Scientific registration n 0 : 1893 Symposium n 0 : 2 Presentation: poster Multi-purpose Soil Geochemical Mapping of Portugal: preliminary results Différentes applications de la cartographie géochimique des sols du Portugal : premiers résultats INÁCIO Manuela, FERREIRA António, FERREIRA Luís, ALMEIDA Luís, PEREIRA Virgínia, PINTO Manuel Departamento de Geociências, Universidade de Aveiro, 3800 Aveiro, Portugal. 1. INTRODUCTION The obtention of geochemical data documenting the present composition of the surface environment is now recognized as a priority in many countries. A project aiming at producing low density baseline data for the whole continental area of Portugal, taking both active stream sediment and topsoil as the sampling media, is under way at the University of Aveiro. It follows recommendations of the IGCP Project 29 International Geochemical Mapping (Darnley and Garrett, 1990; Darnley et al., 199) and received support from A. Björklund, former leader of the technical committee on field methods of that international project. The data now presented are preliminary results concerning the baseline levels of 12 trace elements in soils of Portugal. 2. METHODS The data were obtained in a consistent way from 1 sites at a sampling density of 1 site/170 km 2. The sampling sites were selected to represent natural soils, therefore locations obviously affected by pollution (near factories, heavy traffic roads, mines) and arable soils were avoided. At each site a composite of topsoil (0-20cm) subsamples was collected; duplicates were taken every 10 sites. The samples were dried at 3-40 0 C and sieved through a 80# plastic screen. Representative 0.00g subsamples were extracted with acqua regia (3-1-2 HCl-HNO 3 - H 2 O) at 9 0 C and the extracts were analysed for 31 elements by ICP-AES. Randomization of samples was performed prior to analysis in order to remove any systematic relationship between order of analysis and geographic location. The elements analysed were the 9 major - Al, Ca, Fe, K, Mg, Mn, Na, P, Ti - and 22 trace elements - Ag, As, Au, B, Ba, Bi, Cd, Co, Cr, Cu, La, Mo, Ni, Pb, Sb, Sr, Th, Tl, U, V, W and Zn. The analytical results for Ag, Au, B, Bi, Cd, Mo, Sb,Tl, U and W were refused because they contained more than 20% values below the limit of detection. The accuracy and precision for the remaining elements was acceptable. 3. RESULTS The observed range, median, geometric mean, and the expected range for the 12 trace elements selected are shown in table 1. The expected range or baseline levels were calculated after Tidball and Ebens (1976): 1
ER= GM/GD 2 - GMxGD 2 where GM is the geometric mean and GD is the geometric deviation. Table 1. Concentrations (mg kg -1 ) of trace elements in topsoils of Portugal. Element Observed range Median Geometric mean Expected range As 1-324 9 8 1-73 Ba 6-422 6 3 13-218 Co 1-9 7 1-49 Cr 2-243 22 18 3-99 Cu 1-24 16 14 2-91 La 1-1 2 24 7-87 Ni 1-39 16 14 2-104 Pb 3-8 21 21 7-6 Sr 2-217 11 12 3-7 Th 1-87 4 1-22 V 4-192 28 26 6-10 Zn -678 3 4 10-203 Co, Cu, Ni, Pb and Zn levels are not very different from the median contents and ranges reported in the literature and compiled by Adriano (1986) but the figures for As are high and those for Ba, Sr, Cr and V are low to very low. Geochemical maps displaying the spatial distribution of these elements were prepared. The geochemical patterns are generally well correlated to the solid geology as exemplified by Co and Th distributions. Co (figure 1) is very low in soils developed from sandstones and limestones, the highest contents being found in soils underlain by schists of Carboniferous and Devonian ages. The highest levels of Th (figure 2) are found in soils overlying Hercynian granitic rocks. As distribution (figure 3) is more difficult to explain at this scale; further investigation is necessary in order to recognize if the high to very high As contents in the north are natural levels or if they are caused by man-made sources of pollution. 4. CONCLUDING REMARKS Systematic baseline geochemical data are necessary to provide a sound basis both for environmental legislation and research. The first soil geochemical maps of Portugal based on consistent sampling and analysis have been presented. The analysis of many more elements, including all the priority pollutants, is planned for a near future, having as an ultimate goal the compilation of a geochemical atlas. References Adriano, D.C., 1986. Trace Elements in the Terrestrial Environment. Springer-Verlag. Darnley, A.G. and Garrett, R.G. (Eds.), 1990. International Geochemical Mapping. J. Geochemical Exploration, 49:1-20. Darnley, A.G., Björklund, A., Bolviken, B., Gustavsson, N., Koval, P.V.,Plant, J.A., Steenfelt, A., Tauchid, M., Xie, Xuejing, Garrett, R.G. and Hall, G.E.M., 199. A Global Geochemical Database for Environmental and Resource Management: 2
Recommendations for International Geochemical Mapping. Earth Sciences 19, UNESCO. Tidball, R.R. and Ebens, R.J., 1976. Regional geochemical baselines in soils of the Powder River Basin, Montana, Wyoming,. In R.B. Laudon (Ed.) Geology and energy resources of the Powder River Basin, Wyoming Geol. Assoc., 28th Ann. Field Conf. Guidebook, pp. 299-310. Key words: Geochemical database, Portugal, trace elements in soils, As, Ba, Co, Cr, Cu, La, Ni, Pb, Sr, Th, V, Zn. Mots clés : base de données géographiques, Portugal, éléments traces, sols, As, Ba, Co, Cr, Cu, La, Ni, Pb, Sr, Th, V, Zn. 3
Figure 1. Co distribution in topsoils of Portugal. Co mg/kg Percentile 32 98 27 9 22 90 1 7 9 0 4 2 1 100 km 4
Figure 2. Th distribution in topsoils of Portugal. Th mg/kg Percentile 87 31 98 19 9 14 90 7 7 4 0 2 2 1 100 km
Figure 3. As distribution in topsoils of Portugal. As mg/kg Percentile 324 74 98 2 9 33 90 18 7 9 0 3 2 2 100 km 6