In the previous series of blogs, the various sources of mercury and radionuclide pollution in water had been covered. The identification of problems often requires solutions to address them and in recent years, nature-based solutions (NBS) to environmental problems have gained prominence. Bioremediation falls under the umbrella of NBS and utilises a range of microorganisms or plants to detoxify environments (Gouma et al., 2014). This blog will attempt to consider possible bioremediation strategies to tackle mercury and radionuclide pollution.

 

Mercury

An identified method for mercury bioremediation is through mercury resistant bacteria, which contain a set of genes known as mer. These mer genes contain different proteins which can reduce ionic mercury such as Hg+2, which can form methylmercury, into its less-toxic elemental form Hg0 (Dash & Das, 2012). However, there are disadvantages to this method as elemental mercury can still be oxidised into Hg+2 through sunlight (photochemistry) and interactions with other oxidising agents (Ruiz et al., 2011). While the bacteria Enterobacter cloacae is resistant to methylmercury, this bacteria is unable to remediate methylmercury. It instead produces a bioluminescent response, hence playing a potential role as a methylmercury bioreporter (Din et al., 2019).

 

Radionuclides

Similarly, the bio-reducing capabilities of microorganisms have the potential to remediate radionuclides. Prokaryotes are able to reduce dissolved oxidised radionuclides to an insoluble precipitate, facilitating the ease of removal (Singh et al., 2023). An example would be the 1990s bioremediation of Vromos Bay in Bulgaria which was contaminated by the uranium, radium and thorium from mine tailings (Groudev et al., 2001). The bioremediation process involved sulphate reducing bacterium T. thioparus and T. neapolitanus, which had successfully precipitated soluble uranium and absorbed radium into the solid organic substrates in the cell (Groudev et al., 2001).

 

Overall, the removal of toxic substances through microbial bioremediation is promising and have been heavily researched. However, these methods are rarely used due to complications where the responses of other additional pollutants have to be considered and the process of bioremediation may take a long time to treat polluted environments (Vinyaka & Kadol, 2022). Despite this, the advancement of future technologies may be able to harness microbial bioremediation’s potential.

 

References:

Dash, H. R., & Das, S. (2012). Bioremediation of mercury and the importance of bacterial mer genes. International Biodeterioration & Biodegradation, 75, 207–213.

Din, G., Hasan, F., Conway, M., Denney, B., Ripp, S., & Shah, A. A. (2019). Engineering a bioluminescent bioreporter from an environmentally sourced mercury‐resistant Enterobacter cloacae strain for the detection of bioavailable mercury. Journal of Applied Microbiology, 127(4), 1125–1134.

Groudev, S. N., Georgiev, P. S., Spasova, I. I., & Komnitsas, K. (2001). Bioremediation of a soil contaminated with radioactive elements. Hydrometallurgy, 59(2), 311–318.

Gouma, S., Fragoeiro, S., Bastos, A. C., & Magan, N. (2014). Bacterial and fungal bioremediation strategies. Microbial Biodegradation and Bioremediation, 301–323. https://doi.org/10.1016/b978-0-12-800021-2.00013-3

Ruiz, O. N., Alvarez, D., Gonzalez-Ruiz, G., & Torres, C. (2011). Characterization of mercury bioremediation by transgenic bacteria expressing metallothionein and polyphosphate kinase. BMC Biotechnology, 11(1), 82–82.

Singh, G., Bhadange, S., Bhawna, F., Shewale, P., Dahiya, R., Aggarwal, A., Manju, F., & Arya, S. K. (2023). Phytoremediation of radioactive elements, possibilities and challenges: special focus on agricultural aspects. International Journal of Phytoremediation, 25(1), 1–8.

Vinayaka, K. S., & Kadkol, S. (2022). Advances in bioremediation of organometallic pollutants. Biological Approaches to Controlling Pollutants, 233–239. https://doi.org/10.1016/b978-0-12-824316-9.00012-4