• Título:  MINERALOGÍA, GEOQUÍMICA E IMPLICACIONES AMBIENTALES DE LOS SUELOS Y SEDIMENTOS DEL PARAJE NATURAL ESTERO DOMINGO RUBIO Y SU ENTORNO (HUELVA)
• Autor:  BARBA BRIOSO, CINTA
• Universidad:  Universidad de Sevilla
• Departamento:  Cristalografía, mineralogía y química agrícola
• Fecha de Lectura:  28/06/2011
• Mención Europeo / Mención Internacional: concedido
• Programa de doctorado:  Ingeniería Ambiental
• Dirección: 
  • FERNÁNDEZ CALIANI, JUAN CARLOS (DIRECTOR)
  • MIRAS RUIZ, ADOLFO (TUTOR/PONENTE)
• Tribunal: 
  • GALAN HUERTOS, EMILIO (PRESIDENTE)
  • QUARANTA, GAETANA (SECRETARIO)
  • SILVA NUNES REIS ABREU, MARIA MANUELA (VOCAL)
  • Gonzalez Diez, Isabel (VOCAL)
  • CORNEJO SUERO, JUAN (VOCAL)
• Descriptores: 
  • GEOQUIMICA
  • MINERALOGIA
  • CALIDAD DE LAS AGUAS
  • EDAFOLOGIA
• Localización:  EL SERVICIO DE DOCTORADO, UNIVERSIDAD DE SEVILLA
• 2011barbaminer.pdf
• Resumen:
  INTRODUCTION AND OBJECTIVES The impact of human-induced activities is noticeable in most regions of the world, but it is particularly evident in estuaries and coastal wetlands subject to multiple environmental pressures, such as: water abstraction, industrial and domestic effluents, altered hydrology, habitat degradation and overharvest of resources. The Huelva estuary, on the southwestern coast of Spain (Gulf of Cádiz), is considered one of the most polluted estuaries in Europe, as a result of the acid mine drainage and disposal of industrial processing wastes. This estuary receives very acidic (pH values below 4) and heavily polluted discharges from the Odiel and Tinto rivers, after draining a large number of mining-impacted sites of the Iberian Pyrite Belt. Additionally, large amounts of industrial pollutants have been discharged since the mid-1960s from a variety of chemical factories (copper smelter, paper mill factory, phosphate fertiliser plant, chlor-alkali industry, etc.) and oil refineries. Moreover, the introduction of strawberry cultivation in the late half of the 1970s has increased the impacts on soil and water quality, due to intensive use of agrochemicals in the vast plantations that stretch over tens of square kilometres around the estuary. The Domingo Rubio wetland forms a part of the Marismas del Odiel Natural Park at the estuary of Huelva. It consists of a typical marshland system subjected to the tidal action in its low sector, whereas the upstream area has been transformed into a lagoon due to anthropogenic influences. The tideland zone is connected to the estuary through a tidal channel across a salt-marsh wetland developed in a small flooded valley, which is incised into a deeply kaolinized paleosurface of Plio-Pleistocene age. Soils and sediments developed in the tidal-affected area of the wetland preserve nowadays the effects of multi-source pollution problems derived from a variety of human activities, mainly metallurgical, industrial and agricultural land uses. In this study, a representative selection of samples of abiotic components (soils, sediments and waters) of the Domingo Rubio ecosystem were analyzed in order to determine mineralogical and geochemical factors governing enrichment, fractionation, mobility and environmental fate of potentially toxic trace elements. The aims of this research can be summarized in some points: 1. To identify the most prominent and active sources of pollution in the area. 2. To determine composition, properties and environmental quality parameters of soils, sediments and waters. 3. To establish a model of trace element fractionation among the geochemical and mineralogical fractions of the soils and sediments, by means of an optimized sequential extraction procedure. 4. To predict the possible environmental fate of the trace elements under hypothetic situations (flooding, oxidation, acidification), and chemical speciation in aqueous solution of the most labile trace elements. 5. To quantify the mobile and potentially mobile fractions of trace elements of environmental concern. 6. To propose corrective actions to reduce the environmental pollution effects in the area. MATERIALS AND METHODS Materials Forty-one water samples were taken from the tidal channel, lagoon and tributaries, in two sampling campaigns, one of them during high tide in summer, and the other during low tide in winter. In situ hydrochemical parameters (pH, Eh, electrical conductivity and dissolved oxygen) were measured before filtration though a 0.45 micron pore-size filter. Twenty-eight sediment samples from 13 sampling points were also collected. Eighteen of the samples were from 7 short cores (20 cm depth) obtained in the borders of the tidal channel (14 samples) and lagoon (2 samples), and from the bottom of tributaries (2 samples). All the sediment cores showed redoximorphic features identified by the presence of oxidized and reduced states of iron. The rest of the samples were surficial sediments taken at the same environments. Two soil sampling programs were conducted. The first one was designed to obtain representative samples of the dominant soil groups in the area and some Technosols of great environmental concern. Most soil samples were taken by auger at two depth levels (0-10 cm and 10-20 cm). The second sampling campaign (12 soil cores) was more precise and focused on Fluvisols, which are the most representative soils in the tideland area. The sampling sites were situated in the vicinity of the mouth area, in the low marsh with scarce vegetation, in the vegetated low marsh and in the vegetated high marsh. In addition, 15 salt efflorescences samples were collected from a Technosol developed on mine spoils containing metallic sulphides, and from soils exposed to runoff from industrial areas. Methods The water samples were analyzed for alkalinity by titration, for phosphates by colorimetry, and for bromide, chloride, nitrate, nitrite and sulfate by ion chromatography. The major cations (Ca, Mg, Na and K) were analyzed by flame spectroscopic methods (AAS and AES), and the trace elements concentrations were determined by ICP-MS. The Life Cycle Impact Assessment (LCIA) was applied over the nutrient concentrations determined in waters, in order to establish the category Aquatic Eutrophication and to quantify the eutrophication potential of N and P compounds. The soil and sediment cores were divided into several samples based on texture and coloration differences. The samples were dried, disaggregated, sieved to recover the <2 mm fraction, homogenized and splitted into aliquots for further analyses. The samples for chemical analysis were ground in an agate mortar and sieved to a grain size less than 63 micron. Physic-chemical parameters, including pH, Eh, electric conductivity and color were determined following routine laboratory procedures. Particle size distribution was determined by using a laser diffraction particle size analyzer (Mastersizer). Total organic matter content derived from the organic carbon determined by the Walkley-Black method; the carbonate content was obtained with the Bernard calcimeter, and the total S and C concentrations were measured using a LECO analyzer. Soluble salts were extracted with deionized water and the extracts were analyzed by ion chromatography (for anions) and AAS (for major cations). Cation exchange capacity was determined using a method based on the Cu-triethylenetetramine complex. Mineralogical analyses of the whole sample and the <2 micron fraction were carried out by conventional methods of XRD. Selected samples were examined by SEM-EDS in order to identify amorphous and accessory phases on back-scattered electron images. Chemical analyses of the whole sample were done by XRF on pressed powder pellets (for major elements) and fused pearls (for a suite of trace elements including As, Cd, Co, Cr, Cu, Ni, Pb and Zn). Single extraction procedures were conducted in order to assess the mobile (water-soluble and CaCl2-extracted) and potentially mobile (EDTA-extracted) fractions of trace elements in soils. Two sequential extraction schemes were also employed for determining chemical partitioning of trace elements into the following operationally-defined fractions: soluble-exchangeable, carbonate, poorly-crystallized Fe oxy-hydroxides, crystalline Fe oxy-hydroxides, Fe oxides and sulfides. Trace element concentrations in all the extract solutions were measured by ICP-AES. Interstitial waters were extracted from the Fluvisols by centrifugation, and analyzed by AAS for trace elements. Selected samples of the Technosol developed on mine spoils were subjected to oxidation experiments using four different oxidizing agents (ultrapure water, marine water, KNO3 and FeCl3¿ 6H2O) for contact periods of 3, 24 and 48 hours, and 7 days. The leach solutions were analyzed by AAS for trace elements. An aliquot of the efflorescent salts was solubilized with deionized water, and analyzed for trace elements by ICP-OES. The aqueous solutions were geochemically modeled with the PHREEQC code (database WATEQ4) to predict chemical speciation of trace elements and minerals saturation indices. Another aliquot was used for mineralogical analyses by DRX and SEM-EDS. The experimental results were treated with the software StatSoft Statistica 7.0 to recognize geochemical associations, and temporal and spatial trends for physico-chemical parameters and elemental concentrations in water, sediments and soils. Statistic analyses included descriptive statistics, normality tests, cluster analysis and principal component analysis. RESULTS AND DISCUSSION The estuarine waters are slightly alkaline and oxidizing, with pH values ranging from 7.2 (low tide) to 7.8 (high tide) and mean Eh value of +380 mV, with the exception of acidic values recorded at the mouth of the tidal channel under low tide conditions (pH 5.3). Some tributaries receiving leachates from abandoned sulfide wastes also showed acidic (pH 3.8 to 4.1) and oxidizing (Eh +585 mV) conditions. In the lagoon, the mean pH varied depending on the season (7.5 in summer and 8.4 in winter), and the Eh was as low as +225 mV. The electrical conductivity (EC) of water declined gradually in the upstream direction, from 47.5 mS cm-1 (estuarine zone) to values around 1 mS cm-1 (lacustrine zone), thus reflecting the tidal interaction effect. EC values reached up to 28.5 mS cm-1 in the temporary floodplain pond affected by acid leachates from nearby sulfide wastes. A cluster analysis showed great affinity between hydrochemical master variables (pH, Eh and salinity), marine ions (Na+, Mg2+, Ca2+, K+, Cl-, Br- and SO42-) and dissolved chalcophile elements (Fe, Cu, Zn, As and Cd) that exceed, at least, in one order of magnitude the normal values for natural waters. This group defines the waters quality coming from the mine-contaminated estuary of Huelva. However, the largest amounts of trace elements were confined to some well-defined stream tributaries affected by acid spills from an abandoned chemical plant (up to 168 microg L-1 of Cu; 33.6 microg L-1 of Zn; 4.37 microg L-1 of Cd; 1.54 microg L-1 of Mn; 770.5 microg L-1 of Ni; 267.2 microg L-1 of Co; 219.1 microg L-1 of As; and 198.3 microg L-1 of Pb). Very high concentrations of heavy metals, especially Cu, Pb and Zn, were also found in the stream waters draining sulphide-bearing mine and industrial wastelands. With regard to nutrient anions, the quantity of phosphate in the estuarine water was significantly greater at high tide than at low tide, and decreased upstream from 4.1 mg L-1 to 0.7 mg L-1 following a longitudinal gradient along the tidal channel. Instead, nitrate distribution showed an opposite trend, with values ranging from less than 0.3 mg L-1 (mouth area) to 25 mg L-1 (upper course). In terms of eutrophication, N is the limiting factor during high tide, being P during low tide. Nevertheless, the highest levels of phosphate (up to 18.5 mg L-1), nitrate (up to 96.8 mg L-1) and nitrite (up to 1.82 mg L-1) and, therefore, the maxima eutrophication potentials, were detected in small streams that drain agricultural landscapes. The sediments showed circum-neutral mean pH values, with extreme values ranging between 4.33, recorded in the bottom of the stream which flows near the abandoned chemical plant and 8.04 at the lagoon margin. Higher variations were found in the electric conductivity, from non-saline (0.12 mS cm-1) to extremely saline conditions (26.4 mS cm-1). Slightly oxidizing conditions, with an average Eh value of +352 mV, are prevalent in the estuarine environment, whereas the non-tidal sediments are usually under slightly reducing conditions (Eh< +300 mV). In general, sediments varied from lime to sand in particle size, with low clay content. Organic carbon content reached up to 5.21%, although values were below 2% in most of the samples. Concentrations of soluble ions in sediments of the tidal channel border were higher than those of the continental sediments, especially for marine ions (Na+, Cl-, Br-, SO4=). Cation exchange capacity (CEC) varied widely from 1.5 to 77.3 cmol(c)kg-1, the extreme values being noted for continental sediments, and base saturation was higher than 50%, except for acid sediments in which H+ and Al3+ are the dominant ions in the exchange complex. Mineralogical composition of the bulk sediments consisted basically of quartz, phyllosilicates and feldspars, the first being predominant in lagoon and stream samples, and the latter in tidal sediments. Goethite, hematite, halite, gypsum, and locally vivianite and jarosite, were the most common accessory minerals. The clay fraction was generally composed of kaolinite and illite, and locally, in a lesser extent, smectite, vermiculite and poorly defined mixed-layer phases. The whole-sample chemistry is clearly dominated by SiO2 (mean 61.9 %) with minor amounts of Al2O3 (15.8%) and Fe2O3 (8.22%), reflecting the mineral composition of the sediments. Mean concentrations of Zn (866.4 mg kg-1), Cu (783.6 mg kg-1), As (425.0 mg kg-1) and Pb (405.8 mg kg-1) were significantly high when compared to the local background, thus suggesting a strong enrichment of such potentially toxic trace elements in sediments. The best represented soils in the tideland zone are Salic Fluvisols, whereas Gleyic Fluvisols are dominant in the lagoon area. Technosols are widespread soils in the industrial area, some of them (Thionic Technosols) are characterized by an extremely acid horizon in which sulphuric acid is formed through oxidation of sulphides. Other groups of soils recognized in the surroundings of the wetland are Euthric Fluvisols, Skeletic Regosols, Arenic Regosols, Calcaric Arenosols, as well as a plinthic paleosol. The soil reaction was generally slightly acid, with pH values varying from 1.98 to 9.60, with Thionic Technosols being the most acidic soils in the wetland. The electrical conductivity varied in the same range as reported previously for sediments, and the Eh values fluctuated greatly from +72.4 mV, in the hydromorphic soils of the lagoon, to +707 mV in the Thionic Technosols. The range in percentages of sand, silt and clay defined a dominant silt loam texture for Salic Fluvisols, whereas the soils unaffected by the tidal wave had higher sand percentages. The mean organic carbon content was 2%, but the acidic soils did not show organic matter, in contrast to the hyperhumic salt-marsh soils, which contained up to 8% of organic carbon. As noted for sediments, most of the soils were base-saturated with Na+ dominating the exchange complex, excluding the Thionic Technosols in which base cations are displaced by acid cations. The CEC varied from 3.12 cmol(c) kg-1 in sandy soils, to 122 cmol(c) kg-1 in salt-marsh soils. Soils have the same qualitative mineral composition as the sediments, although Salic Fluvisols showed higher proportions of clay minerals relative to quartz and feldspars. The clay mineral assemblage comprises variable proportions of kaolinite (20-75%) and illite (20-65%), with minor smectite. Quartz, feldspars and iron oxides are the main accompanying minerals. Thionic Technosols are mineralogically composed of metallic sulphides, especially pyrite, and their secondary oxidation products, mainly hematite, jarosite and gypsum. In agreement with the mineral composition, the mean SiO2 content in Salic Fluvisols (44.3%) was clearly lower than that of the remaining soils (64.6%), whereas the Al2O3 content showed an opposite abundance pattern. The Fe2O3 percentage reached up to 10.1% in the Fluvisols, although the maximum value was found in the Thionic Technosols (25%) due to the abundance of iron-rich phases. Geochemical anomalies from background geochemical values were detected in Salic Fluvisols for trace elements such as: Zn (2798 mg kg-1), Cu (2651 mg kg-1), Pb (849 mg kg-1) y As (up to 675 mg kg-1). These chalcophile elements are strongly enriched in the salt-marsh soils of the mouth area, and particularly in the technogenic soils developed on pyrite-rich mine spoils. These potentially contaminated soils showed high enrichment factors (up to 2211 for Pb, 436 for Cu, 318 for As and 113 for Zn) and geoaccumulation indices (8.45 for Pb, 6.10 for Cu, 5.65 for As and 4.16 for Zn), and therefore it would be recommendable a site-specific risk assessment, according to the current Spanish regulation on contaminated soils. A principal component analysis allowed recognizing two distinctive pedogeochemical associations: Cu-Pb-Zn-As-Cd and Cr-Ni-Co, which are interpreted as formed by anthropogenic and geogenic trace elements, respectively. Sequential chemical extractions showed that the anthropogenic trace elements in Fluvisols are mainly bound to reducible phases (As 89%, Pb 68%, Zn 57%, Cu 44%), which are in order of abundance: crystalline oxides (hematite) > crystalline oxy-hydroxides (goethite, ferrihydrite) > amorphous oxy-hydroxides. The remaining portions of these elements were geochemically partitioned among the most labile phases (up to 18% of soluble-exchangeable Cd, and 33% of carbonate-bound Cu), oxidisable phases (up to 21% of Pb) and residual phases (up to 19% of Cd). In the other hand, in the Thionic Technosols, the anthropogenic elements are mainly bounded to the oxidisable fraction (up to 90% of Zn, 80% of Cd, 70% of Cu and 20% of Pb). These proportions are traduced in high concentrations of elements, which can be highly leached under oxidizing conditions as, for example, the produced when marine water leaches the soils. Although the mobile metal fraction assessed by single extraction with CaCl2 was relatively low in Salic Fluvisols (maximum value 8.97% for Cu), significant fractions of EDTA-extracted metals (Cu 54.6%, Zn 47.5%, Pb 40.8% and As 7.30%) are potentially able to move into the plant root system. The overall mobility sequences for trace elements of concern are as follows: - Mobile elements (CaCl2-extracted): Cu > Zn >= As >> Pb - Potentially mobile elements (EDTA-extracted): Cu > Zn >= Pb >> As However, the most labile metal (water-soluble) fraction occurred in transient sulphate efflorescences developed on the surface of the anthropogenic soils. The efflorescences of the Thionic Technosols are made mainly up of ferrocopiapite with elevated levels of heavy metals (up to 6570 mg kg-1 Cu and 5350 mg kg-1 Zn), whereas the crusts of the soils affected by chemical spills are composed of chalcantite with concentrations of Cu as high as 268030 mg kg-1. These potentially toxic elements are easily released from the salt efflorescences during rainy periods with free metal ions and sulphate species being the dominant aqueous species, thus contributing to the water pollution of the wetland. CONCLUSIONS According to the objectives of this study, the most relevant conclusions obtained from this research can be resumed in some paragraphs: WATERS Domingo Rubio marshland is affected by hydrochemical contamination caused by the combined effect of multiple punctual and diffuse sources. The tidal area is periodically inundated with saline waters containing high levels of dissolved As, Cd, Co, Cr, Cu, Ni y Zn, resulting of the influx coming from the estuary of Huelva. Moreover, the tidal channel receives acid leachates from punctual sources, such as sulphide mining deposits and abandoned chemical plants, contributing to the metallic enrichment. Agriculture is an important diffuse source of pollution to the zone. Water quality is affected by high nitrate (96,8 mg L-1) and phosphate (18,5 mg L-1) concentrations, carried by the tributaries which drain the agricultural area. The tidal channel acts as a nutrient carrier to the estuary of Huelva, but receiving phosphate fluxes from the estuary as well. The phosphate aquatic eutrophication potential is higher than the nitrate one during high tide, while the contrary occurs during low tide. The continental waters do not show any clear eutrophication agent. Transport and dispersion of contaminants emitted by the multiple sources is mainly controlled by the tidal regime, with the exception of the lagoon area, where the composition of the waters is directed by a seasonal mineralization pattern. SOILS AND SEDIMENTS The predominant soils in the Natural Area are Salic Fluvisols, which show slightly acid conditions and silty-loam texture, and are essentially composed by quartz and phyllosilicates (illite and kaolinite), accompanied by minor proportions of feldspars, iron oxides and soluble salts. Locally, there have been recognized extremely acidic Thionic Technosols, composed of pyrite and its secondary oxidation products (jarosite, ferricopiapite, gypsum and Fe oxy-hydroxides). Fluvisols show geochemical anomalies in some trace elements like As, Cu, Pb and Zn, especially near the mouth of the tidal channel, in topsoil and subsoil as well. Enrichment factors reach up to 175 for As, 84.7 for Pb, 77.8 for Cu and 34.4 for Zn. Actual sediments registered similar enrichments of these elements, in the low and high course, and in some tributaries. Nevertheless, the most significant anomalies have been detected in the Thionic Technosols, showing enrichment factors up to 2211 for Pb, 436 for Cu, 318 for As and 113 for Zn. The geochemical association As-Cu-Zn-Pb is statistically significative (alpha < 0.05) and reflects the anthropic origin, while the rest of trace elements (Co-Cr-Ni) constitute a lithogenic association. Most of the studied soils can be classified from moderate to extremely contaminated with Cu, Zn As and/or Pb, according to the international scale of the geoaccumulation index. For this reason, the problematic soils should be studied in terms of a risk analysis to establish the necessity of decontamination or not. Trace element enrichment in Fluvisols and tidal sediments is mainly attributed to the interaction of the estuarine water with the more reactive components of the soil, which explains that in the lagoon area the soils show trace elements concentrations similar to the background values. The anthropogenic trace elements are mainly associated with reducible phases (As 89%, Pb 68%, Zn 57%, Cu 44%). These phases are, in order of abundance: crystalline oxides (hematite) > crystalline oxy-hydroxides (goethite, ferrihydrite) > amorphous oxy-hydroxides. The remaining proportions of these elements are distributed among the most labile phases (soluble, exchangeable and carbonates), oxidisable phases and residual phases. According to the results obtained from the CaCl2 extractions (mobilizable fraction) and EDTA (potentially mobilizable), the next relative mobility sequence can be established in the Salic Fluvisols: Mobile elements: Cu > Zn > As > Pb Potentially mobile elements: Cu > Zn > Pb > As The soil components which mainly participate on the trace element retention are the Fe-oxy-hydroxides and clay minerals, by means of adsorption, coprecipitation and ionic exchange processes, according to the salinity, Eh and pH conditions. Thionic Technosols are capable of leaching high concentrations of Zn, Cu and Pb (up to 292, 132 and 11.2 mg kg-1 respectively), according to the oxidation experiences taken along with marine waters, so they would represent the main contamination source to the soils of the wetland. EFFLORESCENCES Two types of soluble salt efflorescences have been identified over the soils and sediments affected by anthropic activities, which differ on their characteristics and composition of those natural efflorescences of the marshland. ¿ Thionic Technosols present yellowish sulfated efflorescences, composed essentially by copiapite, jarosite and gypsum, with high concentrations of potentially toxic elements(6570 mg kg-1 of Cu, 5350 mg kg-1 of Zn, 380 mg kg-1 of As and 18.3 mg kg-1 of Cd). ¿ Soils around the stream which drains an abandoned Cu-sulphate plant are covered by greenish and bluish efflorescences, composed by copper sulfates and chlorides respectively, containing up to 268g kg-1 of Cu, 82.2 g kg--1 of Zn, 5180 mg kg-1 of Al, 40.3 mg kg-1 of As and 17.5 mg kg-1 of Pb. These efflorescences precipitate during dry periods due to evaporation of the acid leachates and are easily dissolved by the rain effect, thus contributing to the acidification and contaminations of Domingo Rubio waters with sulfates and heavy metals.