The use of native mosses to monitor fluorine levels—and associated temporal variations—in the vicinity of an aluminium smelter

This paper describes an assessment of environmental exposure to fluorine in the surroundings of an aluminium smelter, carried out by measuring fluorine concentrations in the tissues of mosses growing in the area. Forty-two samples were collected from within a 3300 m of radius of the smelter on two different occasions. Samples of either Hypnum cupressiforme Hedw. or Scleropodium purum (Hedw.) Limpr. were collected at each point, depending on which was the most abundant. The fluorine contents in the samples varied from <10 μg g−1 F (the limit of quantification of the analytical technique used) to 154 μg g−1 F. To analyse the spatial pattern of fluorine accumulation in the mosses, response surfaces were adjusted to the data using the geographic coordinates of the sampling points as independent variables. Details are given of the process used to select the best surface from among the many candidates available. The graphical and mathematical analyses of the surfaces allowed description of the effect of the distance from the smelter on fluorine concentration and of the spatial anisotropy, i.e. the existence of directions along which fluorine deposition is enhanced. Fluorine concentration decreased exponentially over all the study area, therefore the impact of the smelter decreased greatly within a short distance. The surfaces also allowed detection of differences between sampling times, in terms of the prevailing direction of pollutant movement, as well as differences in the rates of decrease in concentration with distance from the plant. Finally, it is discussed how the particular characteristics of the source of the pollutant affect its dispersal, and how some sampling difficulties encountered affected the results obtained.