Lidia Soldà

Assessment of the environmental exposure of honeybees to particulate matter containing neonicotinoid insecticides coming from corn coated seeds.

Since seed coating with neonicotinoid insecticides was introduced in the late 1990s, European beekeepers have reported severe colony losses in the period of corn sowing (spring). As a consequence, seed-coating neonicotinoid insecticides that are used worldwide on corn crops have been blamed for honeybee decline. In view of the currently increasing crop production, and also of corn as a renewable energy source, the correct use of these insecticides within sustainable agriculture is a cause of concern. In this paper, a probable--but so far underestimated--route of environmental exposure of honeybees to and intoxication with neonicotinoid insecticides, namely, the atmospheric emission of particulate matter containing the insecticide by drilling machines, has been quantitatively studied. Using optimized analytical procedures, quantitative measurements of both the emitted particulate and the consequent direct contamination of single bees approaching the drilling machine during the foraging activity have been determined. Experimental results show that the environmental release of particles containing neonicotinoids can produce high exposure levels for bees, with lethal effects compatible with colony losses phenomena observed by beekeepers.

UHPLC-DAD method for the determination of neonicotinoid insecticides in single bees and its relevance in honeybee colony loss investigations.

In the understanding of colony loss phenomena, a worldwide crisis of honeybee colonies which has serious consequences for both apiculture and bee-pollination-dependent farm production, analytical chemistry can play an important role. For instance, rapid and accurate analytical procedures are currently required to better assess the effects of neonicotinoid insecticides on honeybee health. Since their introduction in agriculture, neonicotinoid insecticides have been blamed for being highly toxic to honeybees, possibly at the nanogram per bee level or lower. As a consequence, most of the analytical methods recently optimized have focused on the analysis of ultratraces of neonicotinoids using liquid chromatography–mass spectrometry techniques to study the effects of sublethal doses. However, recent evidences on two novel routes—seedling guttations and seed coating particulate, both associated with corn crops—that may expose honeybees to huge amounts of neonicotinoids in the field, with instantly lethal effects, suggest that selected procedures need optimizing. In the present work, a simplified ultra-high-performance liquid chromatography–diode-array detection method for the determination of neonicotinoids in single bees has been optimized and validated. The method ensures good selectivity, good accuracy, and adequate detection limits, which make it suitable for the purpose, while maintaining its ability to evaluate exposure variability of individual bees. It has been successfully applied to the analysis of bees in free flight over an experimental sowing field, with the bees therefore being exposed to seed coating particulate released by the pneumatic drilling machine.

Perspective. Analytical validation of a general protocol for the preparation of dose-controlled solutions in aluminium toxicology

Aluminium(III) solutions suitable for careful toxicological investigation both in vivo and in vitro, are prepared from AlCl3·6H2O and from neutral metal complexes, Al(lactate)3, Al2(citrate)2(H2O)6, Al(acetylacetonate)3 and Al(maltolate)3, by dissolving the pure compounds in TRIS-HCl buffer solutions. The metal concentrations in the supernatant liquids are determined spectrophotometrically under reproducible conditions. Al(acetylacetonate)3 and Al(maltolate)3 are detected as molecular entities by using 1H NMR spectroscopy down to concentrations of 200 and 100 µmol l–1, respectively.

A pH-stat study of the reaction of some transition metal cations with disodium ethylenedinitrilotetraacetate (EDTA) and its analytical application

The pH-stat titration technique is an autonomous and very powerful tool for performing and monitoring chelatometric titrations of metal cations with great accuracy, poorly known, however, and seldom exploited. Based on measurement of the amount of strong base required to keep the pH of the test solution at a selected value during stepwise known additions of ethylenedinitrilotetraacetate (EDTA), it requires a glass electrode as the only sensor and is easily implemented on potentiometric titrators. It was introduced a quarter of century ago on an empirical basis for a very peculiar purpose (determination of calcium in diary products), but only very recently it was generalised and its fundamentals were thoroughly examined. In this work, pH-static titrations of some transition metal cations of analytical relevance (Co(2+), Cu(2+), Mn(2+), Zn(2+)) were thoroughly investigated in the acid pH range between 2.3 and 5 or 7 (the highest pH depending on the metal hydroxide or carbonate solubility). The results at higher acidity showed unsuspected properties of such chelation reactions. At moderately acid pH (generally >/=4), indeed, pH-static titrations yield results of high precision and accuracy. On decreasing pH, however, the reaction stoichiomety deviates more and more from the 1:1 ratio between chelating agent and cation, seemingly because of formation of binuclear complexes, an occurrence very seldom mentioned in the current literature. The optimal titration conditions for each metal are defined, and directions for establishing a laboratory protocol for quantitative determinations are given.

pH-stat techniques in titrimetric analysis: IV. pH-stat monitoring of chelatometric titrations

Abstract The theory of pH-stat chelatometric titrations recently developed [Anal. Chim. Acta 456 (2002) 313] is experimentally substantiated here. The titrations of four representative doubly charged cations having different behaviour (copper, zinc, calcium, magnesium) are taken as examples. Copper is titratable between pH 3 and 5, zinc between 3 and 6, calcium between 6 and 10, and magnesium between 7 and 10. The shapes of the titration plots agree well with the theory, accounting for simultaneous equilibria involving proton exchange. The technique yields accurate and precise results, which compare favourably with those of other instrumental techniques, in particular photometric titrations.

pH-Static Techniques in Volumetric Analysis I.

The pH-static option available in many potentiometric titrators can be exploited for acid-base titrations. The procedure consists of continuous or stepwise addition of the titrand solution to a suitable supporting solution (containing an inert electrolyte and, if necessary, a small concentration of buffer), and simultaneous addition of titrant to keep the measured pH at an appropriate constant value. Titrations of moderately concentrated strong and weak acids and bases are theoretically investigated. The criteria of choice of the experimental parameters, particularly of operating pH, ionic strength and buffer power of the measured solution, are discussed. The way these parameters affect the accuracy and the precision of the results is examined. It is inferred that pH-static titrations can be competitive with traditional titration procedures, particularly for the determination of the effective strength of secondary standard solutions of strong bases. Moreover, they can be used straightforwardly for the determination of acidity constants.