How Mushrooms Could Help Clean Up Pollution

Mycoremediation of heavy metals: processes, mechanism and affecting factors

Vinay Kumar and Shiv Kumar Dwivedi

Summarized by Anna Geldert

What data were used? In this review, researchers assessed data from over 300 previous studies on mycoremediation, a process which uses fungi to remove pollutants such as heavy metals from the environment. These studies included findings on the mycoremediation potential of 62 living species of fungi, and 21 dead species. In total, the review considered 11 types of heavy metal pollutants (mercury, cadmium, lead, chromium, copper, arsenic, manganese, nickel, cobalt, zinc and iron) as well as data on drinking water standards, and health impacts of each heavy metal from the World Health Organization (WHO).

Methods: The goal of this review was to synthesize data from existing research, and to identify which factors most affect fungi mycoremediation potential. The authors looked for trends and patterns from previous studies, and summarized findings related to the health impacts of heavy metal exposure to fungal species, as well as the biological, chemical, and physical processes that are used for the absorption of pollutants. They also identified the most important factors affecting the rate of absorption for both living fungi and dead fungal biomass. 

Results: In general, results demonstrate that both heavy metal tolerance and absorption potential differs greatly among species of fungi. Species belonging to the class ascomycete were found to tolerate higher concentrations of heavy metal pollutants, though the explanation for this is still unclear. Both living and dead fungal biomasses were able to absorb heavy metals through a variety of biological processes in the cell wall, and this absorption may be increased further through physical and chemical treatments. In regard to factors that impact absorption rate, the review found that lower pH levels, high agitation (water disturbance) rates, and low flow rates all consistently increased the absorption rate of tested fungi. Factors such as temperature, time, and heavy metal concentration varied based on the species of fungi. Lastly, this study concludes that dead fungal biomass will most likely work better than living fungi for mycoremediation, since varying pH levels, temperatures, and heavy metal concentrations are not limiting factors as dead fungal masses do not need to be kept alive.

A flow chart which starts at a light pink box titled Mycoremediation of heavy metals, which has two main paths, represented by thin black arrows. From this point of origin on the left is a gray box titled By Growing Fungi. This continues to a pink box on the left titled Genetically modified and across from it on the right is a gray box titled Non-Modified. Non-modified continues the chart on its downward path to two more boxes. The left hand box is light pink labeled Indirect Application which below it in parenthese states “By production of siderophores and secondary metabolites”. Across from the light pink box is a gray one with the label Direct Application. Both Direct and Indirect Application continue the chart downward to two light blue boxes with the titles Specific Action of a single fungus and Synergistic Action of more than one fungi, on the left and right respectively. The chart continues from these two, and again are two boxes both in an orange color. They are titled Immobilized form and Free form. Finally this side of the chart ends with two purple boxes labeled Continuous mode and Batch mode. Returning to the beginning of the chart but on the right side, is a blueish gray box titled By Fungal Biomass. This branches into a light blue box on the left titled Activation and across from it, in the same previous blueish gray color is a box labeled Direct Application. From Activation on the left the chart splits into 3 boxes. On the left is a light pink box titled Physical Activation with parentheses stating “heat, magnetic modified, etc”. In the center is a pink box titled Chemical Activation with parentheses stating “acetone, NaOH, ether, etc”. On the right is a light blue box titled Physico-chemical Activation. All 3 boxes continue the chart to a blue box titled Characterization and Application. This light blue box continues to a final box within the chart, and from the left-hand side the chart converges onto this box. This large gray box titled Factors involve in HMS Remediation process. Below it is a list that states Time, pH of the soln, Temperature, Adsorbent conc, Adsorbent dose, Aggitation rate, Medium composition, and Adsorbent type in descending order.
Fig. 1 Flowchart of mycoremediation in wastewater heavy metal treatment methods, comparing the growth of fungi and fungal biomass.

Why is this study important? This study is useful because it draws conclusions from a large body of existing work on mycoremediation, and recognizes important trends in related findings. This allows for comparisons on the mycoremediation potential of various fungal species, treatment methods, and  treatment conditions, which would be much more difficult without a cohesive summary paper such as this one. This study will enable future researchers, and engineers to create novel and efficient methods for treatment of heavy metal wastewater with fungus. 

The big picture: Pollution is one of several environmental challenges facing our planet today, with heavy metal pollutants being one of the most hazardous, due to its negative impacts on human health. Current methods for treating heavy metal contaminants in wastewater are often not economically or environmentally sustainable. Mycoremediation may provide a sustainable solution to this problem, due to fungi’s inherent ability to absorb environmental pollutants, such as heavy metals. This review provides guidance on what fungal species, treatment methods, and treatment conditions would make this remediation process most effective and efficient. 

Citation: Kumar, V., & Dwivedi, S. K. (2021). Mycoremediation of heavy metals: processes, mechanisms, and affecting factors. Environmental Science and Pollution Research, 28(9), 10375–10412.

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