An area of discolored water 50 m wide and 30 m long was found in September 2017 close to the dam of the Irkutsk hydroelectric power station. Water from this spot was sampled for investigation in the present study. Microscopic analysis revealed that the suspended matter in the sample was composed of clumps of filaments, vegetative cells, akinetes and heterocysts that formed short filaments and solitary cells. This matter was found to consist of partially degraded cells of the cyanobacterium Dolichospermum lemmermannii. Nucleotide sequencing of DNA isolated from the biomass revealed the presence of the sxtA gene which is involved in the synthesis of saxitoxin. Water from the polluted area contained 600 ± 100 μg L−1 saxitoxin as measured by HPLC-MS with pre-column modification of the toxin with 2,4-dinitrophenylhydrazine. Immunoassay analysis (ELISA) showed a concentration of saxitoxins in the water of 2900 ± 900 μg L−1. Hydrochemical and microbiological analyses suggested the contaminated area appeared as a result of a D. lemmermannii bloom, followed by its decay and release of saxitoxin and nutrients. The present paper describes the results of a case study. Better understanding of the phenomenon will depend on the possibility to perform implementation of a large-scale monitoring program.

The regioselectivity of the conjugate nucleophilic addition of amines to vicinal di-acceptor-substituted alkenes has been studied. A set of results obtained with standard primary and secondary amines gives some clues on the relative acceptor character of classical electron-withdrawing groups (EWG). We have shown in addition that computed inverse local nucleophilicity index can be used to predict the regioselectivity of the nucleophilic attack.

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The halogenation of electron‐deficient vicinal substituted alkenes leads mainly to the mixture of regio‐ and stereoisomers of monohalogenated derivatives. Their ratio depends on the stability of the intermediate anionic complex and is determined by properties of both electron‐withdrawing groups.

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