Leaching of Metals and Metalloids from Hydrothermal Ore Particulates and Their Effects on Marine Phytoplankton

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.

Differential heavy metal sensitivity in seven algal species from the NIES culture collection based on delayed fluorescence assays

“…Recent studies of various hydrothermal ores collected from the middle Okinawa Trough have shown that metal and metalloid compositions of the leachates do not completely reflect the internal chemical compositions and mineral assemblages of the ores (Fuchida et al . ). This suggests that it is difficult to predict the risk of toxic effects during mining operations in advance.…”

“…We determined the ecotoxicological impact of three transition metals, zinc (Zn), lead (Pb), and copper (Cu), based on a previous study showing that these metals are relatively leachable from hydrothermal ores (Fuchida et al . ). We also evaluated the impact of those metals on algal community structure by flow cytometry (FCM) in a co‐culture experiment.…”

Geological, Mineralogical and Textural Impacts on the Distribution of Environmentally Toxic Trace Elements in Seafloor Massive Sulfide Occurrences

“…During this process, fine sulfide particulates are created and may also undergo geochemical changes including partial dissolution and oxidation. If any leaching of metals produced during dissolution is not balanced by their precipitation (as oxide/oxy-hydroxide/chloride) or adsorption onto oxides, there is the potential for local accumulation of dissolved metals into the water column as shown in leaching experiments not only by the scientific community but also those taken as a regulatory need for environmental risk assessments [4][5][6][7][8][9]. All studies demonstrate a release of metals and highlight Cu, Zn, Pb and Cd as having the highest dissolved concentrations, which they largely attribute to galvanic coupling [4,5,9].…”

“…Of particular interest is a study of submarine tailings deposition from a Pb-Zn mine in Greenland by Josefson et al (2008) [56] that provided a threshold response of benthic macrofauna for Pb of 200 mg/kg. Moreover, in the context of accidental leakage and dispersion of sulfides during mining, the shallow marine environment also has the potential to be impacted and, based on a recent study by Fuchida et al (2017) [5], has the strong potential to be toxic for marine phytoplankton with Pb, Cu and As highlighted as significant toxicants. This is in agreement with other studies, where phytoplankton in particular is very sensitive to As (3 µg/L), suggested to be a result of its range of oxidation states and subsequent bioavailability [61,62].…”

Identifying Toxic Impacts of Metals Potentially Released during Deep-Sea Mining—A Synthesis of the Challenges to Quantifying Risk

“…Already studies have demonstrated that metals can exert a toxic effect to marine phyto-and zooplankton species (e.g., Hirota, 1981;Hu, 1981;Moraitouapostolopoulou and Verriopoulos, 1982;Caroppo et al, 2006;Fuchida et al, 2017) and can lead to metal accumulation (bioaccumulation) in higher trophic levels of food chains (Amiard Triquet et al, 1993).…”