The Seleznevka river is a common water body between Russia and Finland. In Finland, the river is called Rakkolanjoki (fin. Rakkolanjoki). In Russia, the Seleznevka flows through the territory of the Vyborgsky district of the Leningrad region, in Finland – through the territory of Lappeenranta. Length is 53 km (across Russian territory – 20 km). The source of the river is located near the city of Lappeenranta, and its estuary is in the Vyborg bay of Finland bay. In addition to the fact that the Seleznevka River is a common water body between Russia and Finland, this river receives water from the treatment facilities of the city of Lappeenranta. Thus, the Seleznevka river became an object for research.

On November 4, water samples were taken from the Seleznevka River. Sampling was carried out at three points. The first point was after all settlements. But before the place where the Malaya Lipovka river flows into the Seleznevka river. The second point was before the village of Luzhayka. The third point was in the village of Kutuzovo. The village of Kutuzovo is located in a 5-kilometer zone before the border area between the countries. Therefore, the third point is the closest one to the border where water can be taken.

During sampling, the coordinates of the sampling site, air and water temperatures, weather conditions, and sampling time were recorded. The weather was changing during the day from sunny to rainy. After taking and preserving the samples, glass and polyethylene bottles were placed in a portable refrigerator to maintain the temperature of 4 ° C.

The next day, the samples were delivered to the Institute of Chemistry of St. Petersburg State University (SPbSU) for analysis.