CHESWORTH, W.*, GARCÍA-RODEJA E.**, MARTÍNEZ CORTIZAS A.**, MACIAS F.**

Transcription

1 Scientific registration no : 2119 Symposium no : 22 Presentation : poster Trace elements in podzols from Northern Spain léments traces dans les podzols du Nord de l spagne HSWORTH, W*, GRÍ-RODJ **, MRTÍNZ ORTIZS **, MIS F** * Land Resource Science Department, University of Guelph, Guelph, Ontario anada ** Departamento de dafología y Química grícola, Facultad de Biología, Universidad de Santiago Santiago de ompostela spaña Introduction tmospheric deposition of heavy metals and other trace elements in soils as well as their circulation to superficial waters and nutritional pathways is of great interest because of potential effects on aquatic and terrestrial ecosystems and public health The knowledge of the fate of these elements in the soil environment is a key factor in determining possible risks Soils are a geochemical sink of many trace elements, but also act as natural buffers controlling the transport of chemical elements to the air, the surface waters and the biota (Kabata-Pendias & Pendias, 1992) The residence times of contaminants is longer in soils than in other compartments of the biosphere, and for heavy metals appears to be practically permanent mong the soil properties governing the fate of trace elements in soils, ph, redox potential and kind of organic matter, appear as the most important parameters (lloway, 1990, Kabata-Pendias & Pendias, 1992) high rate of trace element mobility in soils affects the increase of bioavalabillity and leaching down the soil to the surface waters, increasing the environmental risk Podzols, soils characterized by the leaching of organic matter, Fe and l from eluvial horizons and its precipitation in the illuvial spodic B horizons, combine two different environments In the surface horizons, the high mobility is caused by the very low ph and the abundance of soluble organic matter, while in the subsurface horizons precipitation and adsorption processes prevail These characteristics justify the special interest of these soils in the study of the mobility of trace elements in the pedosphere This paper presents the results of the study of content and vertical distribution of metals and trace elements in some well differentiated podzols from Northern Spain The aim is to contribute to the knowledge of their mobility in podzolic environments where the eluviation/illuviation processes play a predominant role The results obtained for trace elements are compared to the distribution of major elements Material and Methods The studied soils developed on quartz rich sediments, derived from quartzites, quartz rich sandstones or quartz dikes They are all podzols with eluvial horizon and spodic B horizon with and subhorizons The natural vegetation consists of heath, sometimes forested with pines or eucalyptus Mean anual precipitation ranges between 900 mm and 1

2 1300 mm and mean annual temperature varies from 115 to 135 Table I shows data on location, altitude and soil classification (FO-UNSO, 1989 y SSS, 1997) Table I Location and classification of the soils used in this study Soil ltitude Province FO (1989) Soil Taxonomy (1997) Tol P1 100 m sturias Gleyic podzol Typic endoaquod astañeras P2 150 m antabria Haplic podzol Typic haplorthod banillas P3 250 m sturias Haplic podzol Gleyic haplorthod cibro r1 450 m Galicia Haplic podzol Typic haplorthod Burela m Galicia Haplic podzol Ultic haplorthod Roupar PR 450 m Galicia Haplic podzol Typic haplorthod Major (Si, l, Fe, Mg, a, Na, K, Ti and Mn) and trace element (Rb, Ba, u, Sr, Zn, Y, La, e, Nd, s, V, Nb, Pb, Ti, Zr, r, o) contents were measured using X Ray Fluorescence analysis (XRF), on oven dried (40º), sieved (<2mm) soil samples (8 samples from horizons, 6 from horizons, 16 from B spodic horizons and 6 from horizons) These measurements were carried out at McMaster University (anada) Other parameters determined in order to characterize the soils were ph (in H 2 O and Kl 01M, using a 1: 25 w/v ratio), particle size distribution, total organic carbon content, effective cation exchange capacity (base cations extracted with NH 4 l plus l Kl extractable) Fe and l were extracted with acid ammonium oxalate (Blakemore et al, 1981), Na pyrophosphate (Bascomb, 1968) and citrate-dithionite (Holmgren, 1967) Results Soil properties summary of the soil properties is presented in Table II Soils are acid, with ph (H 2 O) about 45; and horizons are more acidic while ph is relatively higher in albic horizons poor in organic matter and in the hydromorphic horizons The horizons have organic matter contents comparable to those of the epipedons ffective exchange capacity (e) is low except for organic and clay rich spodic horizons luminium is the dominant cation in the exchange complex, specially in the latter horizons Table II Summary of some properties of the studied soils (texture: l, loamy; ls, loamy-sand; sl, sandy-loam; s, sandy; lcs, loamy-clay-sand Horizon ph H 2 O ph Kl Org % Texture lay % l, ls s, sl, ls lcs, ls ls, lcs / ls, lcs

3 cibro-r1 astañeras-p Burela / 2 / banillas-p Roupar-PR s1 s2 s3 2 Fe s1 s2 s3 2 Tol-P1 l Fe(d) Fe(p) l(o) l(p) / / s1 s1 s2 s2 s3 2 s ,5 1 1,5 2 Figure 1 Total Fe and l and extractable Fe and l in the six podzols analyzed [Fe(d): Fe extracted with dithionite; Fe(p) and l(p): Fe and l extracted with pyrophosphate; l(o): l extracted with oxalate) Figure 1 shows the vertical distribution of total Fe and l and the fractions extracted with selective disolution methods (dithionite, acid oxalate and pyrophosphate) haracteristic for podzols, maxima Fe contents are attained in the horizons (mean value of 374%), while l tend to appear in the horizons (mean value of 60%) 3

4 luvial horizons are impoverished in both elements Major elements (l, Fe, Ti and K) showed a homogeneous vertical pattern, with a maximum in the illuvial horizon and a minimum in the eluvial Manganese presented very low levels for all soils and horizons Total analyses data reflected a clear redistribution of the elements in the soil as well as the influence of the parent material, with a great abundance of quartz and a low proportion of Fe oxy-hydroxydes and mica and negligible proportions of feldspars Silica is the most abundant oxide (85-97% as SiO 2 ) with maximum values in the eluvial horizon, decreasing with depth due mainly to a relative enrichment in Fe and l in the illuvial horizon ( and ), where these elements had their maximum contents alcium levels are low (less than 01% in all horizons); Mg and Na showed fairly irregular distribution, with values lower to 1% MgO and 0,5% Na 2 O Potassium was always below 1% with maximum values in the subsuperficial horizons, reflecting the breakdown of micas in the eluvial horizons Heavy metals and trace elements Mean, standard deviations, maximum and minimum contents for heavy metals and trace elements (mg kg -1 ; Ti in percentage) are summarized in Table III Values are in the range reported for podzols developed on similar materials and for different areas of the world (lloway, 1992; Kabata-Pendias & Pendias, 1992) and comparable to those reported for fresh and weathered rocks of north-western Spain (Guitián Ojea, 1992) xcept for Nb, Zr and Ti, with little variation in the soil profile, the highest contents were always found in the spodic horizons and the lowest in the albic horizons The tendency to accumulate in the spodic horizon is evident for all soils and the following elements: Rb, Sr, Ba, e, s, V, r and o (some of them are depicted in Figure 2) Zinc and Pb presented low contents and variation with depth, but in two cases extremely high values in the horizon of two soils (67 and 83 mg kg -1 for Pb, 80 and 186 mg kg -1 for Zn, in astañeras- P2 and Tol-P1 respectively) may be interpreted as an indication of external sources for these elements via atmospheric pollution Similar results were obtained by Martínez ortizas et al (1997) in the study of the accumulation pattern in an ombrotrophic bog from the same area Yttrium, La, Nd, and Nb do not Table III Mean, standard deviations, maximum and minimum values for trace elements in podzols from Northern Spain lement Mean Std dev Max Min Rb u Sr Ba Zn Y La e Nd s V Nb Pb Ti Zr r o varied with depth or showed no defined pattern of distribution opper content was very low despite the soil and/or horizon considered 4

5 Rb cibro-r1 r astañeras-p2 Burela / s1 s2 s / s1 s2 s3 2 banillas-p3 Roupar-PR Pb V / / s1 s1 s2 s2 s3 s Figure 2 Vertical variation of the concentration of Rb, r, V and Pb in the six podzols analyzed (concentrations in mg kg -1 ) The distribution of some elements followed the typical pattern of l and Fe in podzols The highest correlation coefficients with total l were obtained for Rb (r= 096), Ba (092), e (090), r (090) and Sr (084), while the highest ones to Fe were for o (089), V (087), r (082) and s (079) In order to compare the relative mobility of the different elements in these podzols, ratios to Ti and Zr -usually taken as immobile in soil environments- were calculated The 5

6 results showed the same trends described above, though more homogeneous for metal/zr than metal/ti ratios This is consistent with the greater relative mobility of Ti in podzolic soils (orrens, 1978; Dumon and Vigneaux, 1979, Ure and Berrow, 1982) compared to Zr Rb F Pb F / / s1 s2 s3 2 s1 s2 s3 2 Figure 3 Two examples, rubidium and lead, of the vertical variation of the enrichment factors in the six podzols analyzed nrichment factors (F), obtained normalizing to the metal/zr ratio of the horizon, indicate that maximum enrichments in the spodic horizon were of 2-25 times for Zn, 2-3 for e, 4-5 for r, 3-7 for Sr, 4-9 for Ba, 5-9 for V, 5-10 for s and 4-12 for Rb (Figure 3) obalt seems to be dramatically enriched in the spodic horizons with Fs up to 30, but in most of the soils the enrichment factor was not calculated because concentration was below the detection limit in the horizons s already mentioned, Zn and Pb (Figure 3) showed high values only in two profiles (astañeras-p2 and Tol-P1) and in the upper horizons, with Fs values of 8 In the Tol-P1 profile not only the Pb presented high Fs but also most of the other elements, suggesting an intense pollution in that area Some elements showed a paired distribution in the soils, as for the following pairs: K- Rb (r=097), K-Ba (098), Ba-Sr (090), Ba-Rb (091), Ti-Nb (085), Ti-V (080), r-e (083) and r-rb (087) Less clear were the relations between V and s (079), o and r (077) and V (076), and Y and Nd (r=075) Most of the relations are a consequence of the similar geochemical behaviour of the paired elements onclusions The study of six podzols from Northern Spain shows that many trace elements that have high mobility in the eluvial horizon tend to be immobilized in the subsurface spodic horizons ( and ) This is the case for most of the elements we have measured (ie Rb, Sr, Ba, e, s, V, r and o); some appear to be essentially immobile, as Pb, Zn, 6

7 La, Nb, based on the metal/zr ratios; and others did not show a defined pattern of vertical distribution (Nd and Y) nrichment factors calculated by normalizing to the metal/zr ratios of the eluvial horizon, indicate that enrichments in the spodic horizon are in the order of 2-5 times for Zn, e, and r; 5 to 10 for Ba, Sr, Rb, s and V; and up to 30 times for o lements as Pb and Zn presented Fs of 8 only for two soils and in the upper horizons, suggesting a possible source via atmospheric pollution References lloway, BJ 1990 Heavy Metals in Soils John Wiley & Sons, Inc New York Bascomb, L 1968 J Soil Sci, 19: Blakemore, L, Searly, PL, Daly, BK 1981 Soil Boreu Laboratory Methods Methods for hemical nalysis of Soils New Zealand Soil Boreau, Scientific Report 10a (revised) orrens, W 1978 Titanium In KH Wedephol (ed) Handbook of Geochemistry Springer-Verlag, Berlin Voll II-2, Sec 22B-220 Dumon, J, Vigneaux, M 1979 Phys hem arth, 11: FO-Unesco 1989 Soil Map of the World, revised legend FO, Rome Guitián Ojea, F (coord) 1992 tlas Geoquímico de Galicia Xunta de Galicia, Santiago Holmgren, GG1967 Soil Sci Soc m J, 31: Kabata-Pendias,, Pendias, H 1992 Trace lements in Soils and Plants R Press Martínez ortizas,, Pontevedra, X, Nóvoa, J, García-Rodeja, 1997 Water ir and Soil Pollut, 100: Soil Survey Staff 1997 Keys to Soil Taxonomy Soil onservation Sevice, US Department of griculture Ure, M, Berrow, ML 1982 The elemental constituents of soils In nvironmetal hemistry Vol 2 P Royal Society od hemistry, London Key words : trace elements, podzols, Northern Spain Mots clés : éléments traces, podzols, Nord de l spagne 7