Synchronization of the astronomical time scales in the Early Toarcian: a link between anoxia, carbon-cycle perturbation, mass extinction and volcanism

International audienceThe Late Pliensbachian–Early Toarcian is a pivotal time in the Mesozoic era, marked by pronounced carbon-isotope excursions, biotic crises and major climatic and oceanographic changes. Here we present new high-resolution carbon-isotope and magnetic-susceptibility measurements from an expanded hemipelagic Late Pliensbachian–Early Toarcian section from the Middle Atlas Basin (Morocco). Our new astronomical calibration allows the construction of an orbital time scale based on the 100-kyr eccentricity cycle. The Early Toarcian Polymorphum Zone contains 10 to 10.5 repetitions of the 100-kyr eccentricity both in the carbon-isotope and the magnetic-susceptibility data, leading to an average duration of 1.00±0.081.00±0.08 myr. We also show that the Late Pliensbachian–Early Toarcian global carbon-cycle perturbation has an average duration of 0.24±0.020.24±0.02 myr. These durations are comparable to previous astrochronological time scales provided for this time interval in the most complete sections of the Tethyan area, and longer than what has been provided in condensed sections. Anchoring this framework on published radiometric ages and astrochronological time scales, we estimate that the carbon-cycle perturbation of the Late Pliensbachian–Early Toarcian corresponds with the early phase of the Karoo and Chonke Aike large igneous provinces. Likewise, our new age constraints confirm that the Toarcian oceanic anoxic event is synchronous to the main phase of the Ferrar volcanic activity. Thus, these successive and short phases of the volcanic activity may have been at the origin of the successive phases of the mass extinctions observed in marine biotas in the Pliensbachian and Toarcian times

An easy-to-use colorimetric enzymatic test-system for organophosphorus insecticides detection in olive oil

International audienceImmobilization of a low amount of electric eel acetylcholinesterase on microtiter plates by bioencapsulation in a sol-gel composite led to the preparation of a simple colorimetric enzymatic-assay for pesticides detection in olive oil. This bioassay has been used to carry out inhibition studies with three pesticides mainly used in the treatment of olive trees: Malaoxon, Methidathion-oxon and Omethoate, and tested using standard solutions and real samples of olive oil. The developed bio-tools showed a good reproducibility and stability as well as good analytical performances with limits of detection at least 10 times less than the maximum residue limit tolerated by international regulations. The obtained LODs were as low as 10-9 M for the widely used pesticide Malaoxon, 10-8 M for Methidathion oxon and 10-7 M for Omethoate. The developed test was designed for fast detection of the three target insecticides in such a complex matrix as olive oil without a laborious pre-treatment and after a simple liquid-liquid extraction, which demonstrate the potentiality of this technique to be used for commercial purpose

Enzymatic biosensor associated with Molecularly Imprinted Polymers for sensitive and selective detection of organophosphorus insecticides in olive oil

International audience5 different bio-tools have been developed for sensitive detection of three organophosphorus insecticides mainly used for the treatment of olive trees: Malaoxon, Omethoate and Methidathion-oxon. The systems are based on the immobilization of electric eel acetylcholinesterase on screen-printed electrode (SPE) and microtiter plates by 3 different methods of immobilization. These developed systems were optimized with laboratory samples and then tested on natural samples of olive oil after a simple liquid-liquid extraction. Among these five systems designed, the amperometric biosensor based on acetylcholinesterase immobilized by bioencapsulation in a sol-gel matrix presented the best performance in terms of operational stability, storage stability, reproducibility, and it proved to be best suited for the determination of insecticides in real samples of olive oil. This biosensor has been associated with a highly selective extraction method based on the use of Molecularly Imprinted Polymers (MIPs) to improve selectivity. The results showed that the association MIPs-biosensor can selectively detect and quantify the three organophosphorus insecticides in such a complex matrix as olive oil, with limits of detection much lower than the maximum residue limit tolerated by international regulations

Studies on the adsorption of heptamolybdate ions on AISI 304 stainless steel from acidic HCl solution for corrosion inhibition

Surface interaction of heptamolybdate ions Mo7O24 6- on ASI 304 stainless steel (SS) greatly reduces the corrosion rate of the material in acid environments, providing an environmentally-friendly inhibitor system. Corrosion inhibition properties have been studied in naturally aerated 0.5 M HCl solution from weight loss measurements. The influences of inhibitor concentration and solution temperature were investigated. The percentage inhibition efficiency, SW(%), increased for increasing concentrations of the ionic inhibitor species. Conversely, the increase of temperature decreased the inhibition efficiency. That is, the corrosion rate, vcor, was faster at higher temperature whereas it was slower for increasing inhibitor concentrations. The adsorption of the inhibitor ions onto the SS surface was found to follow the Langmuir adsorption isotherm. The values of the standard adsorption free energy, 0 ads G , are consistent with a spontaneous physisorption mechanism of the inhibitor ions on the surface of the steel

Inhibition of the pitting corrosion of 304 stainless steel in 0.5 M hydrochloric acid solution by heptamolybdate ions

The corrosion inhibition effect of heptamolybdate ions on 304 stainless steel in 0.5 M hydrochloric acid solution at 298 K was investigated using gravimetric, electrochemical and optical microscopy methods. Increasing inhibitor concentration led to significant reduction in the corrosion rate of stainless steel, withinhibitor efficiency values above 90%. The adsorption of the inhibitor onto the steel surface is described using the Langmuir adsorption isotherm. The value of the free energy of adsorption determined at 298 K (ΔG° = -31.1 kJ mol-1) characterizes the adsorption process of heptamolybdate ions on the surface of the metal