The effect of heavy metals on thiocyanate biodegradation by an autotrophic microbial consortium enriched from mine tailings

Farhad Shafiei,Lukas Pajank,John W. Moreau,Mathew P. Watts

doi:10.1007/s00253-020-10983-4

Abstract

Bioremediation systems represent an environmentally sustainable approach to degrading industrially generated thiocyanate (SCN−), with low energy demand and operational costs and high efficiency and substrate specificity. However, heavy metals present in mine tailings effluent may hamper process efficiency by poisoning thiocyanate-degrading microbial consortia. Here, we experimentally tested the tolerance of an autotrophic SCN−-degrading bacterial consortium enriched from gold mine tailings for Zn, Cu, Ni, Cr, and As. All of the selected metals inhibited SCN− biodegradation to different extents, depending on concentration. At pH of 7.8 and 30 °C, complete inhibition of SCN− biodegradation by Zn, Cu, Ni, and Cr occurred at 20, 5, 10, and 6 mg L−1, respectively. Lower concentrations of these metals decreased the rate of SCN− biodegradation, with relatively long lag times. Interestingly, the microbial consortium tolerated As even at 500 mg L−1, although both the rate and extent of SCN− biodegradation were affected. Potentially, the observed As tolerance could be explained by the origin of our microbial consortium in tailings derived from As-enriched gold ore (arsenopyrite). This study highlights the importance of considering metal co-contamination in bioreactor design and operation for SCN− bioremediation at mine sites.Key points• Both the efficiency and rate of SCN−biodegradation were inhibited by heavy metals, to different degrees depending on type and concentration of metal.• The autotrophic microbial consortium was capable of tolerating high concentrations of As, potential having adapted to higher As levels derived from the tailings source.

Highlights

For higher organisms, thiocyanate (SCN−) is a known goitrogen, i.e., a chemical with deleterious anti-thyroid effects with prolonged exposure (Ermans and Bourdoux 1989); acute SCN− poisoning can occur (Gould et al 2012)
The present study aimed to evaluate the heavy metal tolerance of a previously characterized autotrophic sustainable approach to degrading industrially generated thiocyanate (SCN−)degrading consortium enriched from surface tailings of a gold mine in Western Victoria, Australia (Watts et al 2017b)
Each of the metal(loid)s tested here inhibited SCN− biodegradation to an extent and duration that depended on both type and concentration

Summary

Introduction

Thiocyanate (SCN−) is a known goitrogen, i.e., a chemical with deleterious anti-thyroid effects with prolonged exposure (Ermans and Bourdoux 1989); acute SCN− poisoning can occur (Gould et al 2012) The toxicity of this compound occurs at blood serum concentrations greater than 1 mg per 100 mL (Lage et al 1994). Gold-bearing ores naturally contain sulfide minerals that release reduced sulfur species during ore processing, which react with cyanide (CN−) to generate SCN− (Mudder et al 2001). This process can elevate SCN− concentrations to higher than 1000 mg L−1 in tailings wastewaters (Given and Meyer 1998). All cultures were incubated in triplicate simultaneously for one type of metal at a time

Methods

Results

Conclusion