Vermiculite as a potential functional additive for water treatment bioreactors inhibiting toxic action of heavy metal cations upsetting the microbial balance

Abstract

A new adsorbent that combines mineral vermiculite with the yeast Saccharomyces cerevisiae, was used for Cd²⁺ removal. The influence of vermiculite presence on the toxic effects of Cd²⁺ to Saccharomyces cerevisiae yeast was evaluated as a function of the microorganisms' respiratory activity (CO₂ production). The Cd²⁺ toxicity increased with prolonged exposure time reaching the LC₅₀ value of 857 and 489 mg L^-1 after 30 and 120 min, respectively. The yeast managed to bioaccumulate 25.0 ± 0.6 mg g^-1 of Cd²⁺ at the initial Cd²⁺ concentration of 741.9 mg L^-1; the maximum Cd²⁺ adsorption capacity of vermiculite reached 25 ± 5 mg g^-1. The addition of the mineral decreased the cations toxic effect; the LC₂₀ value in vermiculite absence attained approximately 200 mg L^-1 after 30 min and decreased to 80 mg L^-1 after 2 h, while in the bio-mineral system it was at the level of 435 ± 50 mg L^-1 without a significant change in time. The mineral provided a superior living environment for the yeast by removing part of the cations, releasing essential microelements and providing a protective, clay hutch-like habitat for the cells.

Keywords: Cadmium adsorption; Clay-yeast interactions; Ecotoxicity; Saccharomyces cerevisiae; Vermiculite.