Metals in lakes

Published by the Norwegian Environment Agency Lag rapport Les på norsk

Lake sediments in large parts of Southern Norway are polluted by lead, mercury and cadmium. The overall human and environmental risk caused by these metals are considered low, however due to the detection of high concentrations of mercury the Norwegian Food Safety Authority has issued a nationwide advice against the consumption of some fresh water fish.

Southern parts of Norway most polluted

Metals such as lead, mercury and cadmium are transported to Norwegian lakes with air and precipitation. With time the metals will sink to the bottom of the lake where they can be found in the sediment layers. These sediments are therefore an important historical archive which reflects trends in emissions at different time periods.

A nationwide survey of sediments in 274 lakes has documented that lake sediments are polluted by lead, mercury and cadmium. This statement is based on a comparison of metal levels in sediment layers dated before the Industrial Revolution and sediment from the present time. 

Decline in lead pollution, levels of mercury unchanged

Lead levels in lake sediments have declined during the last decades but is still the metal found in highest concentrations. When it comes to mercury no change has been detected since 1995.

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Higher pollution levels in the South

Levels of most pollutants are generally lower in northern parts of Norway. However, several lakes in Sør-Varanger, close to the Russian border, are significantly polluted by copper and nickel.

Small threat to humans and animals

Since the levels of metals in lake sediments are comparatively low, the risk of harmful substances entering the food chain is small. Humans and animals are therefore not in immediate danger. However, one exception is mercury, which is able to transform to methyl mercury and then can be taken up by organisms.

Advice against consumption

Due to the detection of high concentrations of mercury the Norwegian Food Safety Authority has issued a nationwide advice against the consumption of fresh water fish. The warning concerns pike and perch larger than 25 cm. and big trout and char ( >1 kg). Pregnant women and breastfeeding mothers should avoid eating such fish. Others should not eat such fish more than once a month.

Gradual reduction of emissions

Emissions of metals to the atmosphere take place when we burn coal and oil or incinerate waste. Manufacturing of iron and cement is another pollution source. Anthropogenic emissions of metals were generally insignificant before the Industrial Revolution, although lead emissions from German mining activities during the 18th century may have affected lakes in the southern parts of Norway.

Emissions of metals increased dramatically after the Industrial Revolution, especially from the Second World War and up to the 1970s. In the past 20-30 years European manufacturers have installed fume treatment facilities, and this has led to a gradual decrease in air pollution levels.

Long-range pollution the most important source

Long-range air pollution is the main reason for the pollution of in lake sediments in Norway. Most long-range pollution is deposited in coastal areas and in Southern Norway, which is also where the sediments are most polluted. High levels of copper, nickel, cobalt and chromium pollution have also been registered in localities close to smelters and metallurgical industry.

Zinc and cadmium levels are highest in South and Southeastern Norway. This is probably a result of pollution from industrial activity in Eastern Europe. Emissions from local manufacturing have raised pollution levels in Arendal and Karmøy. Several lakes in Sør-Varanger in Finnmark are significantly polluted by copper and nickel emitted from Russian smelters.

Use of unleaded petrol has improved the situation

Measures to reduce the use of leaded petrol has led to significant reductions in emissions. Road transport is the main source of lead pollution in Europe. Even though more and more unleaded petrol is being used, all types of petrol still contain small amounts of lead, which is naturally present in crude oil. Nevertheless, lead levels have decreased over the last twenty years.

In recent decades the installation of fume treatment facilities has led to a gradual decrease in metal pollution to air.