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Bioavailability and chronic toxicity of metal sulfide minerals to benthic marine invertebrates: implications for deep sea exploration, mining and tailings disposal Stuart L Simpson, and David Spadaro Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00203 • Publication Date (Web): 03 Mar 2016 Downloaded from http://pubs.acs.org on March 4, 2016
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Bioavailability and chronic toxicity of metal sulfide minerals to benthic marine
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invertebrates: implications for deep sea exploration, mining and tailings disposal
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Stuart L. Simpson*, David A. Spadaro
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Centre for Environmental Contaminants Research, CSIRO Land and Water, Sydney, NSW 2234, Australia
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* To whom correspondence may be addressed: CSIRO Land and Water, Sydney, NSW 2234, Australia Phone: +61 2 97106807 Email:
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TOC Art
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ABSTRACT
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The exploration and proposed mining of sulfide massive deposits in deep-sea environments and
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increased use deep-sea tailings placement (DSTP) in coastal zones has highlighted the need to
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better understand the fate and effects of mine-derived materials in marine environments. Metal
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sulfide ores contain high concentrations of metal(loid)s, of which a large portion exist in highly
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mineralised or sulfidised forms and are predicted to exhibit low bioavailability. In this study,
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sediments were spiked with a range of natural sulfide minerals (including chalcopyrite,
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chalcocite, galena, sphalerite) to assess the bioavailability and toxicity to benthic invertebrates
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(bivalve survival and amphipod survival and reproduction). The metal sulfide phases were
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considerably less bioavailable than metal contaminants introduced to sediment in dissolved
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forms, or in urban estuarine sediments contaminated with mixtures of metal(loid)s. Compared to
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total concentrations, the dilute-acid extractable metal(loid) (AEM) concentrations, which are
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intended to represent the more oxidised and labile forms, were more effective for predicting the
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toxicity of the sulfide mineral contaminated sediments. The study indicates that sediment quality
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guidelines based on AEM concentrations provide a useful tool for assessing and monitoring the
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risk posed by sediments impacted by mine-derived materials in marine environments.
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Keywords: Mining, tailings, deep-sea disposal, toxicity, sediment quality guidelines
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INTRODUCTION
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In response to the growing demand for minerals, there is increased interest in exploiting high
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grade ores from deep-sea environments,1,2 and in using deep-sea tailings placement (DSTP) for
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the disposal of large volumes of mine wastes,3-5 together with increased shipping of ores and
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concentrates in marine environments.6 Sulfide massives on the seafloor and on land are
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frequently the target of mining operations due to the high concentrations of metals such as Cu,
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Pb, Zn and other precious metals. Although the procedures for mining, tailings waste disposal
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and ship loading and transport of ores and concentrates will be designed to minimise impacts, the
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process of quantifying the risks posed by metal sulfide minerals in the marine environments is
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complex.4,7-12
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The planned disposal of mine tailings in coastal environments, or spillage of metal-rich
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ores or concentrates during shipping, may result in sediments being impacted by metals and
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metalloids at concentrations that exceed sediment quality guideline values (SQGVs).13, 14
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However, it is well recognised that total concentrations of metal(loid)s in sediments are often
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poor predictors of the risk posed by these contaminants.15-17 Metal(loid)s associated with sulfide
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phases generally exhibit low bioavailability,18-21 but upon deposition in the marine environment
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may transform into more bioavailable forms, e.g. through the oxidation of sulfide phases.22,23
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The fine particle size of most mine-derived materials (e.g. mean tailings particle size typically
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with 50-200 µm range) influences both the fate (e.g. rate of deposition and resuspension) and
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bioavailability of metals in these materials (e.g. metal(loid) release and dietary exposure routes).
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Metal(loid)s may be released to the dissolved phases or partition to other sediment phases such
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as particulate organic carbon (OC) and iron and manganese oxyhydroxide phases that also
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modify the bioavailability to benthic organisms.24-26
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A large portion of the metal(loid)s within ores, tailings, and concentrates exist in highly
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mineralised or sulfidised forms that are expected to be less bioavailable to organisms when
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compared to metals introduced to the environment from other common anthropogenic sources.
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Therefore, the assessment of bioavailability is essential when developing guidelines and
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evaluating the risks posed by these materials in sediments.17,27-29 In this study, the bioavailability
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and toxicity was assessed of sediments contaminated with chalcopyrite (CuFeS2), chalcocite
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(Cu2S), galena (PbS), sphalerite (ZnS), a mixed-metal sulfide mineral, and a copper concentrate.
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Toxicity to two benthic invertebrates was assessed: survival of the bivalve Spisula trigonella,
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and survival and reproduction of the amphipod, Melita plumulosa. No standardised whole-
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sediment toxicity tests exist that utilise deep-sea organisms, so the use of these surrogate
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organisms was justified owing to the relatively high sensitivity of the test endpoints to
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metals.24,30 Bivalve molluscs and crustaceans, including amphipods, are common in many deep-
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sea environments. The bioavailability and toxicity of mineral-associated metals was compared
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with that observed with sediments spiked with dissolved copper and urban coastal sediments
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contaminated with mixtures of metal(loid)s.
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The hypothesis was that the more highly mineralised or sulfidised the metal(loid)s were,
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the less bioavailable they would be, resulting in lower risk of adverse effects to benthic
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organisms. To assist in interpreting the metal(loid) bioavailability and exposure routes
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contributing to any observed adverse effects, measurements were made of dissolved metal(loids)
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in the overlying waters and pore waters, and of dilute-acid extractable concentrations in the
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sediments, along with acid-volatile sulfide (AVS), OC, iron and manganese, and sediment
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particle size that may influence bioavailability. The appropriateness of existing SQGVs and how
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metal bioavailability considerations may improve the assessment of the risks posed by mine-
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derived materials in marine environments are discussed.
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MATERIALS AND METHODS
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General methods. All glass- and plastic-ware for analyses were usually new and were cleaned
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by soaking in 10% (v/v) HNO3 (BDH Analytical Reagent grade) for a minimum of 24 h,
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followed by thorough rinsing with deionized water (Milli-Q, 18 MΩ·cm). All chemicals were
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analytical reagent grade or equivalent analytical purity. Water pH, salinity, temperature, and
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dissolved oxygen measurements were made with probes calibrated according to manufacturer
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instructions (WTW). Methods for measurement of sediment particle size (by wet sieving
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through 63 µm nylon sieves followed by gravimetry), total organic carbon (OC, Dohrmann DC-
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190 TOC analyzer, Teledyne Tekmar), and porewater (PW) (extraction under nitrogen by
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centrifugation (800 g for 5 min) and immediate filtration to minimize oxidation) have been
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described previously.31 The pore water and overlying water samples were membrane filtered
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(0.45 µm, Sartorius Minisart) and acidified with concentrated HNO3 (2% (v/v) (Tracepur,
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Merck). Dissolved ammonia was analysed colorimetrically using a Merck Spectroquant Kit
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(14752).
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Methods for analyses of total recoverable metals (TRM, by microwave-assisted aqua
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reqia), dilute-acid extractable metals (AEM, 1 M HCl), and acid-volatile sulfide (AVS) (all
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determined on subsamples of the same homogenized sediment) are described previously.32
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Dissolved concentrations of metals and metalloids (metal(loid)s) in waters and acid digests were
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analysed by a combination of inductively coupled plasma-atomic emission spectrometry (ICP-
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AES, Varian 730-ES) and inductively coupled plasma-mass spectrometry (ICP-MS, Agilent
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7500ce). As part of the quality assurance, analyses of filter and acid-digest blanks, replicates for
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20% of samples, analyte sample-spikes, and certified reference materials (CRMs) were
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performed. Replicates were within 20%, and recoveries for spikes and CRMs, PACS-2 for
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sediment (National Research Council Canada, NRCC) were within 85−115% of expected values.
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The limits of reporting for the various methods were less than 10% of the lowest measured
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values.
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Test media and metal-mineral spiking. Clean seawater was collected from Port Hacking,
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Sydney, Australia, membrane filtered (0.45 µm), and acclimated to a room temperature of
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21±1°C. Where necessary, the salinity of the filtered seawater was adjusted to the test salinity of
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30‰ using Milli-Q water. A silty sediment (98%
