Quantitative understanding the kinetics of toxic ion reactions with various heterogeneous ferrihydrite binding sites is crucial for accurately predicting the dynamic behavior of contaminants in environment. In this study, kinetics of As(V), Cr(VI), Cu(II), and Pb(II) adsorption and desorption on ferrihydrite was studied using a stirred-flow method, which showed that metal adsorption/desorption kinetics was highly dependent on the reaction conditions and varied significantly among four metals. High resolution scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that all four metals were distributed within the ferrihydrite aggregates homogeneously after adsorption reactions. Based on the equilibrium model CD-MUSIC, we developed a novel unified kinetics model applicable for both cation and oxyanion adsorption and desorption on ferrihydrite, which is able to account for the heterogeneity of ferrihydrite binding sites, different binding properties of cations and oxyanions, and variations of solution chemistry. The model described the kinetic results well. We quantitatively elucidated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites and the formation of various surface complexes controlled the adsorption and desorption kinetics at different reaction conditions and time scales. Our study provided a unified modeling method for the kinetics of ion adsorption/desorption on ferrihydrite.

The thermal stability of antibiotics commonly detected in food is reviewed. To quantify degradation, 2 major techniques have been reported: liquid chromatography-based methods and microbiological tests. As the degradation products may also display some antimicrobial activity, microbiological tests may not be considered accurate analytical methods for quantifying antibiotic residues' degradation. Degradation percentages are summarized for different antibiotics and for various media (water, oil, milk, and animal tissues). Studies presented in the literature confirm that the thermal degradation of β-lactams, quinolones, sulfonamides, and tetracyclines can be described using a first-order kinetic model. Degradation rates, k, derived for this model for liquid matrix (water) at 100 °C, followed the general trend amongst antibiotic classes: β-lactams = tetracyclines (most heat-labile) > lincomycin > amphenicols > sulfonamides > oxfendazole > levamisole (most heat-stable). Although thermal processing results in a decrease in the concentration of parent antibiotic residues, degradation by-products have not been properly characterized to date. As some of these products were shown to be hazardous, further investigation is needed to determine their impact on food safety and human health. It is therefore currently difficult to definitively conclude whether or not antibiotic degradation during food processing is necessarily beneficial in terms of food safety.

Urea complexation (UC) and the molecular distillation (MD) technique were applied jointly to purify eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from sardine oil ethyl esters (SOEE). Response surface methodology (RSM) was used to measure the influences of the variables to the responses and the optimal conditions. Regression analysis and variance analysis of the models demonstrated that each multinomial correctly represented the relationships between the responses and the variables. The urea-to-SOEE ratio was much more significant than crystallization temperature in UC, and the quadratic term of rotation speed of swept-surface scrapers was the most significant variable in MD. Optimal UC conditions were 1.9:1 urea-to-SOEE ratio and -1°C crystallization temperature at which the purity and total recovery of EPA and DHA were 65.6 % and 46.8 %, respectively. The best conditions predicted for MD were 75°C distillation temperature, 54.8°C preheat temperature, 4.5°C condensation temperature, and 307 rpm rotation speed at which the purity of EPA and DHA was 83.5 %. The predicted values were verified to be reasonably close to the experimentally observed values.

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