Despite the good nutritional properties of fish, the levels of harmful substances still need to be considered. Overall, the situation has improved significantly since the turn of the millennium.

Although many harmful substances accumulate in fish, not all such accumulations cause restrictions on fish use. Nor do they have a significant impact on fish health. However, fish will transfer toxic substances up the food chain, even to humans. The older the fish, the more harmful substances they have been able to collect over their lifetime.

The level of environmental toxins in fish is constantly monitored

In 2018, The Prime Minister's Office published a bulletin on the levels of environmental toxins in domestic wild fish. According to the bulletin, the concentrations of ecotoxins in Finnish fish have fallen sharply during the 2000s. Finland has an abundance of wild fish whose food use could be increased in complete safety and to achieve public health benefits.

However, the bulletin also stated that the levels of environmental toxins in salmon and herring are still so high that it is as yet impossible to export them for food. Nevertheless, the reduction in these toxin levels has been significant, particularly for herring.

The herring and sprat being used for animal and fish feed must continue to be cleansed of environmental toxins.

Some heavy metals are still found in considerable quantities in certain fish species

Measurements have shown that certain chemical compounds were still found in significant concentrations in some fish species. The heavy metals and environmental toxins found were:

• Dioxins and PCBs - sea salmon, river lamprey
• PBDEs - sea salmon, river lamprey
• PFAS - sea smelt, in the roe of vendace
• Mercury - pike and zander in lakes
• Cadmium - river lamprey
• Arsenic - herring, sprat, river lamprey, sea salmon

The concentrations of organic ecotoxins in fish have decreased between 2002 and 2016. By contrast, heavy metal concentrations have mainly increased.