Radioactivity in surface water

Analyzing radioactive materials in surface waters provides information on their time behaviour. Samples taken from different bodies of water indicate the geographic variation of radionuclides.

Starting from 2024, the Kokemäenjoki and Oulujoki samples will be examined four times a year, and the Kymijoki and Kemijoki samples will be examined once a year, in spring or in autumn (Figure 6.1). In 2024, annual samples were taken in the spring. Strontium was no longer analysed in the 2024 samples.

The uneven regional distribution of Chernobyl fallout is still reflected in surface water results for 137Cs. Unlike Chernobyl fallout, the fallout from nuclear weapon tests was nearly evenly distributed in Finland, and its traces are still observed in the river water from northern Finland. Before the fallout from Chernobyl, concentrations of 137Cs were fairly even, but after 1986, the situation changed and caesium concentrations in surface water increased, but the concentrations have gradually fallen close to the situation before the Chernobyl accident. The highest concentrations of 137Cs are observed in samples in the Kymijoki catchment area, whose concentrations were approximately 3–10 orders higher than in surface water samples from other sources

The radioactivity levels of Cs-137 and Sr-90 in surface water samples in 2024 (Bq/m3)

River	Reference day	Cs-137 (Bq/m3)
Kymijoki	11.3.2024	11
	6.5.2024	11
	8.8.2024	13
	5.11.2024	12
Kokemäenjoki	15.5.2024	4,0
Oulujoki	27.3.2024	2,5
	29.5.2024	8,9
	9.9.2024	2,4
	4.11.2024	1,9
Kemijoki	23.4.2024	2,0

The radioactivity levels of Cs-137 and Sr-90 in surface water samples in 2023 (Bq/m3)

River	Reference day	Cs-137 (Bq/m3)	Sr-90 (Bq/m3)
Kymijoki	9.10.2023	14,2	4,3
Kokemäenjoki	18.9.2023	4,5	3,9
Oulujoki	26.9.2023	2,7	2,5
Kemijoki	10.10.2023	1,2	2,1

 

The radioactivity levels of Cs-137 and Sr-90 in surface water samples in 2022 (Bq/m3)

The radioactivity levels of Cs-137 and Sr-90 in surface water samples in 2021 (Bq/m3)