The ICP Vegetation is an international research programme investigating the impacts of air pollutants on crops and (semi-) natural vegetation. The programme 
focuses on two air pollution problems: impacts of ozone pollution on vegetation and the atmospheric deposition of heavy metals to vegetation. In addition, 
the ICP Vegetation is taking into consideration impacts of pollutant mixtures (e.g. ozone and nitrogen), consequences for biodiversity and the modifying 
influence of climate change on the impacts of air pollutants on vegetation. 
            

Heavy metals    
    
The moss survey provides an effective and cheap method for monitoring spatial and temporal trends in heavy metal pollution across Europe.    
    
There is an east/west decrease in heavy metal concentrations in mosses, related in particular to industry.    
    
Transboundary transport accounts for elevated concentrations of heavy metals in areas without emission sources, such as lead in southern Scandinavia. 
In those areas, high correlations were found between the lead concentration in mosses and the total lead deposition modelled by EMEP.    
    
Between 1990 and 2000, a dramatic decline in the concentrations of lead (57%) and cadmium (42%) in mosses was found across Europe, with a smaller decline being 
observed for vanadium (32%), zinc (19%) and copper (16%). For arsenic, chromium, iron, mercury and nickel the concentration in mosses did not change significantly 
with time. 
            

Human activities such as fuel combustion, manufacturing industries or metal production and processing are sources of anthropogenic emissions of  
heavy metals in the atmosphere. Heavy metals in the atmosphere may travel over large distance before being redeposited on soils. Conventional  
measurements of heavy metal deposition are based on precipitation analysis. Measuring large areas therefore implies deploying large numbers of  
precipitation collectors with an associated long-term programme of sample collection and analysis. Alternatively, the technique of moss analysis  
provides a surrogate, time-integrated measure of metal deposition from the atmosphere into soils. This technique is easier, cheaper, less prone to  
contamination, and allows a much higher sampling density than conventional analysis. A biomonitoring network coordinated by the United Nations  
Economic Commission for Europe (UNECE) International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops (ICP  
Vegetation)1 provides data on the concentration of 10 heavy metals in mosses from about 7000 sites across Europe. The purpose of this monitoring  
programme is to provide information on the spatial and temporal distribution of heavy metals in Europe, identify the main polluted areas and develop  
the understanding of long range transboundary pollution. 
 
A European team of scientists has recently analysed the monitoring data of 10 heavy metals across Europe between 1990 and 2000. The metals are  
arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, vanadium and zinc. Results were compared with trends in the modelled total  
deposition or the anthropogenic emission of metals reported by the UNECE Cooperative Programme for Monitoring and Evaluation of the Long-range  
Transmission of Air Pollutants in Europe (EMEP). The main results are as follows: 
 
*Whereas the arsenic, cadmium, copper, lead, vanadium, and zinc concentration in mosses decreased significantly between 1990 and 2000, the  
decreases for chromium, iron, mercury and nickel were not significant. Country-specific temporal trends were observed for all the metals. 
*The temporal trends for cadmium (-42%), lead (-57%) and mercury (-8% between 1995 and 2000) were similar to the ones reported by EMEP  
regarding modelled total deposition of cadmium (-45%), lead (-52%) and mercury (-8%) in Europe. 
*Currently, no data is available for the modelled deposition of other heavy metals in Europe. However, decreases in the anthropogenic emissions of  
arsenic, copper, chromium, nickel and zinc between 1990 and 2000 have been reported by the EMEP programme. 
*On a smaller scale (regions, provinces, etc…), trends can be different due to local conditions. 
 
The authors conclude that mosses provide a cheap and effective method for monitoring temporal trends in heavy metal pollution in Europe. Reductions  
in the anthropogenic emissions of heavy metals between 1990 and 2000 have resulted in a significant reduction of the accumulation of arsenic,  
cadmium, copper, lead, vanadium and zinc in mosses. Lastly, the observed temporal trends in the concentration of heavy metals in mosses were not  
only metal-specific but also country-specific.