BACKGROUND The Luanchuan Mo-Pb-Zn polymetallic ore concentration area, located in Henan Province, China, has a long-term history of mining activities. Heavy metals have been liberated during mining, which induces heavy metal pollution of water and soil near the mines. There have been many studies about the pollution of heavy metals by mining activities, but it is still unclear as to the impact of various mine types in a polymetallic ore concentration area on accumulation of heavy metals in soil.

OBJECTIVES To study the impact of various mine types on accumulation of soil heavy metals, pollution level and ecological risk, and to identify the sources of soil heavy metals.

METHODS A total of 95 surface soil samples were collected from 29 soil profiles along the rivers in five typical basins in the Luanchuan Mo-Pb-Zn polymetallic ore concentration area, Henan Province, China. Mo, Hg, As, Cd, Cr, Cu, Pb and Zn in soil were measured by polarography, atomic fluorescence spectrophotometry (AFS) and inductively coupled plasma-mass spectrometry (ICP-MS). The I_geo, Nemerow index and potential ecological risk index were used to study the accumulation, pollution level and source apportionment of heavy metals.

RESULTS The results showed that Mo was the main pollutant, and part of the soil was obviously polluted by Hg. Cd, Pb, Zn, Cu and As in soil were also affected by the mining activities in the study area to some extent. Accumulation extent of heavy metals in soil from various river basins followed Beigou River > Yu River > Shibao River > Taowanbei River > Yi River. Soil samples from the Beigouhe River Basin were heavily polluted and posed a moderate risk level. In addition, soil samples from other river basins contained a low level of pollution and ecological risk. However, some sites which possessed a higher pollution level and ecological risk were found in all of the river basins. It was worth noting that soil samples near a river in a soil profile can accumulate more heavy metals than other soil samples, indicating that accumulation of heavy metals in the soil is affected by the river. The main sources of heavy metals in the surface soil were parent rock weathering (32.9%), lead zinc mining activities of Pb/Zn mines (30.6%), mining activities of Mo mines (26.8%), and mining activities of Au (9.7%), respectively.

CONCLUSIONS Mining activities cause heavy metal accumulation in the soil to some extent, and Mo and Hg pollution more heavily. Pb/Zn mines account for 30.59% of the source of soil heavy metals, which are higher than Mo mines and Au mines, indicating mining activities of Pb/Zn should be paid more attention. More heavy metals from parent rock (32.9%) indicate that it is necessary to measure the speciation of soil heavy metals and concentrations of heavy metals in crops.