Comparison and evaluation of pesticide monitoring programs using a process-based mixture model.

A number of European countries run large-scale pesticide monitoring schemes in watersheds aimed at identifying and evaluating the presence of pesticide residues in the environment. These schemes provide national and regional scale assessments of pesticide concentrations within the context of environmental quality assessment, aiming to ensure some degree of ecological protection. The present study is aimed at evaluating the joint effects of the pesticide mixtures detected in monitoring programs, using a process-based mixture model that was parameterized for Daphnia magna. In total, over 15 000 samples containing over 1 million individual measurements were evaluated for effects. It was found that there are only a small number of places where one can expect to have effects on daphnids, based on measured concentrations. The most polluted samples would cause extinction of a daphnid population within only 30 h. The results show that effects are mostly triggered by a limited number of pesticide residues at locations with high emissions. It was also shown that the analytical detection limits are basically too high to exclude mixture effects. So, despite all the effort that is put into chemical monitoring programs, it remains a challenge to make statements on whether or not the environment is protected. Recommendations are offered for a different setup of monitoring programs to improve this situation. Environ Toxicol Chem 2016;35:3113-3123. © 2016 SETAC.

Mechanism for the reductive activation of diaziquone.

In order to understand the redox properties of diaziquone (AZQ) and the reductive alkylation role of its one-electron reduced free radical anion AZQ- in biological systems, we investigated the electrochemical and structural properties of AZQ and its reduced species by cyclic voltammetry, controlled potential electrolysis, optical absorbance spectroscopy and 1H NMR. This study was carried out in aqueous media as well as in Me2SO. In aqueous media AZQ can be reduced by 2 electrons to the dianion AZQ2- which is oxidized back to AZQ- and AZQ. In Me2SO, 1 - e- reduction or oxidation steps are possible. This allowed the characterization of AZQ and its 1 or 2 - e- reduced species by UV-visible absorbance spectroscopy. The redox properties of the aziridine rings were observed by cycle voltammetry. Using 1H NMR, it was possible to follow the structural dependence of AZQ on the nature of the medium. Protonation of the aziridine rings at low pH may facilitate the opening of the ring leading to the carbonium ion, the required species for alkylation. Cyclic voltammetry data indicate that reduction of the quinone facilitates the aziridine ring opening.

Method for the quantitation and characterization of the cholinergic neurotoxin, monoethylcholine mustard aziridinium ion (AF64A).

Monoethylcholine aziridinium ion (AF64A), which is generated from the precursor, acetylcholine mustard hydrochloride, exerts selective neurotoxic effects against brain cholinergic neurons when injected intracerebrally. Conditions associated with optimal generation of AF64A were examined. The results indicate that hydrolysis and cyclization of the precursor are optimal at 25 degrees C with the former occurring at pH 9.0 and the latter at pH 7.3. The aziridinium ion is best stabilized at pH 7.3 at 4 degrees C.

Determination of carboquone in plasma and ascites by high performance liquid chromatography after intravenous and intraperitoneal administration in man.

A new method for the determination of carboquone (CQ) in human plasma and ascites by high performance liquid chromatography has been developed. The method is sensitive enough to determine levels as low as 1.0 ng per 1.0 ml of plasma or ascites. The average recovery of CQ from these samples was 89.3 +/- 0.9% (n = 5, mean +/- SD). The method consists of 2 steps, 1) extracting CQ from human body fluids with chloroform and 2) quantization of CQ by chromatography using a mu-Bondapak C18 column, monitored at 340 nm, 2,5-Diethyleneimino-3,6-dimethylbenzoquinone was used as the internal standard. Using this analytical method, the concentration-time profiles of CQ in human body fluids after intravenous and intraperitoneal administrations were obtained. It was recognized that intraperitoneal administration of CQ was advantagenous for the treatment of peritonitis carcinomatosa since an effective concentration could be maintained in ascites for about 6 hr.

2,5-Diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone I: Kinetics in aqueous solutions by high-performance liquid chromatography.

The application of a rapid, selective, and sensitive reversed-phase high-performance liquid chromatographic method to the analysis of 2,5-diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone (I) and its degradation products is described. The method was used to study the kinetics of degradation of I over pharmaceutically useful pH ranges. The overall reaction rate followed pseudo-first-order kinetics. The pH-rate profile demonstrated optimal stability between pH 6.0 and 6.5. The degradation behavior suggests the existence of multiple pathways. The temperature dependence of th disappearance of I also was evaluated from the regression equation derived from the Arrhenius plot.

2,5-Diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone II: Isolation and characterization of degradation products.

A direct high-performance liquid chromatographic (HPLC) method was applied to monitor 2,5-diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone (I) and its degradation products in pharmaceutical vehicles at 25 +/- 0.1 degrees. At the optimal pH for stability of I, an increase in buffer concentration [phosphate and tris(hydroxymethyl)-aminomethane] or ionic strength accelerated degradation. The reaction rate in the solutions studied followed pseudo-first-order kinetics. Degradation products were characterized by mass spectrometry after isolation by semipreparative HPLC. Different degradation pathways prevailed in acidic and basic media. The acid-catalyzed reaction resulted in consecutive aziridine ring opening, while the base-catalyzed reaction led to nucleophilic displacement of thie aziridine ring(s).

Mass spectrometry as a technique for testing the purity of drugs for biological use: the case of new antitumor cyclophosphazenes.

Mass spectrometry has been used for testing the chemical purity of some new antitumor cyclophosphazene compounds. the spectrum of N3P3Az6 (code name MYKO 63)--which exhibits noticeable activity on murine P 388, L 1210 and B 16 tumors--appeared to be remarkably simple, as most of the fragmentations arose from successive losses of the aziridino radicals. Traces of the pentaziridinomonochloro impurity formed by an incomplete substitution of N3P3Cl6 chlorine atoms under aziridinolysis could be detected in an impure and toxic sample by spectral subtraction. Quantification of this impurity was performed by selected ion monitoring in the direct inlet mode of sample introduction. The mass spectra of other derivatives of this class of compounds are slightly more complex, since the decomposition pathways showed more intense H-transfers associated with the loss of substituents.

Rapid estimation of trace amounts of ethylenimine by high-pressure liquid chromatography.

A rapid procedure utilizing high-pressure liquid chromatography is described for determining trace quantities of ehtylenimine down to 0.01 ppm. The basis for the method is the quantitative reaction of ethyleneimine with the 1,2-naphthoquinone-4-sulphonate ion (Folin's reagent) to give 4-(1-aziridinyl)-1,2-naphthoquinone. Compared with the spectrophotometric procedure, this method provides a high degree of specificity and sensitivity. The method has been employed to determine ethylenimine in the pyrolysis products of polyethylenimine.