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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Journal of Geochemical Exploration 123 (2012) 143–151 Contents lists available at SciVerse ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp Time and space variations in mercury and other trace element contents in olive tree leaves from the Almadén Hg-mining district P. Higueras a,⁎, J.A. Amorós b, J.M. Esbrí a, F.J. García-Navarro b, C. Pérez de los Reyes b, G. Moreno b a Instituto de Geología Aplicada-Laboratorio de Biogeoquímica de metales pesados, Universidad de Castilla-La Mancha, Pl. Manuel Meca 1, 13400 Almadén (Ciudad Real), Spain b Instituto de Geología Aplicada, Escuela de Ingenieros Agrónomos de Ciudad Real, Universidad de Castilla-La Mancha, Ronda de Calatrava 7, 13071 Ciudad Real, Spain article info abstract Available online 9 May 2012 Olive trees (Olea europaea, L.) are a very important agricultural resource for Spain in general and for the Castilla-La Mancha region in particular. These trees provide significant amounts of olive oil and olives for di- Keywords: rect consumption. In this paper we discuss analytical constraints regarding the uptake of metallic trace ele- Mercury ments from soils and other sources for olive-trees growing in the Almadén mercury mining district, the Metallic trace elements world's largest producer of this element, which is currently inactive. The study was based on the analysis Olive tree leaves of these metals in soils and sets of olive trees of different ages from seven sites located at different distances Soils from the main mercury sources. The results show good correlations between soil and leaf contents for major Almadén Spain elements from the soils (Fe, Al, Mg and Ca), but very little or no relationship between metallic trace elements in soils and leaves. However, bioavailable mercury in the soil does correlate well with leaf contents, indicat- ing a significant uptake of this fraction. Furthermore, detailed analysis of the temporal evolution of mercury contents in leaves compared with the temporal evolution of local atmospheric mercury contents, which de- creased dramatically in recent years due to the reclamation of the main dump of the mine, indicates some influence of this parameter on the incorporation of mercury in the leaves and suggests a possible mechanism of atmospheric uptake of the element. Mercury contents in local olive oil and olives are slightly higher for samples taken from areas with also higher mercury concentrations in soils, but levels are well below maxi- mum recommended levels for human food. © 2012 Elsevier B.V. All rights reserved. 1. Introduction describe high to very high mercury contents in soils at the regional scale; in particular, Conde et al. (2008) study a transect of mercury 1.1. The study area contents in soils from the Almadén periurban area and find mercury concentrations that point out to the element as a pollutant agent for The Almadén mercury mining district is located in the Castilla-La drainage waters. Díez et al. (2011) studied mercury contents in the Mancha region in South-Central Spain (Fig. 1). This area corresponds hair from inhabitants of the area and found slightly higher values to the biggest mercury geochemical anomaly in the world and has for inhabitants of Almadén compared to those in surrounding areas, yielded almost one third of the total global production of this element thus indicating a certain health risk. (Hernández et al., 1999). Descriptions of the geological characteristics From the physiographic point of view, the Almadén area is of the area can be found in reports by Saupé (1990) and Hernández et characterised by an Appalachian relief, meaning a landscape domi- al. (1999), among others, while Lindberg et al. (1979), Huckabee et al. nated by long ‘sierras’ and narrow valleys that follow approximately (1983), Higueras et al. (2003), Millán et al. (2004, 2006, 2011), the E–W geologic structural trends; the ‘sierras’ correspond to quartz- Molina et al. (2006), Moreno-Jiménez et al. (2006), Martínez- ite outcrops and the valleys to shale-dominated geological formations Coronado et al. (2011) have described environmental concerns re- (Fig. 1). As a semiarid area, with precipitation in the range garding mercury in the area and include local soil/plant relationships. 550–700 mm/year, dry farming agriculture and livestock dominate In particular, Molina et al. (2006) reported mercury contents in olive the activities in the valleys and the ‘dehesa’ (Spanish term for the re- tree leaves, which is the main aspect discussed in this paper. Gray et gionally characteristic landscape of smooth plains and hills with tree al. (2004), Higueras et al. (2003, 2006) and Conde et al. (2008) vegetation dominated by oak trees, Querqus ilex), is the predominant landscape. Olive trees (Olea europaea, L.) are also quite common and these correspond to ‘sierra’ varieties and, in particular, to the ‘ ’ fi ⁎ Corresponding author. Cornicabra variety. Local soils have been classi ed as Cambisols E-mail address: [email protected] (P. Higueras). (Leptic or Chromic) (Conde et al., 2008). 0375-6742/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2012.04.012 Author's personal copy 144 P. Higueras et al. / Journal of Geochemical Exploration 123 (2012) 143–151 Fig. 1. Location of the study area. The Castilla-La Mancha region is shadowed. Locations mentioned in Table 1 are all shown in this scheme. 1.2. Olive trees, soils and heavy metals It is widely accepted that 17 major and trace elements (Al, B, Br, Cl, Co, Cu, F, Fe, I, Mn, Mo, Ni, Rb, Si, Ti, V and Zn) are essential for plants; The olive is a perennial leaf tree that has been cultivated for cen- it has been proved that some of these are necessary only for certain turies. Nowadays, there are more than 8 million ha producing olives species, whereas others only have stimulating effects for plant in the world and most of these are located around the Mediterranean growth, but their functions have not yet been identified (Wild, Basin. In Spain there are more than 2 million ha with more than 1992). Other elements seem to be not needed at all and are toxic to 300 million trees. Moreover, Castilla-La Mancha is the second largest plants: Hg, Cu, Ni, Pb, Co and Cd and also possibly Ag, Be and Sn. region in Spain (below Andalucía) in terms of hectares dedicated to The olive tree is a pluriannual leaf tree and bears leaves from three olive culture, with 300,000 ha approximately (Barranco et al., 2004). different years. Some previous data on metallic element contents in It is well known that leaf analysis must be based on standardised these leaves have been reported (Bargagli, 1995; Gascó and Lobo, sampling methods and that results must be compared only with stan- 2007; Madejón et al., 2006) and data for fertilisation programmes dard values obtained by those procedures. Standard values for olives has been published (Bould, 1966; Fernández-Escobar et al., 1999; have been compiled by Fernández-Escobar et al. (1999) based on data Vavoulidou et al., 2004). In general terms, the behaviour of these ele- reported by Bould (1966). ments in leaves with time corresponds to three different models: Several studies have been carried out in Mediterranean regions and areas of influence to investigate soil origins, parent materials A. Accumulation with time. This behaviour corresponds to structural and their characteristics (Amorós et al., 2010; Carlevalis et al., elements (Bould, 1966; Fernández-Escobar et al., 1999) and to el- fi 1992). Indeed, recently published studies have focused on the area ements that are dif cult for the plant to excrete. This behaviour under consideration in this paper (Conde et al., 2009; De la Horra et has been previously described for Ca (Bould, 1966; Fernández- al., 2008). The study of geochemical soil composition provides infor- Escobar et al., 1999) and Ni (Madejón et al., 2006). mation, along with other complementary data, about fertility and B. Decay in content with time. This model corresponds to essential the availability of nutrients for plants. Major elements provide infor- elements that are necessary for the plant metabolism. Contents mation about total structural components and potential nutrients are therefore higher in young leaves and decay with time (Bould, (Lanyon et al., 2004; White, 2009; Wild, 1992). On the other hand, 1966; Fernández-Escobar et al., 1999). Some potentially toxic ele- contents of trace elements give an insight into the geochemical origin ments such as Pb, Zn and As show this behaviour (Madejón et al., (García-Navarro et al., 2009) and potential toxicity (Conde et al., 2006). 2009; García-Navarro et al., 2009; Patra and Sharma, 2000) of the soil. C. Constant elements. This behaviour corresponds to elements that The metabolism of trace elements in plants has been widely stud- have approximately constant concentrations in leaves. Mn and ied (Kabata-Pendias, 2001; Wild, 1992). However, every plant–soil Cu correspond to this model (Madejón et al., 2006). system has to be specifically studied, since the behaviour could differ depending on the elements present in a particular system (Kabata- This work describes and discusses the distribution of mercury in Pendias, 2001; Molina et al., 2006) as well as on the particular chem- olive tree leaves in the heavily contaminated area and surroundings ical form of the element in the soil.