Magnetic susceptibility as a proxy for detection of total petroleum hydrocarbons in contaminated wetlands.

Soil petroleum hydrocarbon contamination in the wetlands could cause ecological risk, especially through leakage into water reservoirs. So, the detection of the spatial variability of total petroleum hydrocarbons (TPH) in these soils is very crucial. The variability of TPH and its associations with magnetic susceptibility (χlf) in contaminated soils around the Shadegan pond in southern Iran was investigated. TPH varied from 2.1 to 18.1% (w/w), by the variation of χlf from 14.08 to 713.93 × 10-8 m3 kg-1. The highest variability (coefficient of variation, CV = 107.12%) was obtained for χlf indicating significant impacts of magnetic minerals induced by crude oil contamination. High positive correlations were detected among TPH, χlf, and different forms of iron (Fed: extracted by CBD, Feo: extracted by oxalate, and Fet: total iron). The results of mineralogy by powdery XRD and scanning electron microscopy (SEM), also revealed the formation of ferrimagnetic minerals (magnetite, maghemite) during the biodegradation of petroleum hydrocarbons. The stepwise multiple regression analysis showed that χlf and Fed made a great contribution and could explain about 74% of TPH variability in the studied sites. For the extension of this cost-effective and rapid technique, further work is needed to assay saturation isothermal remnant magnetization and isothermal remanet magnetization in contaminated sites.

Heavy metals content and distribution in basil (Ocimum basilicum L.) as influenced by cadmium and different potassium sources.

Despite the fact that cadmium (Cd) is a non-essential element for plants, it can influence nutrients and affect human health. Potassium (K) can influence the transportation of heavy metals (HMs) in soil-plant systems. Here, a greenhouse experiment was conducted to evaluate the effect of Cd and K fertilizers on the different partitioning forms of HMs, their concentrations, uptake in the shoots and roots of Ocimum basilicum. Treatments comprised 2 levels of Cd (0 and 40 mg kg-1) and three levels of K (0, 100, and 200 mg kg-1) from three sources, i.e. KCl, K2SO4, and K-nano-chelate. 40 mg Cd kg-1 increased the shoot (above ground parts) Cd concentration. Addition of K as KCl, K2SO4, and K-nano-chelate increased the presence of Cd in shoots by 86, 82 and 76%, respectively, compared to the control. Using the nano-chelate of K can increase the accumulation of Cd in plants grown on contaminated soils to lesser content than that of the other forms of K. Application of 40 mg Cd kg-1 reduced the concentration of Zn, Cu, and Mn in the shoot, but increased shoot Fe concentration. Transfer factor (TF), which is the ratio of metal concentration in shoot to its concentration in root, of the studied HMs, was significantly affected by Cd and K treatments. Therefore, the proper form and dose of chemical fertilizers should be applied in Cd-contaminated soils.

Reversible surface two-electron transfer reactions in square wave voltcoulommetry: application to the study of the reduction of polyoxometalate [PMo12O40]3- immobilized at a boron doped diamond electrode.

Reversible surface two-electrons transfer reactions (stepwise processes) are analyzed using square wave voltcoulommetry (SWVC), which is a variety of square wave techniques based on the measurement of the transferred charge. Such reversible surface redox processes are exhibited by many two-redox center and multicenter biomolecules (proteins, enzymes, ...) and inorganic molecules like polyoxometalates (POMs), which have very interesting applications, mainly as electrocatalysts. Because of the stationary character of the response obtained, the key parameters that govern the cooperativity degree of the two reversible electron transfers (ETs) are the difference between their formal potentials, ΔE(0), and the square wave amplitude, |E(SW)|, whose combined effect sets the two peaks → one peak transition in the response. Working curves based on the variation of the peak parameters (peak potentials, half-peak widths, and peak heights) with ΔE(0) and |E(SW)| are given, from which the formal potentials and the total surface excess can be accurately determined. SWVC has been applied to the study of the reduction of polyoxometalate [PMo12O40](3-) adsorbed at a boron doped diamond electrode (BDD), for which three stable and well-defined reversible charge peaks, corresponding to three cooperative EE processes, are obtained in the interval (0.6, -0.2) V by using low square wave frequencies. From the analysis of these peaks, the values of the total surface excess and the formal potentials of the six ETs have been obtained in aqueous media for two electrolytes: HClO4 and LiClO4.