One of the most pressing challenges humanity is facing today is environmental pollution with difficult to degrade chemical compounds resulting from human industrial and agricultural activities. These pollutants, which include poly-aromatic hydrocarbons, pesticides, polychlorinated compounds, and heavy metals, persist in the environment for decades, causing havoc in natural habitats and posing a severe threat to the health of living organisms, including humans.
The persistence of these hydrocarbons depends on a variety of factors, including their chemical structure, bioavailability, concentration, climate, pH, oxygen content, and soil type. Among these, the length of the hydrocarbon chains plays a pivotal role. Long-chain exhibit increased hydrophobicity and affinity for binding to the soil’s mineral and organic components. This reduces their bioavailability and thus ability to be degraded, allowing them to stay in the soil for extended periods. While some of these organic compounds can be degraded through abiotic processes like photo-oxidation or chemical oxidation, degradation through bioremediation stands out as the optimal method for hydrocarbon removal.
Bioremediation, a process that takes advantage of living organisms’ abilities to remove or transform pollutants into less persistent forms, is one of the most anticipated new methods in the battle against pollution. Here communities of bacteria, fungi (mycoremediation) and plants (phytoremediation) step in, working together to break down hydrocarbons into more manageable compounds. However, implementing these bioremediation techniques in the real world is no easy task, as the lack of standardized protocols for biological decontamination methods has led to varying results in published studies. To tackle this , a recent study has set out to explore the effectiveness of treatments with bacterial, fungi and plants individually and in combination. The primary goal of the study was to unlock and characterize the potential of organisms in combating aged heavy fuel oil spills and offer a ray of hope in the struggle for a cleaner, greener future.
Using soil sources from an abandoned industrial area in Spain, the researchers performed a multitude of chemical analyses to characterize the qualities of the soil. These included soil pH, water holding capacity, soil texture, ion concentrations, total petroleum hydrocarbons (TPH) and more, all according to the standards outlined by the World Reference Base for Soil Resources. What they found was a soil with traits that could provide biological support to organisms, but was fine in texture, which can cause a decrease in the ability to retain water and good aeration. Using this assessment, a legume found growing on-site already, alfalfa (Medicago sativa L.), the white-rot fungi oyster mushrooms (Pleurotus ostreatus) and a culture of hydrocarbon-degrading bacteria isolated from polluted soil in question were all tested individually and in combinations of bacteria-fungi, plant-fungi and bacteria-plant-fungi to evaluate their effect on the degradation of aliphatic and aromatic long-chain hydrocarbons.
Compared to the control pots of soil left to degrade by natural treatment (NT), the researchers found that the tested treatments to be up to 20 times more effective in the complete and/or partial degradation of TPH. The treatments involving fungi were best at removing aliphatic hydrocarbons, while the plant treatment and the bacteria-plant-fungi treatment were the only ones to show significant reduction of aromatic hydrocarbons. The overall winner was clearly the comprehensive treatment involving all three organisms with aliphatic, aromatic and total hydrocarbon chains degrading by respective percentages of 48%, 35% and 41%. However, the researchers note that median percentages were used as the complexity of the various intermediate hydrocarbon fractions and confounding environmental exposures could have caused some of the issues they faced in data variability.
The future of environmental cleanup, as glimpsed through this research, beckons with promise. Yet, as with any scientific endeavour, challenges remain. The researchers acknowledge the complexities of identifying and employing efficient pollutant-degrading organisms under real-world conditions, and have provided in their study a path for using organisms from on-site to ease the selection process. Consequently, this realization highlights the need for further research and the development of standardized protocols for bioremediation techniques.
In closing, as it becomes more and more clear that the battle against environmental contamination is far from over, there is hope in research exploring the possibilities of bioremediation, there’s reason to believe that we stand on the threshold of a more sustainable future.
Cover photo by Patrick Hendry on Unsplash
Gallery photos by Adrian Lange (1), Rob (2), and Zoe Schaeffer (3) all on Unsplash
Journal Article: Guirado M, García-Delgado C, Pindado O, et al. Bioremediation study of a hydrocarbon-contaminated soil by profiling aromatic and aliphatic chains. Applied Soil Ecology. 2023 June 1;190. doi: https://doi.org/10.1016/j.apsoil.2023.104983
