Objective The aims were to clarify the status of heavy metal contamination and the associated ecological and human health risks in farmland soils surrounding mining areas in eastern Inner Mongolia.

Methods Surface soil samples from farmland at a depth of 0 - 20 cm were collected and analyzed. The concentrations and spatial distribution characteristics of five heavy metals (Cr, Cd, As, Pb and Hg) were systematically investigated. The degree of heavy metal pollution, potential ecological risk, and human health risk were comprehensively assessed using the geo-accumulation index, the Nemerow comprehensive pollution index, the potential ecological risk index and a human health risk assessment model.

Results ① The mean concentrations of Cr, Cd, As and Pb in the study area were higher than the soil background values of Inner Mongolia, with overall levels approximately 1.4 times than the background values. ③ The geo-accumulation index assessment indicated that Cd exhibited a certain degree of enrichment in the soils of the study area, with approximately 70% of the sampling sites classified as slightly polluted. In comparison, about 30% of the sampling sites showed slight pollution by Pb, Cr and As. ③ The Nemerow comprehensive pollution index showed that 99% of the soils in this area were classified as unpolluted, indicating that the overall heavy metal contamination level was low and remained within the safe range. ④ The potential ecological risk assessment revealed that the farmland soils generally exhibited a low ecological risk level. However, moderate to considerable ecological risks associated with Cd and Hg were observed at several individual sampling sites. ⑤ The human health risk assessment indicated that the non-carcinogenic risks resulting from all exposure pathways were within acceptable limits, whereas the combined carcinogenic risk posed by multiple heavy metals exceeded the acceptable threshold. Health risks to children were notably higher than those to adults. In addition, the risk contributions of different heavy metals varied across exposure pathways.

Conclusion Overall, the distribution of heavy metals in the farmland soils of the study area was characterized by a generally low level of contamination with localized enrichment at certain sampling sites. The contamination levels varied among different elements, with Cd identified as the principal potential risk factor, while Hg and As also warranted attention at a few individual sites. In general, the study area was dominated by non-polluted, slightly polluted and low ecological risk conditions. However, sites exhibiting relatively high risk should be prioritized in subsequent integrated prevention, control and risk management efforts.