy metals and their sources in soil and tea.ResultsThe average contents of Pb， Cd， As， and Hg were 29.00， 0.107， 8.852， and 0.023 mg/kg， respectively， and Pb content was the highest in the study area soil. The average value of all heavy metal elements did not exceed the limit value in GB 15618—2018 ［the standard for the control of soil pollution risk of agricultural land （Trial）］， while the maximum values of Pb and Cd exceeded the national standard. The average values of As and Pb exceeded or reached the background values for soil in the eastern Shandong Province. The average and maximum values of heavy metal elements in tea did not exceed GB 2762—2017 （National standard for food safety-limit of pollutants in food and limit of Cr， Cd， Hg， As， and fluoride in tea）. The average contents of Pb， Cd， Hg， and As in tea were 0.286， 0.041， 0.001， and 0.037 mg/kg， respectively. The detection rates of Pb， Cd， Hg， and As were 95.95%， 96.53%， 13.87%， and 30.64% in tea， respectively. The mean value of heavy metals in tea decreased in the order of Pb > Cd > As > Hg. The single factor pollution index of the four elements was less than 0.6， PPb （0.057 2） > PCd （0.041 7） > PAs （0.018 7） > PHg （0.005 3）， and all values were at the safe level. The comprehensive pollution index of tea was 0.045 9， and the pollution level was classified as safe. Black tea had higher pollution levels than green tea. Pb and Cd had higher pollutant sharing rates.ConclusionThe sources of Cd， Pb， Hg， and As in the soil may have a common origin. As and Pb in soil exhibited mixed sources， while Cd and Hg originate from industrial “three wastes” and agricultural production. The sources of Pb， Cd， Hg， and As in tea have little correlation with heavy metals in the soil. Dietary exposure to heavy metals in tea leaves in the Jiaodong hilly tea-producing areas is at a safe level.