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Moss and metals

Croppet. Originalfoto: Sigmund Lie

From the NILU annual report 2015: Air pollution knows no borders. Particles emitted from sources far from Norway are transported through the atmosphere and deposited in Norwegian mountains and forests. Moss have proven to be especially useful when scientists want to map the atmospheric
deposition of heavy metals in the environment.

By Sonja Grossberndt

Hilde Thelle Uggerud
Seniorforsker Hilde Uggerud analyserer mose for å kartlegge tungmetaller i norsk natur. Foto: Ingar Næss

Hilde Uggerud, senior scientist in NILU’s Department of Environmental Chemistry, has for many years collaborated with Professor Eiliv Steinnes from the Norwegian University of science and Technology (NTNU), analysing floor moss (Hylocomium splendens; see picture). Steinnes, who first started surveying moss in Norway, has every 5 years since 1977 collected floor moss from up to 464 different locations all over the country. As of today, NILU performs the moss survey on commission from the Norwegian Environment Agency.

Natural air samplers

– Floor moss, like all moss, does not take up nutrients through roots. Nutrition is obtained through the surface of the plant and is therefore a good indicator of what is in the air and precipitation, explains Uggerud. – Moss has a special ability to bind trace elements, such as metals, radionuclides and certain organic pollutants that may accompany the rain and air. It thus acts as a kind of passive sampler. In the laboratory, we can use a variety of analytical methods to determine which substances the moss has absorbed.

The advantage of floor moss is that it grows in all parts of Norway. With more than 200 sampling sites spread throughout mainland Norway, the moss survey effectively maps the geographical deposition pattern of heavy metals from the atmosphere. This makes the moss survey a good supplement to the national monitoring of air and precipitation, which includes heavy metal samples taken from a few selected monitoring stations.

Clear trends

The moss shows several interesting trends. Deposition of metals such as lead, zinc, cadmium and vanadium is higher in the south than in the north part of the country. The reason is that southern Norway is more influenced by transboundary air pollution from Europe. In general, the data show a reduction in the contribution from long-range atmospheric deposition of these metals during the moss survey period.

This is most obvious for lead, for which the concentration in moss has dropped significantly after the phasing out of leaded gasoline in the 1990s. For metals such as nickel, copper and chromium, local sources contribute more to the concentration in moss than transboundary air pollution. An example of this is found in the high north of Norway, where emissions from the Russian smelter in Nikel has caused an increase in deposition of copper and nickel in eastern parts of Finnmark.

Industrial companies contribute

Working with the moss survey, scientists have found that in some cases it is possible to identify how local point sources contribute to the regional fallout pattern. Thus, they have carried out an additional investigation since 2000, collecting moss around various companies where they know or can assume emissions of heavy metal occur. The Norwegian Environment Agency invites companies to participate in the survey, which is funded by the companies themselves. The industry shows great interest in the survey, and 22 companies participated in 2015.

The values measured in moss from areas surrounding industrial companies are compared with values from the nationwide moss survey. In general, the most polluted industrial estates are located in Mo i Rana and Odda. The results also indicate how well the air pollution-reducing measures work in the different companies.

A European map

Kart som viser gjennomsnittlig konsentrasjon av krom i mose
Mean chromium concentration in mosses per EMEP grid cell in 2010 (left) and expressed as percentage of the values in 2005 (right); values below 100% represent a decline, values above 100% represent an increase since 2005. Source: Harmens et.al., Heavy metals and nitrogen in mosses: spatial patterns in 2010/2011 and long-term temporal trends in Europe.

– Results from the moss surveys are of international importance, says Uggerud. All data are reported centrally to ICP Vegetation, an international monitoring program under the United Nations Economic Commission for Europe (UNECE). The partnership started in 1990, with more than 20 countries participating. The common moss survey helps map the pollution situation across Europe. So far, the moss results have confirmed the results from the air measurements.

The surveys show a reduction of heavy metal concentrations in moss since 1990. Lead concentrations have decreased the most, while the concentration of copper shows the lowest decline. The lowest concentrations of heavy metals in moss are found in Northern Europe, low to moderate amounts in Western and Central Europe, while the highest concentrations are reported from Southern and Eastern Europe. The results are used internationally, for example, in modeling contamination.

In 2015, yet another survey was completed. Now, the scientists are working on analysing and interpreting the data. The results will be made public in a report to the Norwegian Environment Agency and participating companies in summer 2016.