Abstract
Portmán Bay is a heavily contaminated area resulting from decades of metal mine tailings disposal, and is considered a suitable shallow-water analogue to investigate the potential ecotoxicological impact of deep-sea mining. Resuspension plumes were artificially created by removing the top layer of the mine tailings deposit by bottom trawling. Mussels were deployed at three sites: i) off the mine tailings deposit area; ii) on the mine tailings deposit beyond the influence from the resuspension plumes; iii) under the influence of the artificially generated resuspension plumes. Surface sediment samples were collected at the same sites for metal analysis and ecotoxicity assessment. Metal concentrations and a battery of biomarkers (oxidative stress, metal exposure, biotransformation and oxidative damage) were measured in different mussel tissues. The environmental hazard posed by the resuspension plumes was investigated by a quantitative weight of evidence (WOE) model that integrated all the data. The resuspension of sediments loaded with metal mine tails demonstrated that chemical contaminants were released by trawling subsequently inducing ecotoxicological impact in mussels’ health. Considering as sediment quality guidelines (SQGs) those indicated in Spanish action level B for the disposal of dredged material at sea, the WOE model indicates that the hazard is slight off the mine tailings deposit, moderate on the mine tailings deposit without the influence from the resuspension plumes, and major under the influence of the resuspension plumes. Portmán Bay mine tailings deposit is a by-product of sulphide mining, and despite differences in environmental setting, it can reflect the potential ecotoxic effects to marine fauna from the impact of resuspension of plumes created by deep-sea mining of polymetallic sulphides. A similar approach as in this study could be applied in other areas affected by sediment resuspension and for testing future deep-sea mining sites in order to assess the associated environmental hazards.
Highlights
Portmán Bay is a heavily impacted area resulting from decades of metal mine tailings disposal that lasted until 1990
The resuspension experiment of these sediments demonstrated that chemical contaminants are released from the sediments inducing ecotoxicological impact in mussels moored 3 meters above the seafloor
The integrated approach used in this study is useful to detect and quantify the environmental hazard posed by a mine tailings deposit, especially in case of sediment resuspension
Summary
Portmán Bay is a heavily impacted area resulting from decades of metal mine tailings disposal that lasted until 1990. The assessment of the impact of contaminated marine areas, such as mine tailings deposits should be investigated in different environmental matrices (sediment, water and biota) combining information from the chemistry and ecotoxicological impact, integrating data from bioavailability, bioaccumulation and biomarker responses and from ecotoxicological bioassays on bioindicator species (Viarengo et al 2007). The quantitative weight of evidence (WOE) model (Sediqualsoft), is considered to be a promising tool to assess the environmental hazards and ecological risks since it integrates data from the sediment chemistry, bioaccumulation, biomarkers responses and toxicity bioassays (Piva et al.2011, Benedetti et al 2012, 2014, Regoli et al 2014, Bebianno et al 2015)
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