CHANGES IN ATMOSPHERIC DEPOSITION RATES OF HEAVY METALS IN SWEDEN: A Summary of Nationwide Swedish Surveys in 1968/70 – 1995
The Swedish nationwide surveys of atmospheric heavy metal deposition in 1968/70 – 1995 using bryophytes (carpet-forming mosses) as monitors are reviewed. Considered are cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), mercury (Hg), nickel (Ni), vanadium (V), and zinc (Zn). The close agreement between data obtained with deposition (precipitation) collectors and moss carpet analysis is documented briefly, as well as measures of quality control and assessment of reproducibility. Since 1968/70, the deposition rate of the heavy metals considered has declined gradually and evenly, particularly in the southern parts of the country, reflecting an improvement of general air quality due to decreasing dust emission from mainly industry and fossil fuel combustion in northern and western Europe. By far the greatest absolute decrease in deposition rate was measured in Fe, which is a main constituent of most man-generated dust particles. However, the greatest per cent decreases in deposition rates were measured for Pb. The Pb concentration of moss carpets in Sweden as a whole in 1995 was only 11% of the value in 1968/70. Corresponding figures for Fe was 20%, Cd 24%, Ni 28%, Hg 31%, V 43%, Zn 51%, and Cu 52%. For Zn the current deposition rate seems to approach a ‘natural’ baseline, whereas deposition of the other seven elements are still decreasing according to the surveys of 1990 and 1995.