The use of a Weight-of-Evidence approach to address sediment quality in the Odiel River basin (SW, Spain)

https://doi.org/10.1016/j.ecoenv.2016.07.010Get rights and content

Highlights

  • The integrated WOE approach determines the pollution degree in the IPB.

  • FSQVs are calculated for prediction of freshwater sediment toxicity in the IPB.

  • The Asian clam as a tool for pollution assessment of AMD affected environments.

Abstract

The fluvial systems of the Iberian Pyrite Belt (SW Iberian Peninsula) are affected by acid mine drainage (a lixiviate residue product of mining activities derived from sulfide oxidation). The high acidity and high concentrations of sulfates and metal(loid)s are the main causes of the environmental degradation of the Odiel River basin. The use of weight of evidence approach in areas of the Odiel River basin implies the integration of different lines of evidence (chemistry, toxicity and bioaccumulation) using the freshwater clam Corbicula fluminea as target species.

The integration of the results from the application of the different lines of evidence showed that the index of pollution was higher downvalley (Ptriad=12,312), moderate after mining effluent discharges (Ptriad=13.9) and very low where the Odiel River sources (Ptriad=6.31). The multivariate analysis indicated that variables and chemicals were associated with geochemical matrix and background levels (% of fines and toxic metal(loid) concentrations), toxic effects, and metal(loid) bioaccumulation reflecting the geographical distribution of the contamination towards the estuary. Metal(loid) thresholds were calculated for the study area as site-specific values of interim freshwater sediment quality values: As≥171; Cd≥0.48; Co≥8.82; Cr≥38.4; Cu≥451; Ni≥18.4; Pb≥377; Sb≥17.7; Zn≥221 mg/kg of freshwater fluvial dry sediment. These results revealed the possibility of using the TEL values proposed by the USEPA and the NOAA for sediments from this site, and proposed lower PEL values for the Iberian Pyrite Belt as result of toxicity effects found in the Asian clam due to the combination of extreme acidity and high metal(loid) concentrations.

Introduction

The European Water Framework Directive (WFD) requires member states to assess the ecological quality status (EQS) of water bodies and to achieve “good water status” for all European waters by 2015 (EEC, 2000). Freshwater sediment quality values are required to protect the environment, and consequently, the public health (DelValls and Chapman, 1998). In spite of the freshwater sediment quality benchmarks are not established, most of the studies use the thresholds of the US Environmental Protection Agency (USEPA) in order to determine the level of toxicity caused by some metal(loid) concentrations in sediment. On the other hand, sediment quality values (SQVs) should be site-specific, as the National Oceanic and Atmospheric Administration (NOAA) recommends, because they are based on target species to determinate toxicological effects of chemicals. DelValls et al. (1998a) developed a quantitative Weight-Of-Evidence (WOE) approach that has been optimized and applied in the last years in different aquatic ecosystems (Choueri et al., 2009, Martín-Díaz et al., 2008a, Martín-Díaz et al., 2008b, Morales-Caselles et al., 2009, Riba et al., 2004a, Riba et al., 2004b). This is a concept/model based on integration of the results of different studies including ecotoxicological data; in-situ observations over sediment-based population changes, etc. to derive comprehensive, integrated management decision about sediment quality. These integrative studies are the result of different methodologies: i) the sediment quality triad (Chapman, 1996); ii) statistical multivariate analyses techniques (Principal Component Analyses, PCA) (DelValls and Chapman, 1998); iii) Tabular tables (Riba et al., 2004a). Yet, the use of multivariate analyses approach allows to derive site-specific ranges of concentration delimits of chemicals associated with adverse effects denominated SQVs.

The geology and the mining activity are the major pressures of the environmental status of the fluvial systems from the Iberian Pyrite Belt (IPB, Fig. 1). The IPB, in the SW of the Iberian Peninsula, is one of the largest sulfide massive deposits of the world with original reserves in the order of 1,700 Mt of sulfide ore (Sáez et al., 1999). The geological characterization determines three lithological groups belonging to the Upper Paleozoic: i) Phyllite-Quartzite Group (PQ) formed by sequences of shales and sandtones; ii) the Volcano-Sedimentary Complex (CVS), which includes a mafic-felsic volcanic sequence interstratified with shales; and iii) the Culm Group in which shales, sandstones and conglomerates prevail (Neihlig et al., 1998; Sáez et al., 1999, Tornos, 2006). Among the sulfide deposits, pyrite (FeS2) is the main mineral followed by minor chalcopyrite (CuFeS2), arsenopyrite (FeAsS), sphalerite (ZnS) and galena (PbS). Due to this metal richness, long-term mining activities occur since ancient times (Nocete et al., 2005). Although large-scale exploitation started after the Industrial Revolution and ceased in the early XIX century, mineral demanding calls for the opening/re-opening of abandoned mines nowadays. The oxidation of sulfide deposit minerals is the main environmental problem associated with the fluvial systems of the IPB (Cánovas et al., 2007, 2014; Nieto et al., 2007, Nieto et al., 2013, Sarmiento et al., 2009). This acid lixiviate, named acid mine drainage (AMD), contaminates more than the 40% of the Odiel-Tinto network (Sarmiento et al., 2009) with high concentrations of sulfates, metals and metalloids next to the estuaries (Olías et al., 2006). Sediments act as sink of these contaminants and a source of metal(loid)s in the estuary (Nieto et al., 2007). Some of the hydrochemical parameters of the Odiel River were reported with mean pH values of 3.7, electrical conductivity of 1 mS/cm and concentration of toxic elements (in mg/L): 643 SO42−, 33 Al, 11 Zn, 8 Mn, 6 Cu and 5 Fe (Nieto et al., 2007). High concentrations of sulfides and elevated turbidity and conductivity, coupled with a low pH in the IPB, seem to be the main causes of the decline in native freshwater mollusk biodiversity (Pérez-Quintero, 2011). These characteristics create an extreme environment where benthic and pelagic of macrobiota are unable to survive, limiting life just to extremophile organisms. Indeed, in-situ observations of benthic organisms are rather difficult to carry out in such an extreme environment. What is more, the results in terms of ecological indicators into the sediment quality assessment would be inconsistent through the WOE approach.

The freshwater clam Corbicula fluminea, known as Asian clam, was selected as target organism for toxicity bioassays. In spite of this is an invasive species into the Iberian Peninsula (Pérez-Quintero, 2008), it has not been found yet in the Odiel River basin. Nevertheless, it was used in previous monitoring studies for AMD (Bonnail et al., 2016, Soucek et al., 2001) and other metal polluted environments (Abaychi and Mustafa, 1988, Bilos et al., 1998; Doherty et al., 1990; Shoults-Wilson et al., 2009, Shoults-Wilson et al., 2010).

The main objective of this study is to assess the sediment quality by means of the integration of multiple lines of evidence. A WOE approach allows identifying the impacted areas by measuring the metal(loid) concentration from different segments of the Odiel River basin, sediment toxicity bioassays and the bioaccumulation of metal(loid)s in soft tissue of the Asian clam. The classical sediment quality triad (SQT) study allows assessing the environmental degradation by comparing the sediment quality along Odiel River with other neighboring non polluted ecosystem. This integration permits to calculate the SQVs by linking both chemical and biological measurements using the multivariate analysis.

Section snippets

Sampling

This study was developed within three stations into the IPB along the Odiel River basin, where the river sources (O1), downstream first mining discharges (O2) and the lowest part of the basin downstream (O3) (Fig. 1). The first sediment sampling point (O1) was located in the upper part of the river, in the Ossa-Morena Zone, where limestone is common (Sarmiento et al., 2009). Hence, the hydrochemistry in the head of the Odiel River is characterized by Ca-Mg bicarbonate facies. The pH in water of

Chemical results

The summarized results of the sediment chemistry, toxicity and bioaccumulation used for the SQT measurements are given in Table 1. Briefly, the textural composition of the sediments consists of an increasing muddy fraction from the head towards the estuary of the Odiel River; such as result of particulate matter supply from mining effluents and loss of river energy in the lower part (14%, 25% and 45% of fines increasing downstream), i.e. formation of oxyhydroxysulphates as precipitates and

Discussion

The Odiel River basin drains materials of the IPB. This belt is a sulfide deposit unit that was mined in the past; however some of the mines are being re-opened due to the current demand of minerals. Then, the fluvial network is receiving AMD lixiviates from mining activities and residues spread over the catchment. As previously explained, the environmental degradation is mainly caused by these facts.

Based on information provided by the classical SQT representation (Fig. 3) plus the MAA results

Conclusions

The IPB is a sulfide mineral region extensively affected by mining activity; whose fluvial networks are characterized by high acidity and an important metal(loid) load (AMD). Due to that, and the lack of freshwater sediment quality values in the National legislation, it makes necessary to promptly develop assessment standards for freshwater sediment quality to highly polluted environments.

The current study presents the results and interpretation of the chemical composition and biological

Acknowledgments

The authors are grateful to the International Grant from Bank Santander/UNESCO Chair UNITWIN/WiCop. The first author thanks the Erasmus Mundus Programme for the MACOMA Doctoral funding contract (SGA 2012-1701/001-001-EMJD). We also thank the reviewers for their valuable comments.

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