This paper is the result of environmental geological survey engineering.

Objective Ning'an City, Heilongjiang Province, is one of the 83 key protected counties and cities for black soil nationwide. Investigating and characterizing the distribution characteristics of heavy metal elements in soil and the environmental quality status in Ning'an City hold significant importance for developing the "100-kilometer northeast asian high-end food, agricultural products, and cultural ecological industry corridor".

Methods 70 surface and deep soil samples were collected systematically to determine the contents of eight heavy metals, including Zn, Ni, Cd, Cu, Cr, Pb, As and Hg. Data statistics and geospatial analysis were used to reveal their distribution and enrichment characteristics. Correlation and principal component analysis were used to trace the sources of heavy metals. The cumulative geological index and Nemerow comprehensive index were used to evaluate soil pollution.

Results (1) The coefficient of variation of Hg, Cd, Ni and As heavy metals in Ning'an area was more than 36%, which was greatly affected by human activities. (2) Ni, Cu and Cr are mainly derived from deep parent rock or weathered material; Pb and As are mainly affected by agricultural activities; Zn, Cd and Hg are mainly affected by human activities and geological background. (3) The enrichment degree of different heavy metal elements in deep soil in Ning'an area is quite different, and most of them are non enriched and slightly enriched. (4) The evaluation results of geological cumulative index method showed that except for the slight pollution of Cr, which accounted for 63.77%, the slight pollution of other heavy metals did not exceed 25%. (5) The results of the nemerow comprehensive pollution index method indicate that the ranking of individual pollution indices for heavy metal elements in Ning'an region is Cr > Ni > As > Cd > Cu > Zn > Pb > Hg. Except for Hg (which remains clean) and Cr (which is moderately polluted), the individual pollution indices of heavy metals in the remaining soils are primarily lightly polluted.

Conclusions There is a slight pollution problem of heavy metals in the soil of Ning'an area. It is suggested to strengthen the preventive measures in mining operations, agricultural production and other human activities.