Interactive effect of radioactive and heavy-metal contamination on soil enzyme activity in a former uranium mine

Radioactivity and heavy metal toxicity of multi-metal deposits coexisting with the element uranium (U) could have long-term adverse impacts on soil biological processes and the health of soil ecosystems. Soil enzyme activities are considered bioindicators for assessing soil health. An experiment was designed to investigate invertase and ß-glucosidase activity in multi-metal deposits. Radioactivity and heavy metals were also investigated during this study. Our results showed that the invertase and ß-glucosidase activities were significantly lower in the core mining area than the control area (p<0.05). Activities of the two enzymes decreased with increasing metal concentrations and radioactivity. Cu and Zn showed significant negative effects on ß-glucosidase and invertase activities in a multi-metal deposit at the study site. A significant nonlinear relationship was recorded between soil enzyme activities, radiation dose (R² = 0.71, 0.63; p<0.05), Zn (R² = 0.34, 0.41; p<0.05) and Cu concentrations (R² = 0.46, 0.45; p<0.05). There were turning points at 1 μGy h⁻¹, 250 μg g⁻¹, and 30 μg g⁻¹ for radiation dose, Zn and Cu contents, respectively. The findings could provide more information regarding the toxic effects of radiation and heavy metals on the soil health of multi-metal deposits, which can more precisely guide environmental protection.