Characteristics of heavy metals in the soil-wheat system of sewage irrigation area and its health risk assessment

Taking wheat farmland in a waster irrigation area of Henan Province as the research object, soil and wheat grain point-to-point samples were collected to determine the characteristics of heavy metal contents in soil and wheat grain, and then we explored the key factors of soil physio- chemical characteristics that affect uptake of heavy metals in wheat grain. Single target hazard quotient (THQ) and comprehensive target hazard quotient (TTHQ) were used to evaluate the health risk of heavy metals in wheat grains to human health in the study area. The contents of Cu, Zn, Cd, Pb, Cr and Ni in the study area were 6.40, 35.52, 0.95, 24.35, 319.60, and 21.71 mg.kg(-1), Cd, Pb and Cr content exceeded the background value of heavy metal content in Henan Province, and Cr and Cd content exceed the screening value of soil pollution risk control standard of Soil Environmental Quality Control Standards for Soil Pollution Risk on Agricultural Land (GB 15618-2018). The concentrations of Cu, Zn, Cd, Pb, Cr and Ni in wheat grains were 4.14, 28.07, 0.09, 0.45, 0.54, and 0.42 mg.kg(-1), and there were 54, 18, 59 and 5 wheat grain samples of Cd, Pb, Cr and Ni, respectively, exceeded the food safety standard (GB 2762-2017). Nonlinear results showed higher correlation between heavy metals in wheat grains and soil physical and chemical properties. Health risk evaluation showed that THQ of Cu, Zn was 0.50-1.62 and 0.49-1.47, respectively, and the samples of THQ>1 was 29.32% and 17.28% respectively. Cr, Cd, and Pb in some of wheat grain samples exhibited health risks to both adults and children. The mean values of TTHQ for adults and children were 3.30 and 5.58, ranging from 1.38 to 18.15 and 2.30 to 30.66, respectively. The samples of TTHQ > 1 was 100%. THQ and TTHQ risk values showed children > adults.