Good Things Come in Small Packages: Literature Review on Mycoremediation
Jessica HoffmanMushrooms: most believe they are insignificant forest growth and a minor food source in people’s diets. However, these small organisms have massive potential bundled up in their networks of roots. A mushroom’s roots, or mycelia, carry out natural processes capable of environmental remediation. Mycelia are composed of a mass of thread-like structures called hyphae. The hyphae form dense, far reaching networks underground that absorb nutrients in the soil by secreting enzymes. Their enzymatic and absorption abilities make fungi a great candidate for several methods of remediation, or mycoremediation, the term used to describe the process of fungi acquiring and degrading pollutants in the environment through their mycelia. Because mycoremediation wears many hats, mycelia can be used as biological filters, sponges for toxins, and strengtheners of soil.
The filtration aspect of mycelia, or mycofiltration, has been widely studied as a method to purify storm water. In one study, the fungal species S. rugoso-annulata proved to remove up to 20% of E. coli particles from storm water (Taylor). E. Coli bacteria are typically harmless but some strains have been known to cause illness. Besides being a possible cause of illness, E. coli is considered an indicator for fecal contamination in water. The removal of these bacteria is pertinent to communities everywhere as all humans need sanitary water. The study set up samples to pour contaminated storm water through the natural filter. The fungus was added to two different substrates. Three containers enclosed alder wood chips- one without the fungus, one with the fungus, and one with the fungus after “vigorous testing” (fungus put through several extreme temperature changes). Two containers enclosed a mix of 75% alder chips and 25% rice straw- one without the fungus, and one with non-vigorously tested fungus. These samples were replicated three times for a total of fifteen containers. The storm water was allowed to pass through the filters and samples were collected after different time intervals. The greatest success was a 20% decrease in E. coli concentration in the samples with non-vigorously tested fungus on 100% wood chips. The results were statistically significant when compared to the control. These results also suggest from the success of the vigorously tested fungus that in harsh conditions, S. rugoso-annulata mycelium can remove E. coli (Taylor). This suggests the resistant nature of fungi and its ability to remediate in harsh conditions.
Further proving the resistance of fungi, a study concluded the ability of Irpex lacteus and Pleurotus ostreatus species to remove polycyclic aromatic hydrocarbons (PAHs) from soil (Bhatt). PAHs are carcinogenic toxins emitted from industry. PAHs are of great health concern; they can cause skin and immune system damage as well as promote tumor production. These pollutants are difficult to cleanup; they stay in the environment for a long time and do not break down in water (Nordholm). Therefore, mycelia offer an efficient, green method for the removal of these harmful chemicals. This study focused on two species of fungi, Irpex lacteus and Pleurotus ostreatus, and two types of soils, an area with a former tar-producing plant (A) and a preserved wooded area without the tar-producing plant (B). The soils were placed between two layers of mycelium on straw. There were six samples of each soil/fungus combination and results were measured after 14 weeks of growth. For soil A, Irpex lacteus had significantly removed more PAHs from the soil than Pleurotis ostreatus. Soil B showed similar results for both species. As expected, Soil A’s fungi removed more PAHs than Soil B (Bhatt). PAHs are found in tar deposits so soil A had more PAHs available for removal. These species exhibited biodegradation abilities in which fungi secrete enzymes through their hyphae to break down pollutants and toxins (Kulshreshtha).
In comparison, both studies delved into the biodegradation abilities and resistance of fungi. Also, both studies produced significant results of pollutant removal when compared to a control. Clearly, more trials and samples would bolster up the results and conclusions of both trials. However, there are some differing strengths and weaknesses when comparing the results. The study on PAH removal allowed for adequate maturation of the mycelia, whereas the study about E. coli mycofiltration did not. The extended period of growth (14 weeks) in the PAH study fortified the results and added stability to the experiment. The E. coli study was subjected to weakened, less accurate results due to immature, unstable mycelia cultures. On the other hand, the E. coli study showed strength as it was more up-to-date than the PAH study. The E. coli study, completed this year, used more current strategies and technology than the PAH study, produced in 2002. The PAH study’s results may be out of date in the world of science where knowledge is rectified and rapidly expanded every minute.
In addition to removing carcinogens, studies have been conducted and have concluded that fungi are able to break down crude oil. In one study, the effects of an ecologically engineered system (EES) on an oil-contaminated river were measured. The research took place at a river in Fishersville Mill. This river is contaminated by thousands of gallons of Bunker C crude oil. The EES was comprised of three successive “filters” composed of four anaerobic microbial species, four mycelium species, and five plant species. While the results are less conclusive with the inclusion of other filtering organisms, there is evidence to suggest that mycelia have crude oil degrading abilities. In the study, the concentrations of petroleum hydrocarbons (PAHs and aliphatic hydrocarbons) were measured after EES treatment using mass spectrometry. In mass spectrometry, a sample is bombarded with electrons, breaking the molecules into charged ions. The ions are separated by mass, which is used to identify and determine the concentration of the molecule. The contaminated water was passed through the bacteria filter, then the mycelia filter, and then the plant filter. The water was sampled at the different stages periodically for five months. For aliphatic hydrocarbons, fungi reduced concentration after bacteria filtration by 5.2%. The entire system reduced aliphatic hydrocarbon concentration on average by 95.2% from the baseline. For PAHs, fungi reduced concentration after bacteria filtration by 67.1%. The EES reduced PAH concentration on average by 91% from the baseline. Both average reductions in PAH and aliphatic hydrocarbon concentrations were thrown off by the plant filter treatment which actually increased hydrocarbon concentrations by 22.4% and 58.4% respectively. This increase may have been caused by evaporation that decreased water volume thus increasing concentrations of pollutants relative to the amount of water (Schenker). Overall, the results suggested a significant decrease in contaminants when compared to the control of unfiltered water. This article demonstrates the effect of using fungi in tandem with other bioremediating organisms. The combining efforts of bioremediating organisms can produce widely applicable results for many environments if more research is conducted.
Not only are fungi ample filterers and absorbers, they are also sufficient soil retainers. Soil quality can be improved with the introduction of fungi to an area. A study was conducted on the tensile strength (maximum amount of stress that can be withstood) and abrasion resistance (ability to resist erosion) of soil with and without different species of mycelia. The study tested species of fungi on sandy clay loam with and without glucose. Six species and a control without fungus were tested for each treatment. The species of fungi produced significant differences in soil stability and strength when compared to the control. Also, the loam with glucose had higher resistance and strength than the plain loam with the same species of fungi as the glucose served as energy and source of growth for the mycelia. The hyphae of the fungi species formed different shapes and holds on soil particles but the general results remained the same. The results suggest that the stability of the soil was directly related to the strength of the soil. The hyphae were able to hold onto soil particles and increase the tensile strength. The mycelia’s grip on soil withstood more weathering and wind erosion than plain soil (Tisdall). As always, the experiment should be repeated for confirmation. However, this research applies to the entire globe: unhealthy soil matched with wind erosion spreads pollutants and does not efficiently sequester carbon. Healthy soil is able to absorb more carbon, reducing the greenhouse effect problem.
One may be thinking: Humanity has found its panacea! Not quite. While there are proven remediation abilities in mycelium, further study is needed. Research is limited to a recent surge in interest in remediating properties of fungi. More results will have to be conducted before programs for mycoremediation are put into place. One significant problem proposed in an article is the disposal of toxic mycelia. It has not been entirely proven that fungi can successfully exhibit bioconversion by detoxifying absorbed pollutants. This brings about the problem of safe disposal of the now toxic mycelia (Kulshreshtha). Even more, it has been suggested that some species of fungi produce ozone depletors when carrying out mycofiltration. One article displayed the species that produced dangerous N2O gas (Daniels). However, as mentioned before, further research is needed.
Works Cited
Bhatt, M. Mycoremediation of PAH-contaminated soil. Folia microbiologica 47.3 01 Jan 2002: 255-258. Academia Scientiarum Bohemoslovaca.. 09 Sep 2014.
Daniels, Russell James. Nitrous Oxide Emissions of Higher Fungal Mycelium Under various Wastewater Concentrations. Order No. 1534032 State University of New York College of Environmental Science and Forestry, 2012 Ann ArborProQuest. 7 Sep. 2014 .
Kulshreshtha, Shweta. Mushroom as a product and their role in mycoremediation. AMB Express 4.1 2014: 1-7. Springer. 07 Sep 2014.
Nordholm, Lars. “Polycyclic Aromatic Hydrocarbons in Smokehouses.” Scandinavian Journal of Work Environment & Health.Vol. 12, No. 6 (1986): 614-18. Polycyclic Aromatic Hydrocarbons (PAHs). EPA, 2008. Web. 16 Sept. 2014.
Schenker, Jakob. Ecological Remediation using Bacterial, Fungal, and Plant Microcosms: An Effective Solution for Bunker C Crude Oil Contamination in Waterways. Order No. 1561314 The University of Vermont and State Agricultural College, 2014 Ann ArborProQuest. 23 Sep. 2014
Taylor, Alex. Removal of Escherichia coli from synthetic stormwater using mycofiltration. Ecological engineering 2014: null. Elsevier. 07 Sep 2014.
Tisdall, Judith M. Stabilisation of soil against wind erosion by six saprotrophic fungi. Soil biology & biochemistry 50 01 Jul 2012: 134-141. Elsevier. 07 Sep 2014.