Isothermal Microcalorimetry:A Review of Applications in Soil and Environmental Sciences

Isothermal microcalorimetry provides thermodynamic and kinetic information on various reactions and processes and is thereby a powerful tool to elucidate their mechanisms. Certain improvement in isothermal microcalorimetry with regard to the studies on soil and environmental sciences is briefly described. This review mainly focuses on the use of microcalorimetry in the determination of soil microbial activity, monitoring the toxicity and biodegradation of soil organic pollutants, the risk evaluation of metals and metalloids, the heat effect of ion exchange and adsorption in soil, and environmental researches. Promising prospects for the applications of the technique in the field are also discussed.

Effect of Selected Organic Acids on Cadmium Sorption by Variable- and Permanent-Charge Soils

Batch equilibrium experiments were conducted to investigate cadmium (Cd) sorption by two permanent-charge soils, a yellow-cinnamon soil and a yellow-brown soil, and two variable-charge soils, a red soil and a latosol, with addition of selected organic acids (acetate, tartrate, and citrate). Results showed that with an increase in acetate concentrations from 0 to 3.0 mmol L-1, Cd sorption percentage by the yellow-cinnamon soil, the yellow-brown soil, and the latosol decreased. The sorption percentage of Cd by the yellow-cinnamon soil and generally the yellow-brown soil (permanent-charge soils) decreased with an increase in tartrate concentration, but increased at low tartrate concentrations for the red soil and the latosol. Curves of percentage of Cd sorption for citrate were similar to those for tartrate. For the variable-charge soils with tartrate and citrate, there were obvious peaks in Cd sorption percentage. These peaks, where organic acids had maximum influence, changed with soil type, and were at a higher organic acid concentration for the variable-charge soils than for the permanent charge soils. Addition of cadmium after tartrate adsorption resulted in higher sorption increase for the variable-charge soils than permanent-charge soils. When tartrate and Cd solution were added together, sorption of Cd decreased with tartrate concentration for the yellow-brown soil, but increased at low tartrate concentrations and then decreased with tartrate concentration for the red soil and the latosol.

Effects of Ionic Strength and Sesquioxides on Adsorption of Toxin of Bacillus thuringiensis subsp.kurstaki on Soils

Chemical reactions and fate of the toxins of Bacillus thuringiensis(Bt) in the soil environment are causing increasing concerns due to the large-scale cultivation of transgenic Bt plants.In this study,the effect of ionic strength(0-1 000 mmol kg 1) adjusted by NaCl or CaCl 2 on adsorption of Bt toxin by a lateritic red soil,a paddy soil and these soils after chemical removal of organic-bound or free Fe and Al oxides,as well as by pure minerals(goethite,hematite and gibbsite) which are widespread in these soils,were studied.The results indicated that when the supporting electrolyte was NaCl,the adsorption of Bt toxin by the lateritic red soil and paddy soil increased rapidly until the ionic strength reached 250 mmol kg 1 and then gradually slowed down with the increase of ionic strength;while in case the supporting electrolyte was CaCl 2,the adsorption of Bt toxin enhanced significantly at low ionic strength(< 10 mmol kg 1) and then decreased as the ionic strength increased.The adsorption of Bt toxin by the tested minerals and soils after the removal of organic-bound or free Fe and Al oxides also increased with increasing ionic strength controlled by NaCl.Removing organic-bound Fe and Al oxides obviously increased the adsorption of Bt toxin in the tested soils.Differently,removing free Fe and Al oxides increased the Bt adsorption by the paddy soil,but decreased the adsorption by the lateritic red soil.The study indicated that the varieties of ionic strength and the presence of Fe and Al oxides affected the adsorption of Bt toxin by the soils,which would contribute to the further understanding of the fate of Bt toxin in the soil environment and provide references for the ecological risk assessment of transgenic Bt plants.

Effect of Cobalt-Doped Framework on Formation of Todorokite from Layered Manganese Oxides with Mg^(2+)/Co^(2+) Ions as Template

Cobalt(Co)exists in significant quantities in naturally occurring manganese(Mn)oxides and alters the growth of Mn oxide crystals.Four-layered Mn oxides,Na-buserite(Na-bus)and three Co-doped Na-buserite samples prepared from oxidation of Mn(OH)2 with 5%,10%,and 20% Co/(Mn+Co)molar ratios(5Co-Na-bus,10Co-Na-bus,and 20Co-Na-bus),were used to prepare todorokite,a common Mn oxide on the Earth's surface,using Mg2+/Co2+ ions as a template.The results showed that todorokites could be obtained by reflux treatment of Mg2+-exchanged non-doped Na-buserite and three Co-doped Na-buserites at atmospheric pressure.However,the formation of todorokites was prohibited by reflux treatment of Co2+-exchanged Na-bus,5Co-Na-bus,and 10Co-Na-bus samples.Instead,todorokite was obtained by the reflux treatment of Co2+-exchanged 20Co-Na-bus samples under atmospheric pressure.X-ray photoelectron spectroscopy analysis showed that doped Co existed as Co3+in the MnO6 layers of doped Na-buserites.The amount of substituted Co3+ in the MnO6 layers may play a key role in the conversion of buserite to todorokite using Co2+ ions as a template.