Study on bioaccumulation and biosorption of mercury by living marine macroalgae: Prospecting for a new remediation biotechnology applied to saline waters

Bruno Henriques, Luciana S. Rocha, Cláudia B. Lopes, Paula Figueira, Rui J.R. Monteiro, A.C. Duarte, M.A. Pardal, E. Pereira

CESAM & Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.

Abstract

This study aimed to assess and explore the bioaccumulation capabilities of three different macroalgae species, Ulva lactuca (green), Gracilaria gracilis (red) and Fucus vesiculosus (brown), very common on temperate coasts and estuaries, for the removal of mercury (Hg) from contaminated waters (with high salinity), using environmentally realistic concentrations of metal (10–100 μg L^-1). Levels of Hg accumulated by all seaweeds ranged between 20.8 and 208 μg g^-1, corresponding to bioconcentration factors of c.a. 2000. A comparative evaluation of bioaccumulation (living biomass) and biosorption (dried biomass) was performed for U. lactuca, which had displayed the best performance in accumulating Hg. The removal conducted by the living seaweed (m_macroalgae/V_solution ≈ 500 mg L^-1), although slower, was more promising since all Hg levels were reduced by about 99%, fulfilling the European criteria for drinking water quality. Pseudo-second-order and Elovich models described quite well the experimental data, assuming a process essentially of chemical nature. Determination of total Hg content in algal biomass over time, allowed to confirm and to follow the uptake of this metal by the living organism. Volatilization of Hg or its conversion to organo-metallic forms (0.02–0.05%) was negligible during the decontamination process.

Overall, the results are a contribution for the development of an efficient and cost-effective water remediation biotechnology, based on the use of living macroalgae to promote the removal of Hg.

Graphical abstract

Keywords: Mercury; Organo-metallic forms; Marine macroalgae; Biosorption; Bioaccumulation; Kinetic modeling.