An optimised extraction and cleanup method for the analysis of pesticide in natural water samples is presented. Sixteen pesticides of different polarity and from the different chemical classes (organophosphates, triazines, benzimidazoles, carbamates, carbamides, neonicotinoides, methylureas, phenylureas and benzohydrazides), most frequently used in Serbia, were selected for the analysis. Liquid-phase microextraction in a single hollow fibre (HF-LPME) has been applied for sample preparation. The concentrations of pesticides were determined using HPLC-MS/MS method with electrospray ionisation. The extraction behaviour and selection of the experimental conditions was predicted based on log D and pK(a) values of targeted pesticides, which were calculated applying the computer software ACD/Labs PhysChem Suite v12. The influence of the donor pH and concentration of pesticides, organic phase composition as well as the extraction time on the extraction efficiency was investigated. Optimum extraction conditions were evaluated with respect to the investigated parameters of the extraction. The extraction method was validated for 10 out of 16 studied pesticides. Linear range of the pesticides was 0.1-5 microg L(-1) with the correlation coefficient from 0.991 to 0.9998, and the relative standard deviation for three standard measurements was between 0.2 and 11.8%. The limits of detections ranged from 0.026 to 0.237 microg L(-1) and the limits of quantifications from 0.094 to 0.793 microg L(-1). The optimised two-phase HF-LPME method was successfully applied for determination of moderately polar as well low-polar pesticides in the environmental water samples.
The removal of Pb(II),
Cd(II), Cu(II), and Zn(II) from aqueous
solutions using (un)modified Serbian interstratified montmorillonite/kaolinite
clay as an adsorbent was investigated. The clay was modified by mechanochemical
activation for different time periods. X-ray diffraction patterns
and particle size distributions were used to characterize the samples.
Batch adsorption studies were conducted to optimize various conditions.
The adsorption equilibrium was established within 60 min, and the
maximum adsorption occurred in the pH range of 4.5–6.5. The
milled clays exhibited greater equilibrium adsorption capacities (q
e) for all of the metals than the raw clay.
A difference in q
e values for clays milled
for 2 and 19 h could be observed only for initial concentrations (C
i) of ≥100 mg dm–3.
This was related to the amorphization (i.e., exfoliation) of 19-h-milled
clay particles. The adsorption equilibrium data of heavy metals on
both raw and modified clays fit the Langmuir equation, although there
were changes in the microstructure of the clay. The mechanochemical
treatment of the clay reduced the amount of adsorbent necessary to
achieve a highly efficient removal of heavy metals by a factor of
5. Thus, the mechanochemically treated interstratified clay can be
considered as an efficient adsorbent for the simultaneous removal
of divalent heavy metals.
Commercially available pesticides were examined as Mus musculus and Homo sapiens acetylcholinesterase (mAChE and hAChE) inhibitors by means of ligand-based (LB) and structure-based (SB) in silico approaches. Initially, the crystal structures of simazine, monocrotophos, dimethoate, and acetamiprid were reproduced using various force fields. Subsequently, LB alignment rules were assessed and applied to determine the inter synaptic conformations of atrazine, propazine, carbofuran, carbaryl, tebufenozide, imidacloprid, diuron, monuron, and linuron. Afterwards, molecular docking and dynamics SB studies were performed on either mAChE or hAChE, to predict the listed pesticides’ binding modes. Calculated energies of global minima (Eglob_min) and free energies of binding (∆Gbinding) were correlated with the pesticides’ acute toxicities (i.e., the LD50 values) against mice, as well to generate the model that could predict the LD50s against humans. Although for most of the pesticides the low Eglob_min correlates with the high acute toxicity, it is the ∆Gbinding that conditions the LD50 values for all the evaluated pesticides. Derived pLD50 = f(∆Gbinding) mAChE model may predict the pLD50 against hAChE, too. The hAChE inhibition by atrazine, propazine, and simazine (the most toxic pesticides) was elucidated by SB quantum mechanics (QM) DFT mechanistic and concentration-dependent kinetic studies, enriching the knowledge for design of less toxic pesticides.
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