Adsorptive features of acid-treated olive stones for drin pesticides: equilibrium, kinetic and thermodynamic modeling studies.

The adsorption behavior of drin pesticides from aqueous solution onto acid treated olive stones (ATOS) was investigated using stir bar sorptive extraction and gas chromatography coupled with mass spectroscopy. The effects of sorbent particle size, adsorbent dose, contact time, concentration of pesticide solution and temperature on the adsorption processes were systematically studied in batch shaking sorption experiments. Maximum removal efficiency (94.8%) was reached for aldrin (0.5 mg L(-1)) using the fraction 63-100 microm of ATOS (solid/liquid ratio: 1 g L(-1)). Experimental data were modeled by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich isotherm model (R(2)=0.98-0.99) fitted the equilibrium data better than the Langmuir and D-R isotherm models, with low sum of error values (SE=1.4-9.2%). The mean adsorption free energy derived from the D-R isotherm model (R(2)=0.95-0.99) showed that the adsorption of drin pesticides was taken place by weak physical forces, such as van der Waals forces and hydrogen bonding. The calculated thermodynamic parameters, DeltaH, DeltaS and DeltaG prove that drin pesticides adsorption on ATOS was feasible, spontaneous and exothermic under examined conditions. The pseudo first order, pseudo second order kinetic and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated.

Endosulfan sulfate sorption on natural organic substances.

This work proposes a viable remediation method based on the use of natural organic substances (NOSs) that characterize the Mediterranean region to improve the ecological system. A series of experiments, including variable conditions, such as temperature, pH, contact time, and pesticide concentration, were performed to demonstrate the efficiency of endosulfan sulfate removal from water by NOSs. Experimental results showed that the pH and temperature of pesticide solutions negatively affect the adsorption process. The maximum adsorption capacity for a specific initial concentration of endosulfan sulfate (0.5 microg/L) was achieved with Origanum compactum (75%), followed by Cistus ladaniferus and Raphanus raphanistrum (72 and 68%, respectively). The adsorption tests gave very satisfying results and point to the possible application of these supports as a remediation technique to prevent pesticide contamination of aquatic ecosystems.

Endosulfan sulfate mobility in soil columns and pesticide pollution of groundwater in Northwest Morocco.

Groundwater pollution from agricultural practices is a serious environmental and health problem. In this work, stir bar sorptive extraction (SBSE) and gas chromatography (GC) with mass spectrometry (MS) detection were used to determine phytosanitary products in groundwater samples from the Loukkos perimeter in Northwest Morocco. Some pesticides--in particular, endosulfan and its metabolites--were found in water destined for human consumption. Analyses of soil samples were also carried out, and the results showed endosulfan sulfate and endosulfan ether in abundance. Endosulfan sulfate leaching was also performed in undisturbed soil columns to obtain more information on the vertical migration of pesticides used in the perimeter. The kinetic study showed a high recovery rate (73%) after 10 days of experimental work.

Electrochemical analysis of endosulfan using a C18-modified carbon-paste electrode.

Successful applications of different analytical procedures to determine quantitatively endosulfan and its metabolites in aqueous media can be found in recent literature. Fundamentally, they have made use of solid-phase extraction (SPE) and gas (GC) or liquid chromatography (LC), sometimes coupled to mass spectrometry (MS). In this paper, a new and alternative methodology to determine quantitatively endosulfan in aqueous media is reported. A C18-modified carbon-paste electrode has been used to determine voltammetrically endosulfan, despite its unfavourable electrochemical properties and behaviour. The methodology proposed is based on the decrease experienced by the peak intensity corresponding to voltammetric signals of Cu(II) when successive and constant additions of endosulfan are carried out. This decrease is directly proportional to the concentration of endosulfan what allows to perform an indirect quantification of the pesticide. The detection limit obtained is 40 ng l(-1), this value being under the limits specified by European norms and EPA reports.