Microbial Population Dynamics and the Role of Sulfate Reducing Bacteria Genes in Stabilizing Pb, Zn, and Cd in the Terrestrial Subsurface

Abstract

Milling and mining metal ores are major sources of toxic metals contamination. The Spring River and its tributaries in southeast Kansas are contaminated with Pb, Zn, and Cd because of 120 years of mining activities. Trace metal transformations and cycling in mine waste materials greatly influence their mobility and toxicity and they affect both plant productivity and human health. It has been hypothesized that under reduced conditions in sulfate-rich environments, these metals can be transformed into their sulfide forms, thus limiting mobility and toxicity. We studied biogeochemical transformations of Pb, Zn, and Cd in flooded subsurface mine waste materials, natural or treated with organic carbon (OC), and/or sulfur (S), by combining advanced microbiological and X-ray spectroscopic techniques to determine the effects of treatments on the microbial community structure and identify the dominant functional genes that are involved in the biogeochemical transformations, especially metal sulfide formation over time. Samples collected from medium-, and long-term submerged columns were used for microarray analysis via functional gene array (GeoChip 4.2). The total number of detected gene abundance decreased under long-term submergence, but major functional genes abundance was enhanced with OC-plus-S treatment. The microbial community exhibited a substantial change in structure in response to OC and S addition. Sulfate-reducing bacteria genes dsrA/B were identified as key players in metal sulfide formation via dissimilatory sulfate reduction. Uniqueness of this study is that microbial analyses presented here in detail are in agreement with molecular-scale synchrotron-based X-ray data, supporting that OC-plus-S treatment would be a promising strategy for reducing metal toxicity in mine waste materials in the subsurface environment.

The Microbiology of Metal Mine Waste: Bioremediation Applications and Implications for Planetary Health

“…The same column study described for Cd (Section 3.2.2) and Pb (Section 3.5.2) also contained Zn (23.5 g kg −1 ), initially present as silicate phases (Karna et al, 2018). After 252 days of amendment with organic carbon and sodium sulfate the column sediment comprised 31% Zn-sulfide, and far less Zn was released to the aqueous phase compared to the unamended control (Karna et al, 2016).…”

“…As well as transforming aqueous Cd, sulfate-reducing microorganisms can decrease the bioavailability of Cd in mine waste. A column study amended Cd-contaminated mine waste (67 mg kg -1 Cd) with organic carbon and sodium sulfate, and showed that the Cd was initially present as a mixture of carbonate, sulfate, nitrate and hydroxide phases, but after 252 days it comprised 39 % Cd-sulfide and 61 % Cd-carbonate (Karna et al, 2018). The sulfur-cycling genes dsrB and dsrA were significantly more abundant compared to the unamended control, and far less Cd was released to the aqueous phase (Karna et al, 2016), leading the authors to conclude that constructed wetlands are beneficial for stabilising Cd in mine waste materials.…”

“…The column study described for Cd (Section 3.2.2) where contaminated mine waste was amended with organic carbon and sodium sulfate also contained Pb (5,050 mg kg -1 ), which was initially present as a mixture of carbonate, sulfate and phosphate phases (Karna et al, 2018).…”

“…The column study described for Cd (Section 3.2.2) where contaminated mine waste was amended with organic carbon and sodium sulfate also contained Pb (5,050 mg kg −1 ), which was initially present as a mixture of carbonate, sulfate and phosphate phases (Karna et al, 2018). After 252 days amendment the waste comprised 62% Pb-sulfide and 38% Pb-carbonate, and far less Pb was released to the aqueous phase compared to the unamended control (Karna et al, 2016).…”