Natural community of macroalgae from chromium-contaminated site for effective remediation of Cr(VI)-containing leachates.

The natural macroalgal community, which developed in the unique and extremely Cr(VI)-polluted aquatic reservoir situated near a historical chromium-waste landfill, was studied in order to recognize the main mechanisms of Cr(VI) detoxification by the algal species. The conducted taxonomic analysis revealed mixed composition of the filamentous forms of algae and showed that three species of Tribonema, namely T. vulgare, T. microchloron and T. viride, which have not been studied before with regard to the mechanisms of Cr(VI) removal, are likely responsible for the effective bioremediation of this highly Cr(VI)-polluted habitat. The studied algal community, with the ability to grow in extremely high concentrations of Cr(VI), i.e. up to ca. 6150 times the upper limit for surface water, exhibited hyperaccumulative properties for chromium (max 16230 mg/kg dry weight) under the given environmental conditions. We found that the main mechanism of Cr(VI) detoxification was reduction followed by Cr(III) biosorption - feasibly by ion exchange and complexation mechanisms - and that the excellent efficiency of chromium reduction under the given, unfavorable weakly alkaline conditions indicates the biological origin of this process. It was concluded that the examined reservoir inhabited by the algal community can be used, after some modifications, as a simple cost-effective "bioreactor" allowing the reduction of chromium concentration to the desired level. Moreover, the conducted studies are also essential to obtain in-depth knowledge and should also be helpful in the relevance of the community for its further application as a potential biosorbent of Cr(VI) on a global scale.