Chemical mineralogical characterisation of clay sediments around ferrara (italy) a tool for an environme
Chemical–mineralogical characterisation of clay sediments around Ferrara (Italy): a tool for an environmental analysis Gianluca Bianchini a, * , Rocco Laviano b , Stefano Lovo a , Carmela Vaccaro a a Dipartimento di Scienze della Terra, Universita ` di Ferrara, corso Ercole I D’Este 32, 44100 Ferrara, Italy b Dipartimento Geomineralogico, Universita ` degli Studi di Bari, via E. Orabona 4, 70125 Bari, Italy Received 27 October 2000; received in revised form 18 June 2001; accepted 19 July 2001 Abstract The content of heavy metals in water and soil is a key parameter for evaluating the geochemical vulnerability of an ecosystem. These elements display a limited solubility and are easily trapped and adsorbed by phyllosilicate minerals; they are thus preferentially partitioned in the fine fraction of sediments. In this light, an analysis of recent river sediments gives information on possible water pollution, and more in general on the related ecosystem. We therefore investigated the chemical–mineralogical features of clay sediments outcropping around the town of Ferrara, paying particular attention to their fine fraction (grain size < 2 Am). X-ray fluorescence (XRF) analyses indicate that the abundance of transition trace elements, such as Cr and Ni, is positively correlated with MgO wt.%, and discriminates two well-delineated populations of samples, respectively characterised by high (Cr > 180 ppm; Ni>100 ppm) and low (Cr < 180 ppm; Ni < 100 ppm) contents of these elements. The mineralogical composition of the fine fraction ( < 2 Am) was investigated through X-ray powder diffraction (XRPD) integrated with differential thermal (DTA) and thermogravimetric analyses (DTG), showing that: low-Cr samples are characterised by a higher proportion of clay minerals in which smectite + mixed layers are more abundant than chlorite (Sm + ML/Chl>1); on the other hand, the high-Cr samples have a coarser grain size, and a lower abundance of clay minerals in which chlorite (Mg-rich chlorite in this group of samples) predominates over smectite + mixed layers (Sm + ML/ Chl < 1). These two distinct groups of samples are ascribed to different sources: high-Cr lithologies are related to the sedimentary contribution of the Po river, whereas low-Cr sediments plausibly derive from small rivers of Apennine origin (e.g. the Reno river). Within the high-Cr group, concentrations of Ni and Cr tend to be higher than those indicated by the current environmental Italian legislation. However, in the study –case presented here, the detected high heavy-metal concentrations are not related to urban–industrial–agricultural activities, but instead appear to be typical of the original lithologies. An integration of similar scientific contributions would be useful to set up a geochemical–mineralogical database as a first step toward the preparation of more complete thematic maps. These would provide information relative to the behaviour (e.g. distribution and abundance) of chemical elements within the different geochemical spheres, and would be 0169-1317/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0169-1317(01)00086-2 * Corresponding author. E-mail address: gbianch@libero.it (G. Bianchini). www.elsevier.com/locate/clay Applied Clay Science 21 (2002) 165 – 176 useful for recognising and interpreting possible geochemical anomalies induced by pollution processes. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Clay sediments; Environment; Geochemical monitoring 1. Introduction The Po river alluvial plain in the province of Ferrara (Northern Italy) constitutes the terminal part of the most important drainage basin of the Italian peninsula, and is a delicate ecosystem. The Po river flows through highly urbanised and industrialised areas, and consequently its superf icial waters, associ- ated ground waters, and deposited sediments have to be carefully monitored for pollution. To recognise and interpret possible anthropogenic geochemical anomalies within the soils and sediments outcropping in the area, it is necessary to assess the ‘‘intrinsic baseline’’ (for each monitored parameter) typical of the natural system and related to the chemical characters of the original lithologies (Marini Fig. 1. Simplified map of the area (province of Ferrara) reporting the sampling locations, the estimated ages of sedimentation, and the chemical –mineralogical affinity of the studied fine sediments. The characters of the mentioned sample groups (i.e. low Cr, high Cr) and the related origin are discussed in the text. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176166 and Ottonello, 1999). The definition of the ‘‘blank’’ for each chemical parameter is critical for discrim- ination between ‘‘natural’’ anomalies typical of the deposited sediments and the chemical fingerprint induced by subsequent human activity. In particular, this study is focused on the chemical–mineralogical characterisation of sediments outcropping around the town of Ferrara, paying particula r attention to the fine fraction (grain size < 2 Am) within which some key chemical species (e.g. heavy metals) tend to concen- trate, frequently exceeding the permitted limits set by the Italian nati onal environmental regulations. The study approach outlined here is a suitable method for evaluating the environmental conditions and investigating contamination and pollution in an area containing sensitive natural systems, including impor- tant parks and water resources (e.g. the Ostellato natural oasis and the Po delta nature park). 2. Location of the sampling areas—preliminary description of the investigated sediments Fine sediment outcrops were selected for the sam- pling areas (Fig. 1) using a lithological map of Ferrara (edited by the provincial administration of Ferrara). Samples were collected using a manual drill at depths of 70–100 cm, to exclude levels containing high amount of vegetable matter and/or disturbed by agri- cultural activity. From available geomo rphologica l studies, it is possible to associate these sediments with a fluvial– lagoon–lacustrine environment (Bondesan, 1990; Ste- fani et al., 1999). These geomorphological investiga- tions further define the sedimentary history of the area, enabling the samples to be assigned to three different chronological intervals (Bondesan, personal communication): 1. sediments over 2000 years old (samples 1, 2, 3, 4, 6, 15, and 23); 2. sediments rangingbetween 2000and 1000years old (samples 5, 13, 14, 16, 17, 18, 19, and 24); 3. sediments less than 1000 years old (samples 7, 8, 9, 10, 11, 12, 20, 21, and 22). Granulometric analysis was performed on a set of these samples (covering the three mentioned sedimen- tation periods and representative of the various sectors of the area) in a two-stage process. Firstly, the samples were wet sieved to separate the coarser particles (>63 Am), then decantation experiments were carried out (gravity settling in deionized water) to characterize the finer fraction. The analysis indicated that the clay fraction ( < 2 Am) ranges between 44 and 74 wt.%, the silt fraction (2–63 Am) between 25 and 49 wt.%, and that the sand fraction (>63 Am) is subordinate ( < 9 wt.%) (Table 1, Fig. 2). Fig. 2. Grain size distribution of the studied sediments. Symbols: n = low-Cr sediments; 5 = high-Cr sediments. Table 1 Grain size distribution of the studied sediments (wt.%) Samples Sand (>63 Am) Silt (2 – 63 Am) Clay (<2 Am) Low Cr 3 2 31 67 6 2 48 50 7 2 36 62 10 2 31 67 11 1 25 74 14 3 33 64 x 234 64 High Cr 2 9 47 44 15 7 49 44 16 2 45 53 17 7 42 51 19 3 40 57 20 5 44 51 x 545 50 x = Average value. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 167 CO 2 content analyses were carried out (by simple volumetric technique; Jackson, 1958) to constrain the amount of carbonates present. The maximum values were up to 17.8 wt.% in sample 16 (see Table 2), which indi cates that some samples could be better classified as marly–clay; in this sample, petrographic microscope analysis indicates that the recorded high amount of calcite is present as micrite, whereas detrital calcite (coarse grains/rock fragments) was not detected. 3. Chemical – mineralogical data set Chemical compositions of the major and trace ele- ments (reported in Table 3) of the sampled sediments (tout-venant) were determined by X-ray fluorescence (XRF) using a Philips PW 1400 spect rometer, follow- ing the methodology of Franzini et al. (1975) and Leoni and Saitta (1975). Major element s presen t the following composi- tional ranges: SiO 2 = 47.0–54.6%, TiO 2 = 0.5–0.8%, Al 2 O 3 = 15.1 –21.0%, Fe 2 O 3 tot = 5.1–8.2%, MnO V 0.1%, MgO = 2.5–4.7%, CaO = 1.3–11.1%, Na 2 O = 0.3–0.8%, K 2 O = 2.2–3.6%, P 2 O 5 V 0.3%, LOI = 9.0 –17.9. Further examination of these data (Fig. 3) highlights: (1) a lack of correlation between the SiO 2 % and oxides of the other major elements, indicating that the SiO 2 % content is mainly related to the abundance of quartz; (2) that K 2 O% and Rb ppm (usually characterised by similar geochemical behaviour) are positively correlated with Al 2 O 3 % (correlation coefficient r 2 >0.75), as usually observed in illite-rich fine sedi- ments; (3) a negat ive correlation between CaO% and Al 2 O 3 %(r 2 = 0.60), indicating that CaO is mainly hosted within carbonates, thus precluding a significant presence of CaO-b earing silicates; (4) a coherent positive correlation between the CaO wt.% and CO 2 (r 2 = 0.95) content; (5) positive correlations between MgO% and tran- sition trace elements, such as Cr (r 2 = 0.58) and Ni (r 2 = 0.83); these elements are usually associated in sediments containing chlorite and serpentine, in turn derived from weathering of mother rocks rich in olivine, pyroxenes, and spinel; (6) the existence of two well-delineated popula- tions of samples discriminated by Cr and Ni (Stu- dent’s t-test: t >10.84, P > 99.99% for Cr; t > 9.24, P > 99.99% for Ni): these are characterised by high (Cr > 180 ppm; Ni > 100 ppm) and low (Cr < 180 ppm; Ni < 100 ppm) concentrations of these elements, here- after named as high-Cr and low-Cr groups. To visualise the trace element distribution, the data presented here have been normalised to the composi- tion of fine sediments from the Po river (sampled and analysed by ourselves). In the normalised multi-ele- ment plot of Fig. 4, most elements show only a limited scattering within the two sample groups. On the other hand, the concentration of Ba and Sr (possibly hosted in carbonates and feldspar) varies widely in both groups. The mineralogical composition of these lithotypes was carried ou t through X-ray powder diffraction (XRPD; Philips PW1010/80 diffractometer with graphite-filtered CuKa radiation). Particular attention was devoted to investigating the fine fraction of these sediments which, due to the high surface area and the particular nature of the related minerals (mainly clay minerals), tend to trap and concentrate possible pol- lution substances. In this light, for a better character- isation of the constituent clay minerals, X-ray dif- fractometric analysis was carried out on the < 2-Am fraction (in which the different clay minerals are more clearly recognised) of each selected sample; in partic- ular, X-ray investigation was carried out on randomly oriented samples, and also on glycolated and heat- Table 2 CO 2 and CaCO 3 content of the studied sediments Samples CO 2 CaCO 3 Low Cr 3 5.13 11.67 6 5.97 13.58 7 6.21 14.11 10 5.08 11.55 11 4.73 10.76 14 6.54 14.87 x 5.61 12.76 High Cr 2 4.67 10.62 15 5.83 13.26 16 7.82 17.78 17 3.68 8.37 19 1.36 3.09 20 1.57 3.57 x 4.15 9.45 x = Average value. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176168 Table 3 Major (wt.%) and trace element (ppm) analyses of the studied sediments Elements Low-Cr samples High-Cr samples SL3 SL6 SL7 SL8 SL9 SL10 SL11 SL12 SL14 x SL 1 SL 2 SL 4 SL 5 SL 13 SL 15 SL 16 SL 17 SL 18 SL 19 SL 20 SL 21 SL 22 SL 23 SL 24 x SiO 2 50.38 49.09 49.68 49.63 49.00 47.88 47.42 49.86 47.20 48.90 47.02 54.58 53.49 51.54 45.48 49.02 45.57 51.11 51.27 52.59 42.49 50.55 48.88 43.05 53.02 49.31 TiO 2 0.71 0.68 0.68 0.75 0.75 0.72 0.72 0.73 0.68 0.71 0.66 0.62 0.72 0.70 0.70 0.66 0.67 0.70 0.74 0.70 0.53 0.65 0.67 0.56 0.68 0.66 Al 2 O 3 16.66 15.83 15.15 19.05 18.46 17.63 18.56 17.68 15.90 17.21 16.42 15.28 20.96 20.53 18.51 15.28 14.94 17.07 17.94 19.30 16.14 14.97 17.10 15.07 16.24 17.05 Fe 2 O 3 5.81 5.88 5.81 6.95 7.09 6.49 6.78 6.27 6.76 6.43 7.61 5.45 6.06 7.46 8.23 5.93 6.09 6.14 6.51 6.81 5.55 5.68 6.53 5.15 5.88 6.34 MnO 0.09 0.10 0.12 0.10 0.12 0.10 0.09 0.09 0.14 0.10 0.08 0.11 0.04 0.07 0.05 0.12 0.12 0.07 0.07 0.05 0.06 0.11 0.08 0.09 0.09 0.08 MgO 2.81 2.76 2.59 3.15 3.03 3.01 3.17 3.27 2.99 2.98 4.32 4.45 3.20 3.25 3.35 4.55 4.32 4.69 4.23 4.21 3.17 4.32 4.20 3.66 4.43 4.02 CaO 8.64 9.72 8.91 6.47 7.65 7.93 7.60 6.98 9.72 8.18 8.00 6.95 1.32 2.51 8.23 9.31 11.04 6.37 4.82 2.68 2.58 10.57 7.05 11.03 6.17 6.58 Na 2 O 0.59 0.51 0.56 0.35 0.36 0.39 0.32 0.39 0.48 0.44 0.44 0.76 0.71 0.55 0.34 0.63 0.53 0.67 0.48 0.51 0.46 0.61 0.48 0.73 0.67 0.57 K 2 O 2.61 2.51 2.48 3.38 3.37 2.99 3.21 2.97 2.58 2.90 2.68 2.45 3.38 3.58 2.80 2.30 2.22 2.51 2.67 3.05 2.30 2.26 2.61 2.43 2.45 2.65 P 2 O 5 0.28 0.32 0.32 0.18 0.24 0.24 0.21 0.21 0.28 0.25 0.32 0.27 0.00 0.03 0.21 0.30 0.33 0.17 0.15 0.06 0.15 0.31 0.20 0.34 0.22 0.20 LOI 11.42 12.6 13.69 9.98 9.95 12.62 11.93 11.54 13.27 11.89 12.46 9.08 10.14 9.78 12.1 11.89 14.16 10.5 11.12 10.04 26.58 9.97 12.2 17.89 10.15 12.54 Pb a 24 14 18 23 23 20 18 20 19 20 28 29 37 36 30 26 20 28 25 28 23 25 24 40 22 28 Zn a 104 106 111 122 124 120 123 119 106 115 117 101 107 136 125 96 102 106 124 125 103 91 121 94 104 110 Ni 86 80 69 82 82 80 84 94 89 83 152 134 112 106 138 146 145 155 162 156 123 132 151 119 138 138 Co 19 21 16 20 20 18 19 19 18 19 21 19 17 22 19 20 21 29 32 28 20 19 21 15 22 22 Cr 120 108 101 136 143 134 119 125 122 123 237 214 268 222 244 224 210 288 281 284 221 221 258 195 228 240 V 133 121 117 163 155 148 161 151 144 144 124 111 174 177 162 112 124 146 158 174 131 108 138 116 124 139 Th 16 11 11 12 14 14 19 16 18 14 15 10 15 13 15 13 15 12 14 13 11 10 11 10 9 12 Nb 18 14 14 14 16 16 20 16 15 16 11 13 19 16 16 11 15 17 18 17 12 13 16 10 15 15 Zr 145 147 137 125 129 126 123 132 126 132 115 153 118 132 115 147 131 142 132 125 103 135 125 97 133 127 Rb 147 141 124 174 176 163 172 152 134 154 152 118 198 195 182 122 128 150 164 184 139 122 154 128 128 151 Sr 265 279 258 254 268 282 284 252 272 268 424 221 160 191 223 257 301 243 219 171 151 279 229 579 215 257 Ba 860 440 283 310 336 316 890 818 583 537 1035 888 835 496 422 495 1017 617 279 250 430 411 435 368 418 560 Y 22222320191920232021 172416172325 22242316182419162421 Ce 105 50 83 82 65 67 97 118 111 87 63 41 81 62 78 29 75 77 81 83 64 48 78 63 52 65 x =Average value. a Semiquantitative analyses. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 169 treated oriented samples (Moore and Reynolds, 1997). These data were further supplemented with differential thermal (DTA) and thermogravimetric (DTG) analyses (Fig. 5), kindly performed by M.F. Brigatti (University0 of Modena; see Brigatti et al., 1995, 1996 for metho- dological details). Results indicate that the fine frac- tion is made up of various proportions of illite (Ill), chlorite (Chl), kaolinite (K), smectite (Sm), interstra- tified mineral phases (ML: chlorite–smectite and subordinate kaolinite–smectite), and low percentages of serpentine, quartz, and carbonate. DTA–DTG measurements also indicate the presence of organic matter. A semiquantitative evaluation of the mineralogical composition (within the < 2-Am fraction; see Table 4) was obtained by applying the analytical methods of Schultz (1964) and Shaw et al. (1971), modified by Laviano (1987). Fig. 3. Variation diagrams reporting XRF data carried out on the studied sediments: Ni (ppm) and Cr (ppm) vs. MgO (wt.%); CaO (wt.%), Fe 2 O 3 (wt.%), K 2 O (wt.%), and Rb (ppm) vs. Al 2 O 3 . Symbols: n = low-Cr sediments; 5 = high-Cr sediments. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176170 Illite, is 2M polytype with Al 3+ as the mai n octahedral cation, K + as the chief interlayer cation, and the degree of paragonitization varying from 5% to 25% (Yoder and Eugster, 1955; Bradley and Grim, 1961; Dunoyer De Segonzac, 1970; Srodon and Eberl, 1984). The degree of crystallinity (E) of illite varies from 150 to 200 A ˚ (Weber et al., 1976; Wang and Zhou, 2000). Smectite (montmorillonite type) is more dominant in low-Cr samples, with more Ca 2+ than Na + exist- ing as interlayer cations and a medium degree of crystallinity ( v /p = 0.6; Biscaye, 1965). In contrast, Fig. 4. Trace element distribution of the studied sediments. Data are normalised to the composition of present Po river fine sediments (sampled and analysed by ourselves) around Ferrara (concentration expressed as ppm): Pb = 24, Zn = 91, Ni = 130, Co = 19, Cr = 221, V = 103, Th = 10, Nb =11, Zr = 88, Sr = 186, Ba = 306, Y = 15, and Ce = 52. Fig. 5. Representative TG, DTG, and DTA curves. Similar analyses are available also for samples 10, 11, 14, and 19. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 171 high-Cr samples exhibit a very low degree of crystal- linity (v /p = 0.3). Mg–Fe-bearing chlorite, with a high degree of crystallinity, is always present; however, high-Cr samples are comparatively richer in chlorite that appear to be distinctively richer in Mg 2+ . It is not possible to distinguish the X-ray double reflections in kaolinite; the crystallinity index reflects this (Brindley, 1961; Hincley, 1963), and as a result, a low–medium degree of crystallinity is found in both sample groups. Interstratified minerals are characterised by 60 – 70% of smectite layers within low-Cr samples, and by 30–40% of smectite layers within high-Cr samples. As mentioned, subordinate K/Sm mixed layers are also present. Summarising, the low-Cr samples are characterised by a comparatively fine grain size, together with a high proportion of clay minerals in which smecti- te + interstratified minerals are more represented than chlorite (Sm + ML/Chl>1). On the other hand, the high-Cr samples have a coarser grain size, and a lower abundance of clay minerals in which chlorite (Mg-rich chlorite in this group of samples) predominates over smectite + mixed layers (Sm + ML/Chl < 1). Examination of the >63-Am fraction, using a trans- mitted light microscope and XRPD analysis, revealed that these coarse grains are mainly characterised by quartz, minor amounts of carbonates and feldspars, and lithic fragm ents containing amphiboles – pyrox- enes, muscovite, biotite, chlorite, and serpentine (the last-named mineral is ubiquitous only in high-Cr sediments), with magnetite as a main Fe oxide in both groups of samples. 4. Discussion 4.1. Possible origin and provenance of the studied sediments To address the implications of the analyses under- taken, and to interpret the significance of the two men- tioned sample groups (high Cr, low Cr), the presented data were compared with the composition of sediments related to rivers of Apennine provenance such as the Reno and Panaro (Dondi et al., 1993; Dinelli and Lucchini, 1998), and also with recent sediment s of the Po river (Dinelli et al., 1999 and authors’ data re- ported in Fig. 4). It can be seen that the low-Cr samples show chemical analogies with sediments of rivers sourced from the Bolognese Apennine (in which femic and ultrafemic rocks do not outcrop), whereas the high-Cr samples show a chemical affinity with the Po sedi- ments. Within the latter samples, the high Ni, Cr (and V) concentration is related to the high abundance of chlorite ( F serpentine), presumably formed by weath- ering processes of ultrafemic–femic mineral paragen- eses that are widespread in the western sector of the Po drainage basin where igneous and metamorphic rocks (and also ophiolite complexes) are present. Coherently, Tomadin and Varani (1998) indicate the predominance of smectite (typical of the low-Cr samples) as the mineral fingerprint of fine sediments of Apennine origin. In this light, the tendency toward finer grain size (and higher homogeneity of grain size) envisaged in low-Cr samples can be interpreted considering that they mainly represent reworked sediments, mainly derived from erosion–weathering of sedimentary rocks outcropping in the Bolognese Apennine. It can be observed (in the map of Fig. 1) that the samples included in the low-Cr group preferentially outcrop in the southern/southwestern sector of the investigated area, and are more widespread within Table 4 Mineralogical composition (wt.%) of clay fraction ( < 2 Am) Samples Cm Sm + ML Ill K Chl Qtz Fld Cal Low Cr 3 92 31 28 16 17 5 3 tr 69230291716422 79128341118423 10 90 32 29 18 15 3 2 1 11 95 33 30 16 16 3 2 tr 14 90 30 26 18 16 4 2 4 x 92 31 29 16 16 4 2 2 High Cr 2 81 16 26 11 28 9 4 6 15 83 15 26 13 29 5 4 8 16 82 17 27 12 26 5 3 10 17 87 16 31 13 27 4 3 6 19 87 18 28 11 30 7 4 2 20 91 24 27 14 26 5 4 tr x 85 18 28 12 28 6 4 5 Cm = clay minerals; Sm = smectite; ML= mixed layers; Ill =illite; K = kaolinite; Chl = chlorite; Qtz = quartz; Fld = feldspars; Cal = cal- cite; tr = trace; x = average value. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176172 the younger sediments. This fact could be explained by considering the significant man-made hydrogeo- logical modifications that occurred in the XIV–XVI centuries throughout the Ferrarese territory (Bonde- san, 1990). During this period, important hydrogeo- logical developments were carried out to divert certain apenninic torrent – river s (e.g. Ren o) into the southern branches of the Po river (flowing south of Ferrara at that time). These modifications induced the progres- sive decadence of these southern Po branches, due to the deposition of considerable amount of sediments carried by these torrents. The alteration of the hydro- geological system can explain the widespread pres- ence of Reno-like compositions (low-Cr) within the most recent terrains. 4.2. Environmental analysis and implications Trace amounts of heavy metals are ubiquitous within rocks, soils, surface, and ground water. Natural background concentrations vary from place to place, owing to different bedrock composition and hetero- geneous distribution among the various geochemical environments. Organisms tend to concentrate these elements, and consequently their presence in waters, even at low concentrations, is considered dangerous due to their toxic effects (Hg in aquatic ecosystems is a notorious example; Jackson, 1998 and references there in). It follows that, as part of an environmental assessment, the content of heavy metals in waters and soils is a key parameter necessary for evaluating the geochem- ical vulnerability of an ecosystem. Heavy elements usually exhibit a limited solubility, and are easily trapped and adsorbed by phyllosilicate minerals; as a consequ ence, they may be preferentially partitioned within the fine fraction of sediments (Baldi et al., 1997). This fact is related to the typical layer– lattice alluminosilicatic structure of clay minerals, cha- racterised by well-developed basal cleavage (001 pla- nar faces) with permanent negatively charged sites. Such structures induce electrostatic binding of cations within the 001 faces (Jackson, 1998 and references therein). The fact that heavy elements a re preferentially retained by the fine fraction of river sediments can be used as a tool to detect pollution of an ecosystem. However, to understand the possible presence of a pollution process induced by human activity, it is necessary to define the baseline (or ‘‘blank’’) of each monitored key parameter (i.e. the typical concentra- tions in an unpolluted environment). Within the con- sidered area, this information can be obtained through a geochemical characterisation of the sediments that have not been affected by pollution and anthropogenic activities. In this study, the baseline approach enabled us to highlight the concentration of the monitored parame- ters in the natural system, as the studied terrains sedimentated at times when the envir onment was still unaffected by anthropic activity. Our data also indi- cate the geochemical evolution of the Po basin in the last 3000 years. The concentrations of transition elements recorded in the sediments sampled in the Ferrara surroundings were compared with the maximum concentrations admissible in terr ains used for agricultural (Italian Legislative decree 27/01/1992, no. 99) and residential (Italian Legislative decree 25/10/1999, no. 471) pur- poses. Within the high-Cr group of samples, the concen- trations of Ni, Cr, V, and Co tend to b e higher than those indicated by the current environmental legisla- tion. However, in the study–case presented here, the high concentration s detected are n ot associated to urban – industrial–agricultural activities, but instead appear to be typical of the original lithologies (Fig. 6). This has been further verified by taking into account an extensive data set (authors’ data: ca. 100 samples) of bricks from precisely dated historic build- ings of Ferrara . In fact the composition of these bricks show remarkable analogies with the clay composi- tions presented in this study. Moreover, the chemical and mineralogical data presented here provide an initial i nsight into the elemental partition between competing clay minerals. Different mecha nisms for trapping solution-electro- lytes by the various clay minerals have been docu- mented, and many authors also underlined existing relationships between clay mineralogy and concentra- tions of metallic elements (Brigatti et al., 1995, 1996; Pitsch et al., 1992; Helios-Rybicka et al., 1995). The implications become apparent when one con- siders that clay (sl) is often used as a barrier to isolate waste disposal sites from the surrounding environ- ment. These studies could be applied to defining and G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 173 characterising the most suitable clay materials to be used as liners and capping layers in landfills, as well as to treat leachates. Baldi et al. (1997) investigated the interaction between solutions containing metallic ions and natural clay sediments, thus individuating the key role of smectite in buffering the abundance of heavy metals. Pusch (1998) confi rmed the important role of smectite for landfill-sealing purposes because of its high exchange capacity. Taking into account ion-exchange values reported in the literature for the various clay minerals (CEC values expressed as meq/100 g at pH 7; Faure, 1998) and the modal proportions reported in Table 4 (refer- Fig. 6. Boxplots reporting the compositional distribution of Cr and Ni in the studied samples, in present-day sediments from the Po river and rivers sourced within the Bolognese Apennine, and in the bricks of the historic buildings of Ferrara (plausibly made with similar fine sediments; authors’ data). The limit concentrations admissible in terrains (Italian Legislative Decree 25/10/1999, no. 471) have been also reported for comparison. G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176174 [...]... pp 93 – 206 Laviano, R., 1987 Analisi mineralogica quantitativa di argille mediante diffrattometria di raggi X In: ENEA (Ed.), Procedure di analisi di materiali argillosi Collana di studi ambientali, Santa Teresa, Lerici (Sp), pp 215 – 234 Leoni, L., Saitta, M., 1975 X-ray fluorescence analysis of 29 trace elements in rocks and mineral standards Rend Soc Ital Mineral Petrol 32, 497 – 510 Marini, L.,... 1984 Illite In: Bailey, S.V (Ed.), Micas Review in Mineralogy 13, Mineralogical Society of America, Washington, DC, pp 495 – 544 Stefani, M., Asioli, A. , Bondesan, M., Cattani, L., Correggiari, A. , Roveri, M., Trincardi, F., 1999 Stratigrafia ed evoluzione ambientale olocenica della pianura costiera ferrarese e dell’antistante mare adriatico Conferenza Le pianure: Conoscenza e salvaguardia; il ruolo delle... which clay and silt fractions prevail, with a subordinate sand fraction Chemical analyses of these samples have been compared with recent sediments from the Apennine torrents and Po river, to understand their possible provenance The same analyses have also been compared with the chemical composition of bricks of historic buildings of Ferrara (XII – XVI centuries), made from similar raw materials in... ‘‘crystallinity’’ values among the Kaolin deposits of the Coastal Plain of Georgia and South Carolina Clay Miner 11, 229 – 235 Jackson, M.L., 1958 Soil Chemical Analysis Prentice-Hall, p 498 Jackson, T .A. , 1998 The biogeochemical and ecological significance of interactions between colloidal minerals and trace elements In: Parker, A. , Rae, J.E (Eds.), Environmental Interactions of Clays Springer-Verlag, Berlin,... Terra 39, 95 – 106 Biscaye, P.E., 1965 Mineralogy and sedimentation of recent deepsea clay in the Atlantic Ocean and adjacent seas and oceans Geol Soc Am Bull 76, 803 – 832 Bondesan, M., 1990 Evoluzione geomorfologica ed idrografica della pianura ferrarese In: Corbo, G (Ed.), Terre ed acqua-Le bonifiche ferraresi nel delta del Po Ferrara, pp 13 – 20 Bradley, W.F., Grim, R.E., 1961 Mica clay minerals... the human impact on the environment was negligible These comparisons suggest that the concentration of heavy metals (such as Cr, Ni, V, and Co) is naturally high, and cannot be a direct consequence of anthropogenic activity This data set provides therefore a contribution to interpreting the vulnerability of the Ferrara area, which appears to be naturally characterised by high concentrations of metallic... della terra, Ferrara 2 – 4 (abstract book) Tomadin, L., Varani, L., 1998 Provenance and downstream mineralogical evolution of the muds transported by Po River (Northern Italy) Mineral Petrogr Acta 41, 205 – 224 Vetuschi Zuccolini, M., Ottonello, G., 1999 Towards the national geological database: logical framework and network interface Plinius 22, 374 – 375 (Italian supplement of Eur J Mineral.) Wang,... Petrogr Acta XLI, 145 – 162 Dinelli, E., Amorosi, A. , Centineo, M.C., Lucchini, F., 1999 Geochimica dei sedimenti sepolti della Pianura Padana—uno strumento per valutare la qualita’ dell’ambiente Conferenza Le pianure: Conoscenza e salvaguardia; il ruolo delle scienze della terra, Ferrara pp 131 – 133 (abstract book) Dondi, M., Ercolani, G., Guarini, G., 1993 Caratteri geochimici, mineralogici e granulometrici... contain minor amounts of clay minerals) Summarising, low-Cr lithologies characterised by finer grain size, higher abundance of smectite, and low content of transition elements would be the most suitable for forming impermeable bottom layers within landfills of this area 5 Conclusions In the study area, the lithological outcrops consist of silico – clastic sediments (containing a minor amount of carbonate... peliti alluvionali quaternarie dell’Emilia-Romagna (Italia Settentrionale) Mineral Petrogr Acta XXXVI, 129 – 142 176 G Bianchini et al / Applied Clay Science 21 (2002) 165–176 Dunoyer De Segonzac, G., 1970 The transformation of clay minerals during diagenesis and low-grade metamorphism: a review Sedimentology 15, 281 – 346 Faure, G, 1998 Principles and Application of Geochemistry Prentice Hall, London, . Chemical mineralogical characterisation of clay sediments around Ferrara (Italy): a tool for an environmental analysis Gianluca Bianchini a, * ,. Mineralogy and sedimentation of recent deep- sea clay in the Atlantic Ocean and adjacent seas and oceans. Geol. Soc. Am. Bull. 76, 803 – 832. Bond esan,