Changes in the microbial activity and thermal properties of soil treated with sodium fluoride

• Impact of NaF in six doses (1105–11051 mg kg−1 DM) on soil properties was studied.
• Successive NaF doses increased pH and electrolytic conductivity of soil.
• Fluoride doses up to 6631 mg kg−1 DM soil increased the content of microbial biomass.
• Doses above 6631 mg kg−1 DM soil inhibited microbial growth and glucose degradation.

The presence of sodium fluoride in soil can determine its physicochemical and thermal properties as well as microbial activity. In this study, sodium fluoride was introduced to soil in six doses: 1105, 2210, 4420, 6631, 8841 and 11051 mg kg−1 DM soil. Changes in pH, electrolytic conductivity, soil microbial biomass (SIR-SMB) and glucose biodegradation parameters were determined in soil samples containing different doses of sodium fluoride. Soil microbial activity was investigated by the modified SIR3 (AA) method and isothermal microcalorimetry. Soil samples containing higher doses of sodium fluoride were characterized by elevated pH and increased electrolytic conductivity. Our results revealed that soil microbial activity and the kinetics of glucose decomposition were determined by sodium fluoride concentrations in soil. Sodium fluoride doses of 1105–6631 mg kg−1 DM soil increased the content of microbial biomass and stimulated glucose degradation in soil samples relative to the control (without sodium fluoride). The two highest doses of sodium fluoride (8841 and 11051 mg kg−1 DM soil) reduced SIR-SMB and inhibited degradation of organic matter.