Pollutants in lake sediments

Last updated 5 August 2016

Pollutant levels in lake sediments are generally low in the Arctic. They are classified as insignificantly to moderately polluted. Sediment cores from Ellasjøen, a lake on Bjørnøya, show an increase in PCBs and DDT from the 1930s to the 1970s, followed by a reduction. The brominated flame retardants, PBDEs and HBCDs, show an increase from 1940 to 2000. No reduction is seen for these, but recent data are lacking.

Status and trend

Sediment is very suitable for monitoring the trend in environmental pollutants over time. A single sediment core contains the history of the environment because the age increases down the core. If the core is divided into slices and the age of the slices is determined, the trend in the amount of pollutants in the lake can be reconstructed from a single core. The figures showing the trend in PCBs, DDT, HBCDs and PBDEs from Ellasjøen on Bjørnøya are based on one sediment core sample. We see that the concentration of PCBs and DDT began to increase in the 1930s and rose until the mid-1970s, when they began to decline. Based on what we know about the manufacture and use of PCBs, the increase in the PCB concentration started a bit earlier. The reason for this is probably that some material from more recent layers contaminates the sediment further down the core when the core is pressed up through the sampling tube.

The trends of PCBs and DDT in the sediment core agree very well with the industrial history of PCBs and DDT. In Norway and many other western countries, DDT was regulated from 1969 and the early-1970s, and new uses of PCBs were banned in 1980. PCBs are still found in old building materials and some other products in Norway, and to prevent them escaping into the environment they must be delivered as hazardous waste when they become disused. The content of PCBs in the core indicates that the sediment had background concentrations (class 1) of PCBs until the 1930s, after which the content rose to class 3 – moderately polluted. The concentrations of DDT are low and correspond to class 2 – good environmental state.

The amount of the brominated flame retardants, PBDEs and HBCDs, increased from 1945 until 2001, which is the last measurement point for this series. From what we know about their manufacture and use, the rise in the PBDE and HBCD concentrations starts somewhat earlier. The reason for this is probably that some material from more recent layers contaminates the sediment further down the core when the core is pressed up through the sampling tube. The regulation of PBDE flame retardants began at the beginning of this century and the mixtures, penta- and octa-BDE, were included in the Stockholm Convention in 2009. The classification of these brominated flame retardants is incomplete. 

The concentration of mercury (Hg) in the sediment is classified as class 2 – good. We see that there has been a smooth, but small, rise throughout the period from 1875 to 2001. The use of mercury is now subject to stringent restrictions, but mercury escapes from the metallurgical industry and the combustion of fossil fuels. The supply of mercury and other pollutants to Bjørnøya is mainly through long-distance transport and the sources are therefore global. Emissions of mercury in Norway have been reduced by 66% during 1995–2013. However, they are still comparatively large in relation to the targets set by Norwegian authorities. Batteries are currently the greatest source of mercury emissions in Norway. Because mercury has many small and diffuse sources ranging from combustion (natural: forest fires, volcanic activity and evaporation from the sea; and anthropogenic: industry, combustion of waste, oil, coal and gas), it takes a long time to overwin the mercury emissions.

Organic pollutants are internationally regulated through the Stockholm Convention and mercury through the Minamata Convention.

Causal factors

The declining concentrations of PCBs and DDT in lake sediments from Bjørnøya are a result of international regulation of the manufacture, use and emission of organic pollutants. When the sampling took place, the relatively recently regulated or non-regulated organic pollutants (i.e. the brominated flame retardants, PBDEs and HBCDs) did not show the same declining trends as the old, regulated organic pollutants. However, it is reasonable to assume that the concentration of these pollutants, too, is now declining in lake sediments.

Mercury (Hg) is regulated through the Minamata Convention. Regulations of the amounts of mercury in oil products and cleansing of gases from industry, coal-fired power stations and ships mean that mercury has been reduced in North America and Europe since the 1990s, whereas the emissions in Asia have risen greatly, mainly due to increased burning of coal in coal-fired power stations. Even so, recent data from mainland Norway indicate rising mercury concentrations in lakes. However, it is uncertain whether this trend also applies to lakes in Svalbard.

Consequences

The lake sediments in Svalbard have enhanced concentrations of anthropogenic pollutants (PCBs, DDT, brominated flame retardants and mercury). They are classified from insignificantly (background) to moderately affected. Polycyclic aromatic hydrocarbons (PAHs) are not included in this assessment. The sediments may be affected by PAHs because much of the bedrock in Svalbard contains coal.

About the monitoring

Sediment is very suitable for monitoring the trend in environmental pollutants over time. A single sediment core contains the history of the environment because the age increases down the core. If the core is divided into slices and the age of the slices is determined, the trend in the amount of pollutants in the lake can be reconstructed from a single core. The lake sediment is thus an historical archive waiting there, ready for reconstruction if the need should arise.

Further reading