Objective  In order to provide the scientific guidance for risk assessment and safety utilization of polluted field in irrigation areas, the distribution of heavy metals in soil aggregates of the sewage irrigation area was studied.

  Method  Winter wheat planting farmland in Xinxiang County, Henan Province, was taken as the research object. Dry screening method was used to obtain different sizes of soil aggregates, and the distribution characteristics of total and available contents of heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) in soil aggregates were analyzed using mass loading factor and distribution factor.

  Result  The results showed that pH, organic matter, cation exchange capacity, and conductivity ranged from 7.38 to 9.07, 11.04 to 42.99 g kg⁻¹, 5.80 to 14.81 cmol kg⁻¹, 124.77 to 394.70 μS cm⁻¹, respectively. The variation coefficient of pH was 3%, belonging to weak variation. And the variation coefficients of soil organic matter, cation exchange capacity and electrical conductivity were 17%, 15% and 24%, respectively, being low variation. The content of Cr in 1-0.5 mm aggregate was the highest, which was 253.98 mg kg⁻¹. The contents of Ni, Cu, Zn, Cd and Pb in 0.5-0.25 mm aggregate were higher, with 22.49 mg kg⁻¹, 6.59 mg kg⁻¹, 18.99 mg kg⁻¹, 1.12 mg kg⁻¹ and 22.88 mg kg⁻¹, respectively. The distribution factors of Cr, Ni, Zn and Pb in all aggregates were less than 1, the distribution factor of Cu in 0.5-0.25 mm aggregates was greater than 1, and while the distribution factor of Cd in 8-5 mm, 5-2 mm, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm and ( < 0.25 mm) aggregates was greater than 1. The mass loading factors of heavy metals in different particle sizes were 5-2 mm > 8-5 mm > 2-1 mm > ( < 0.25 mm) > 1-0.5 mm > 0.5-0.25 mm. The contents of Cr and Zn were the highest in the aggregates with particle size < 0.25 mm, and while Ni, Cu, Cd and Pb was the highest in 0.5-0.25 mm aggregates. The total contents of heavy metals in each particle size was significantly positively correlated with its available content (P < 0.05).

  Conclusion  Total and available contents of heavy metals were more distributed in small size of soil aggregates, and they exhibited significantly correlation with each other, while the values mass loading factor were higher in larger size of soil aggregates. The number of distribution factor of Cd was the highest than other heavy metals.