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DEEP SEA MINING AND ITS POSSIBLE IMPACT ON SURFACE PHYTOPLANKTON AT HYDROTHERMAL FIELDS

There is growing awareness of the potential for mining of seafloor massive sulfide (SMS) deposits. Most of these metals are present as insoluble minerals on the seabed; however, they may become oxidized and be transformed to labile forms after mechanical crushing during their extraction. While mining operations will be well-designed to minimize marine environmental impacts, risks of accidental leakages of metal-contaminated seawaters to ecosystem will remain. We conducted metal leaching tests from powdered SMS ores (black-, pyrite massive-, and barite ore) which were collected at hydrothermal fields in the Okinawa Trough, Japan. Released metal amounts roughly correlated with their solid phase concentrations; however, Cu and Cd amounts released from the pyrite ore were higher than might have been expected. Incubation experiments with eight phytoplankton species indicated that the pyrite ore eluate was the most toxic and all species ceased to grow when the eluate concentration exceeded 1%; at this level, the Cu and Cd concentrations were ca. 0.6 and 0.15 ppm, respectively. While the Pb levels were higher, and the Cu and Cd levels were lower, in the eluate from the black ore than in the pyrite eluate, the black ore eluate was less toxic for all species than the pyrite eluate overall. Our result suggests that crushed and oxidized SMS ores produced during mining would release easily toxic metals to seawater. More quantitative assessments for metal leaching characteristics and their toxicities would be required to discuss suitable impact mitigation strategies.

Authors

Koshikawa, H., Natl. Inst. for Environ. Studies, Japan, koshikaw@nies.go.jp

Fuchida, S., Natl. Inst. for Environ. Studies, Japan, fuchida.shigeshi@nies.go.jp

Yokoyama, A., Natl. Inst. for Environ. Studies, Japan, yokoyama.akiko@nies.go.jp

Tsuboi, S., Natl. Inst. for Environ. Studies, Japan, tsuboi.shun@nies.go.jp

Yamagishi, T., Natl. Inst. for Environ. Studies, Japan, yamagishi.takahiro@nies.go.jp

Kawachi, M., Natl. Inst. for Environ. Studies, Japan, kawachi.masanobu@nies.go.jp

Details

Poster presentation

Session #:082
Date: 02/28/2017
Time: 15:30 - 16:30
Location: Poster/Exhibit Hall

Presentation is given by student: No

PosterID: 602