The objective of the present work was to verify and compare the performance of different geochemical indices employed to identify the anthropogenic origin of selected heavy metals and other trace elements in soils. To that end, two background values, the upper continental crust and the metal content in the bed rock, were used and obtained from a forested basin of the western Pyrenees. The enrichment factor (EF), geo-accumulation index (I-geo), and contamination factor (C-i (f)) were finally evaluated for their ability to determine anthropogenic contamination: Results indicate that an in-depth knowledge of the bed rock geochemistry and the geological background content is essential to distinguish between the natural variability of soils and any anthropogenic contribution of heavy metals. Although both EF and C-i (f) show a similar ability to detect soil contamination, the latter is proposed as a more appropriate and sensitive marker given its ability for finding episodically elevated contamination levels.

The biotites of the crystalline massif of Catalonia (Spain) are weathered into a complex assemblage of clay secondary minerals. This is mainly formed by hydrobiotites (Iv) with very different compositions. The K2O of these phyllites changes from 7.2 to 2.8%. After this stage, the evolution is characterised by the genesis of protochlorites (Sm-C), then chlorites. Illites are less abundant in the studied profi les; while kaolinites are uncommon. The diversity of secondary minerals can be observed on a very small scale, often a centimetre and sometimes in one crystal of biotite only. A hydrobiotite - mineral close to chlorite- chlorite continuum occurs especially in the retromorphosis zone, not subject to weathering and these minerals are inherited in the saprolite formations. However, some chlorites can be the consequence of superfi cial weathering.

In this study we explore the processes of sorption and mobility in experimental soil columns in order to assess the response of natural soils to a hypothetical increase of pollution. The soils were sampled in a forest catchment situated in the Bertiz Natural Park at the western end of the Pyrenees. 21 columns, reproducing 21 soil profiles, were treated with a solution of heavy metals four times more concentrated than under actual conditions of deposition. An undisturbed soil column was tested simultaneously. The competition between cations and the content of clay and oxi-hydroxide compounds in the soils were the main factors determining the mobility of metals along with the influence of temperature. Calculated distribution coefficients show retention of Cr3+ Cu2+, and As5+, and in a lesser extent of Pb2+ and leaching of Mn2+, Zn2+, Cd2+ and Ni2+. Consequently, Mn2+ and Zn2+ have a greater tendency to contribute to groundwater pollution, whereas Cr3+ and Cu2+ are more likely to remain on soil surface. In undisturbed soil column, Ni2+ and Zn2+ were preferably sorbed onto dissolved organic matter (DOC), and the sorption of Mn2+ Cu2+ and Zn2+ was controlled by the ambient temperature. The simulation shows the presence of weakly sorbed metals and of others clearly desorbed (Ni2+, Cd2+ and Pb2+), which suggests that in the near future they will reach groundwater becoming a risk for its quality and for the biota. This kind of experiments in disturbed soils did not prove to be successful, hence their analysis in undisturbed soils is suggested.

This work presents a soil developed in Mediterranean climate which is evident the mesofauna activity (vermic characteristics) on the soil morphology. Its physical, chemical and mineralogical characteristics are compared with other soils in the same area but they do not have so clear signs of zoopedoturbación. The comparative analysis of these soils concludes that wildlife action is not only important from a morphological point of view, but it also influences the development of the profile now that it slows down the processes of differentiation and formation of mollic and argilic horizons, typical of the other soils in the same area. Due to the importance of the vermic characteristics on soil development, and after to do a comparative systematic between the soils in Soil Taxonomy and WRB we conclude that it would be interesting to include the vermic characteristics in the Xereps and the Cambisols respectively.