Objective The aims were to investigate the heavy metal pollution and health risk in farmland soil around the southern mining area of Daxing'an Mountains in Inner Mongolia.

Method The topsoil samples (1120) were obtained from the farmland around the mining area in five towns of a certain county. The contents of chromium (Cr), cadmium (Cd), arsenic (As), lead (Pb) and mercury (Hg) were determined in the soils of five towns, and the potential ecological risks of heavy metals in soil were evaluated by potential ecological hazard index. A probability risk assessment model based on Monte-Carlo was introduced to evaluate the health risk of five towns.

Result The results showed that the contents of Cr and Hg of every town was lower than the screening value from soil environment quality risk control standard for soil contamination of agriculture land (GB15618-2018) . The over standard rates of Cd and As were 1.67% and 19.86% in town A, and were 22.22% and 9.88% in town B. The over standard rates of Pb and Cd in town C were 6.06% and 24.24%. There was no over standard of heavy metals in town D, and only 3.03% in town E. Town B and C were at medium ecological risk, while other towns were at low ecological risk. The probability of non-carcinogenic risks to children in towns of A, B, C, D and E were 0.75%, 1.67%, 1.00%, 0.66% and 0.78%, respectively. And that of carcinogenic risks to adults were 3.11%, 7.81%, 24.57%, 0.89% and 2.56%, respectively. The average value of cumulative probability of non-carcinogenic risk in children was higher than that in adults, and that of carcinogenic risk in adults was higher than that in children. Assessment based on deterministic risk would underestimate carcinogenic risk. The main contributing factors to the health risk sensitivity of crowd were oral exposure and body weight. Body weight had negative on children's health, followed by oral exposure. The concentration of Cd and As also had a certain impact on human health risk sensitivity. Oral exposure was the priority control way, and Cd and As were the priority control pollutants.

Conclusion The Cd pollution in the farmland soil of the county was relatively heavy, and the pollution of central town was higher than that of the south and north, showing a moderate ecological risk. The probability of adult cancer risk in the soil was relatively high, presenting a pattern of central>northern>southern. The emission of Cd and As should be controlled at the source of the mining area.