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Article http://pubs.acs.org/journal/acsodf Leaching of Metals and Metalloids from Hydrothermal Ore Particulates and Their Effects on Marine Phytoplankton † † ‡ § ∥ ⊥ Shigeshi Fuchida,*, Akiko Yokoyama, Rina Fukuchi, Jun-ichiro Ishibashi, Shinsuke Kawagucci, , # † Masanobu Kawachi, and Hiroshi Koshikawa † # Marine Environment Section, Center for Regional Environmental Research and Biodiversity Resource Conservation Office, Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan ‡ Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8564, Japan § Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan ∥ ⊥ Department of Subsurface Geobiological Analysis and Research (D-SUGAR) and Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan *S Supporting Information ABSTRACT: Seafloor massive sulfide deposits have attracted much interest as mineral resources. Therefore, the potential environmental impacts of full-scale mining should be considered. In this study, we focused on metal and metalloid contamination that could be triggered by accidental leakage and dispersion of hydrothermal ore particulates from mining vessels into surface seawater. We determined the leaching potential of metals and metalloids from four hydrothermal ores collected from the Okinawa Trough into aerobic seawater and then evaluated the toxic effects of ore leachates on a phytoplankton species, Skeletonema marinoi−dohrnii complex, which is present ubiquitously in the ocean. Large amounts of metals and metalloids were released from the ground hydrothermal ores into seawater within 5 min under aerobic conditions. The main components of leachates were Zn + Pb, As + Sb, and Zn + Cu, which were obtained from the Fe−Zn−Pb-rich and Zn−Pb-rich zero-age, Ba-rich, and Fe- rich ores, respectively. The leachates had different chemical compositions from those of the ore. The rapid release and difference in chemical compositions between the leachates and the ores indicated that substances were not directly dissolved from the sulfide-binding mineral phase but from labile phases mainly on the adsorption−desorption interface of the ores under these conditions. All ore leachates inhibited the growth of S. marinoi−dohrnii complex but with different magnitudes of toxic effects. These results indicate that the fine particulate matter of hydrothermal ores is a potential source of toxic contamination that may damage primary production in the ocean. Therefore, we insist on the necessity for the prior evaluation of toxic element leachability from mineral ores into seawater to minimize mining impacts on the surface environment. 1. INTRODUCTION minerals in the epipelagic zone could damage marine fl fi phytoplankton communities at the base of the marine food Sea oor massive sul de (SMS) deposits have attracted interest 5−8 because of their potential as available mineral resources. chain. Therefore, the mobility of these metals and metalloids However, seafloor metal-mining could create new problems in hydrothermal ores should be evaluated to predict the fl in the marine environment and could have serious quantitative impacts of sea oor metal-mining on marine consequences for marine ecosystems.1,2 One of these problems ecosystems. is the potential for metal and metalloid contamination, as Various types of ore deposits are present in submarine fi 9−11 metals are easily introduced into ecosystems where they hydrothermal elds. For example, Halbach et al. (1993) fi gradually accumulate in the bodies of living organisms.3,4 found that the hydrothermal ore in the hydrothermal eld of It has been postulated that plumes of fine particulate Izena Hole, Okinawa Trough, had various chemical composi- − fi minerals that arise during mining operations could be a major tions and mineral assemblages, including Zn Pb-rich sul de source of metal and metalloid contamination.2,5 Such plumes ore, Ba−Zn−Pb sulfide ore, massive Zn−Cu-rich sulfide slabs, are generated in the benthic zone as a result of drilling ore minerals and stripping unconsolidated sediment from the Received: April 17, 2017 seafloor surface and in the epipelagic zone as a result of leakage Accepted: June 9, 2017 of crushed ore from mining vessels. Plumes of fine particulate Published: July 5, 2017 © 2017 American Chemical Society 3175 DOI: 10.1021/acsomega.7b00081 ACS Omega 2017, 2, 3175−3182 ACS Omega Article Table 1. Chemical Composition of Leachates from Ores (Means ± Standard Deviation of the Triplicate) Fe−Zn−Pb-rich ore Zn−Pb-rich zero-age ore (HPD1313G04) Ba-rich ore (HPD1313G05) Fe-rich ore (HPD1311G06) (HPD1355R04) (a) 5 min Shaking Time pH 4.3 6.8 4.8 6.7 Mn (mM) 0.0108 ±0.0002 0.0118 ±0.0009 0.17 ±0.02 0.118 ±0.005 Fe (mM) 4.9 ±0.1 0.34 ±0.02 n.d. n.d. Cu (mM) n.d.a n.d. 0.48 ±0.06 n.d. Zn (mM) 3.5 ±0.1 0.87 ±0.05 70 ±9 2.2 ±0.1 As (mM) n.d. 0.26 ±0.01 n.d. n.d. Cd (mM) 0.0103 ±0.0003 n.d. 0.19 ±0.02 0.0063 ±0.0003 Sb (mM) n.d. 0.038 ±0.002 n.d. n.d. Pb (mM) 0.224 ±0.006 n.d. n.d. 0.094 ±0.006 (b) 6 h Shaking Time pH 4.6 6.6 4.9 6.8 Mn (mM) 0.0198 ±0.0003 0.0129 ±0.0001 0.1640 ±0.0003 0.084 ±0.001 Fe (mM) 5.62 ±0.02 0.100 ±0.002 n.d. n.d. Cu (mM) n.d. n.d. 1.187 ±0.001 n.d. Zn (mM) 6.69 ±0.02 1.03 ±0.01 62 ±1 3.67 ±0.01 As (mM) n.d. 0.459 ±0.003 n.d. n.d. Cd (mM) 0.0263 ±0.0002 n.d. 0.188 ±0.001 0.01376 ±0.0001 Sb (mM) n.d. 0.101 ±0.001 n.d. n.d. Pb (mM) 0.231 ±0.001 n.d. n.d. 0.089 ±0.002 (c) 18 h Shaking Time pH 5.2 6.4 4.9 6.7 Mn (mM) 0.0142 ±0.0001 0.0145 ±0.0003 0.1576 ±0.0006 0.155 ±0.003 Fe (mM) 7.6 ±0.2 0.135 ±0.009 n.d. n.d. Cu (mM) n.d. n.d. 1.03 ±0.02 n.d. Zn (mM) 4.42 ±0.07 1.11 ±0.03 62.8 ±0.7 5.3 ±0.1 As (mM) n.d. 0.38 ±0.01 n.d. n.d. Cd (mM) 0.0201 ±0.0003 n.d. 0.181 ±0.001 0.00095 ±0.0001 Sb (mM) n.d. 0.096 ±0.006 n.d. n.d. Pb (mM) 0.223 ±0.001 n.d. n.d. 0.103 ±0.001 an.d. = not detectable (below the limit of detection). Fe-rich replacement ore, and Zn−Pb-rich impregnation ore.9 phytoplankton primary production. These are important These chemical compositions and mineral assemblages depend potential issues related to seafloor metal-mining. on the geological setting and fluid chemistry. The chemical compositions of leachates are expected to differ among different 2. RESULTS AND DISCUSSION types of hydrothermal ores. 2.1. Release of Metals and Metalloids from Mineral Simpson et al. (2007) studied the leachability of metals and Ore Particulates. The leachates contained large amounts of metalloids from hydrothermal mineral ores collected from both Mn, Fe, Cu, Zn, As, Cd, Sb, and Pb (Table 1). The leachates active and inactive vent chimneys in the East Manus Basin from all ore samples commonly contained Zn and Mn, whereas hydrothermal field (Papua New Guinea) as part of the Solwara 8 Cd was detected from all leachates except that from the Ba-rich 1 project. They observed that large amounts of Mn, Cu, Zn, ore (HPD1313G05). The Fe−Zn−Pb-rich (HPD1313G04) and As and small amounts of Ni, Ag, Cd, and Pb were rapidly and the Zn−Pb-rich zero-age (HPD1355R04) ores released Pb. released into oxic seawater from these mineral ore samples. Only the Ba-rich ore released As and Sb. However, they did not take into account the relationship Among all leached metals and metalloids, Zn showed the between the chemical composition of the leachates and those of highest concentrations in most of the leachates produced under the hydrothermal ores. these experimental conditions. The Zn concentration was In this study, we investigated the leachability of metals and higher in the leachate from the Fe-rich ore (HPD1311G06) fi metalloids from ne particulates of various hydrothermal ores than in the leachates from the Fe−Zn−Pb-rich, Ba-rich, and collected in the Okinawa Trough. These ore samples had Zn−Pb-rich ores. ff di erent chemical compositions and mineral assemblages. As In hydrothermal ores, Zn is generally present as a well as the potential for leaching, we also determined the monosulfide mineral, sphalerite.15 Small amounts of Mn and toxicity of the leachates to a marine phytoplankton, Skeletonema Cd are present in sphalerite as impurities;16 consequently, the marinoi−dohrnii complex (formerly classified into Skeletonema amounts of Mn and Cd in the ores were positively correlated costatum,12,13 one of the ecotoxicological standard test with that of Zn (Figure S1a). As expected, the concentrations organisms used to evaluate seawater quality).7,14 On the basis of Mn and Cd in the leachates were also positively correlated of our results, we discuss the possibility of metal and metalloid with that of Zn (Figure S1b).