The Effect of Titanium Dioxide Nanoparticles on Carbon Dynamics in Antimony-Contaminated Soil

Heavy metals affect the dynamics of organic carbon by contaminating soil and altering its chemical and biological properties. For this purpose, a split factorial experiment was conducted with three replications. Experimental factors included Antimony at four levels (0, 25, 50, and 100 mg/kg), TiO2 nanoparticles as an adsorbent at three levels (0, 0.25, and 0.5 % by weight), and time at eight levels (the first month to the eighth month). Results showed that the basal respiration decreased from the first month to the eighth month of incubation and the highest basal respiratory rate was obtained from the first month of incubation and the lowest one was belong to the eighth month of incubation with a significant difference of 27.81%. The highest and the lowest organic matter degradation rates were obtained in control and 50 mg/kg antimony without nanoparticle application with 16.57% difference. By increasing antimony levels, the rate of degradation of organic matter decreased sharply, but by increasing the levels of contaminant, the application of 0.5 % (w/w) nanoparticles caused to increase the rate of organic matter decomposition. The highest value of half-life and mean residence time of carbon in the soil were obtained from 50 mg/kg without adsorbent treatment and the lowest value was obtained from 25 mg/kg with 0.5% (w/w). According to the results of this study it can be stated that the application of 0.5 % (w/w) TiO2 adsorbent increased the rate of decomposition of organic matter but decreased the half-life and mean residence time of carbon in the soil. At the higher contaminant levels (100 mg/kg of antimony), compared to the lower levels (50 and 25 mg/kg), the adsorbent surface lost its efficiency because of saturation with the contaminant, therefore for higher level of contaminant application, higher level of adsorbent (more than the 0.5% (w/w) TiO2) should be used.