Literature Review Blog II

Title: Effects of temperature warming during a bioremediation study of natural and nutrient-amended hydrocarbon-contaminated sub-Antarctic soils

1. What is the study’s objective/hypothesis/question?

The study looked into the use of in-situ bioremediation using microorganisms to degrade petroleum contaminated soils at sub-Arctic conditions, including soils, temperature and vegetation. Temperature was the most important variable, in that the hydrocarbon mineralization rate was assessed on artificially contaminated soils that mimicked Arctic conditions.

2. What is the rationale and relevance of the question? (i.e. why was the study done?) 

The Arctic is recognized as the last pristine zone, "almost uncontaminated by anthroprogenic hydrocarbons". However, due to petroleum contamination, identified as the most significant, both coastal marine and terrestrial areas are becoming polluted. Bioremediation, for now, is the only cost effective and plausible technique feasible in Antarctica's environment and the large scale area of the region. This study was conducted due to the assumption that sub-Arctic air and soil temperatures have been thought to be too low for effective bioremediation. However, the metabolism of cold-adapted organisms is prepared to function well at low temperatures and such organisms have been useful in similar processes in Alpine, Arctic and Antarctic areas.

3. What is the relevance of this topic/question to engineering? (i.e. is it urgent or essential reading for a civil/environmental engineer?)


This topic is essential to engineering due to society's intrinsic dependence on petroleum, with no migration away from such in the foreseeable future. Since this habit will continue, we are bound to encounter pollution issues and likewise the clean ups of these spills. As it is indisputable that we cannot just destroy a single environment and walk away unscathed, we must then find a way to clean up our messes. Particularly concerning environmental engineers that work with a lot of microorganisms and understand the fragility of such, this presents a whole new area of study between the relationship between different microorganisms and their behaviors impacted by the temperature. Since little is known about these dealings, it is essential we study and learn quickly before we make a mess too big to sweep under the rug.

Figure 1. Map of experimental location and diagrams of tested soil plots.

4. What methodological approach (design, analysis, etc.) has been used? (i.e. what was done?)

The experiment was conducted in Kerguelen Archipelago, off the coast of Antarctica but also in the middle of no where. In an area with no known history of hydrocarbon contamination, two pristine soils were selected. The first one was beneath a healthy vegetal cover, while the second one was from a dry desert region. Five enclosures were set up in each soil type and each enclosure was contaminated with about 500 mL of diesel fuel or Arabian light crude oil and half were covered with a black plastic sheet. Half were then treated with 100 mL of the slow release fertilizer Inipol EAP-22. All of the plots were sampled regularly for total, heterotrophic and hydrocarbon-degrading bacteria and temperature readings.

5. What were the results of the study? (i.e. what did the investigators find?)

    The measured temperatures ranged from 0*C in winter to more than 20*C in summer in both soils. As expected, temperatures were always warmer in covered soils than in similar uncovered soils. Total bacterial counts did not differ significantly between pristine and contaminated zones (2*10^8-6*10^8). In both soils, the heterotrophic bacterial abundance increased more than one abundance after 5 months of pollution. For both contaminates, fertilizer addition had no clear benefit nor drawback on heterotrphic bacterial counts in vegetated soil, but a slight positive effect on corresponding desert soil plots. After 2 years, soil coverage had a significant (more than one order of magnitude) effect on vegetated soil, but no clear effects on desert soil.
    Before contamination, the hydrocarbon degrading bacteria was never more than 0.5% of the total bacterial count. After contamination, a "spectacular enrichment" in such bacteria occurred in every plot, sometimes exceeding 80% of the total population after 1 year of contamination. However, these numbers began to decrease in the second year of contamination. Numbers were generally higher in the covered soils than in the uncovered ones.

6. What were the strengths & weaknesses of this study? Are the results valid? (i.e. its study design, appropriateness of the method(s), relevant study group, sufficient sample size, appropriate study conduct, data gathering, subject follow-up, influences of bias, method of analysis, discussion, currentness and comprehensiveness of the listed references) 

One strength of this study was its decision to test multiple plots of land deemed 'pristine' in two different conditions, strong vegetation and desert. This increased the possibility for a real life situation, as we can't really choose to have a crisis in one condition if we know more about it. It gives us more flexibility with which to tackle the pollution problem. One weakness of this study is its 2 year test period. While it was a good idea to have the experiment go on for so long, a lot of times we do not know the whole impact of something, as a contaminant leak, until decades later. 2 years demonstrates just a fraction of the scenarios that may unfold in the impending sites. There was a comprehensive methodology, a strong conclusion and plenty of references to support this study.

7. Do the conclusions follow logically from the design and results? 

The conclusions definitely follow logically from the design and the results, as under normal temperature conditions, this microorganisms would thrive. However, in this study, it was not known if such survival could continue under these temperature conditions. To me, the study is well designed, well performed and well analyzed. It seems like a really neat field to be in for job potential as we are realizing how destructive/messy we are as humans.

8. How do the results relate to current practice and how might they influence future practice? (i.e. what does the answer mean anyway? So what and who cares?) 

The results relate to current practice as we now know for certain that this microorganisms can grow and perhaps even thrive in sub-Arctic temperatures. Before it was not known if this even a possibility. For future practice, more studies do need to be done for the different types of pollution, as this one was strictly oil in hopes of mimicking a spill. If different situations can be replicated, then perhaps more studies can be done on the different qualities and attributes of these bioremediation microorganisms to address different pollution scenarios. The report even states itself "care must be taken in extrapolating the results of any experimental study to more environmental conditions".

References 

Delille, D., Coulon, F., & Pelletier, E. (2004). Effects of temperature warming during a bioremediation study of natural and nutrient-amended hydrocarbon-contaminated sub-Antarctic soils. Cold Regions Science and Technology, 40(1), 61-70.