This paper is the result of agricultural geological survey engineering.

Objective Cadmium is a common harmful metal contaminant in soil environment, and it is a non-essential element of plants. Researching on the cadmium content and potential ecological risk in topsoil of cultivated land can provide environmental geological basic data for green agricultural development and ecological environment management in Tongzi County.

Methods This paper is based on the data of cadmium content in topsoil samples obtained from the quality geochemical survey of cultivated land in Tongzi County. Single factor pollution index method and potential ecological hazard index method were used to evaluate the ecological risk of topsoil cadmium. The risk degree of cadmium in topsoil was classified according to Soil Environmental Quality-Risk Control Standards for Agricultural Land Soil Pollution (Trial). The factors affecting topsoil cadmium and its biological availability were systematically discussed in this paper.

Results The average cadmium content in the topsoil of cultivated land in the study area was 0.51 mg/kg. The background value of cadmium content in the topsoil of cultivated land in the study area was 0.35 mg/kg, which was 2.33 times that of the national soil. The potential ecological risk of topsoil cadmium is basically in a safe state, mainly pollution-free and risk-free. The topsoil cadmium high value area is mainly distributed in the parent rock area of the Permian Qixia, Maokou and Longtan Formations. Cadmium content is high in the soil formed by limestone weathering. The biological enrichment capacity of cadmium in rice was relatively high. The order of bioenrichment ability was rice > pear > square bamboo shoots.

Conclusions The study area belongs to the background area of high cadmium in soil. The distribution and content of cadmium in soil are controlled by strata and parent rock. The area of high cadmium value in topsoil is closely related to the exposure of Permian limestone parent rock area. The content of cadmium in weak acid-alkaline soil is higher than that in acidic soil. Rice is relatively easy to accumulate cadmium.