I am taking an Academic English class called Scientific Reports Writing. I have to write two papers in this class on a specific scientific subject. I decided to post my work online so that everyone can read it. If you have to take Science 311 at University of Calgary, this paper even give you an idea on what to expect.
by
Sanuja Senanayake
Dr. S1234567
Science 311
28-February-2012
[Word Count: 1244]
Introduction
Petroleum hydrocarbons (PHC) are complex natural compounds often found in subsurface reservoirs. The extracted hydrocarbons in chemicals from reservoirs are refined to produce valuable petroleum products. The complex nature of hydrocarbons are important to prevent natural degradation of economically important reservoirs (Aitken et al. 2004). However, on the surface soil it is important to promote degradation to prevent or minimize the environmental damage from oil spills. Furthermore, the effects of cyclic changes in anaerobic elements, specifically temperature changes, effects the biodegradation process of petroleum-contaminated top soil layers. (Chang et al. 2011a) Soil contamination has occurred already at Canadian Forces radar base in the Arctic region, where diesel fuel has leaked into the soil over the last few decades. In the Arctic, studies have found that the rate of biodegradation of total PHC varies with freeze-thaw conditions (Chang et al. 2011a), which fluctuate temperature, resulting in variations in nutrition levels of the soil. Recent studies indicate the success of an alternative method of bioremediation, the use of microorganisms to remove contamination. In particular, this paper will address the use of isolated low-temperature adapted microorganisms as an effective artificial process to clean up soil contamination.
Biodegradation Depends on the Survival of Organisms in Soil
While it is beneficial to hinder biological activities under freezing conditions such as freezing food to prevent it from rotting, facilitation of biodegradation of PHC in the sub-arctic using artificial means depend on the survival of organisms under low temperature freeze-thaw conditions (Walker et al. 2006). Out of millions of microorganisms found in soil samples, only very few bacteria can survive these sub-arctic conditions. Until the last decade, few significant studies were performed on this subject. In 2006, soil samples were collected from Calgary, Alberta (Walker et al. 2006). The samples were placed in a closed system cryocycler, a device that uses liquid baths at different temperatures to heat up and cool down an experimental system, consisting of two ethylene glycol circulating baths, one at -18 oC and the other at 5 oC, to generate cyclic freeze-thaw conditions. Using cryocycler, it was discovered that most cultures did not survive the 48 free-thaw cycles, and the overall biological population decreased by 30,000 times during the experiment. However samples containing Chryseobacterium sp. strain 14 possessed antifreeze properties. These beneficial properties prevented ice recrystallization(IR) in the soil, allowing biological activities to be sustained under low temperatures. This organism had also been found in Antarctic glaciers (Christner et al. 2003). Walker and his team (2006) used these samples to theorize that these unique adaptations to freezing conditions may have been triggered by the sudden increase in temperature due to Chinook winds in Calgary. Even though exactly the same temperature conditions are not observed in the high Arctic, using these isolated bacteria with IR properties in high concentrations with fertilisers could allow bioremediation to treat PHC-contaminated sites in the Northern regions.
Effects of Temperature Change on Biodegradation
In situ biodegradation is an effective method to combat PHC contaminated soil in the Arctic region. Chang and co-researchers (Chang et al. 2011a) collected several documented petroleum-contaminated soil samples from isolated sub-Arctic military sites. Contamination had occurred in these samples as a result of oil spills between 1954 and 1974. The samples were placed in stainless steel tanks that controlled pressure, temperature, moisture and soil nutrient levels to mimic environmental conditions from historical data collected by Environment Canada. The temperatures were changed from -5 to 14 oC to reproduce the freeze-thaw seasonal conditions over a period of 160 days. Micro-organisms respiration process generates CO2 and decreases the O2 in the environment (Chang et al. 2011a). Therefore metabolic activities of micro-organisms were observed based on levels of O2 and CO2 in the samples. Biodegradation activity significantly increased with the rapid increase of the temperature from 4 to 14 oC, proving that higher temperatures in the thaw cycle are the main drive behind biodegradation of hydrocarbons in arctic soil. Further observations were made by Chang and another group of scientists (Chang et al. 2011b), from which they found that constant temperature hinders petroleum hydrocarbons biodegradation (Chang et al., 2011b). Petroleum-contaminated soil from the same period and the same area was studied with respect to total petroleum hydrocarbon levels. In some samples, soil nutrient levels were amended by providing the right temperature and nutrients for bacteria growth. The temperature of these samples was increased from 1 to 10 oC at a rapid pace. The study found that this temperature change, over a two-month period, had significantly increased the biodegradation of petroleum hydrocarbons, as opposed to constant temperature conditions. When the temperature was increased from 1 to 6 oC, and 6 to 10 oC, the researchers found that the O2 and CO2 levels reflected higher microbial respiration activities in the soil. Samples under constant temperature seems to hindered the degradation (Chang et al. 2011b) process when it compared against the samples subjected to freeze-thaw cycles. Since low temperature conditions either slow down or hinder biological activities in soil completely, it may be possible to develop mechanisms to change the temperature of the soil in order to revive the microorganisms to promote natural biodegradation of PHC in the Arctic.
Bioremediation is a Viable Option for PHC Decontamination
A crucial element for the successful bioremediation depends on specific organisms that can survive the temperature conditions of the sub-arctic (Ferguson et al. 2008). Ferguson and his team of scientists were able to identify microbial activities in soil, and isolated several Pseudomonas spp. and Paenibacillus spp. bacteria were found to be involved in biodegradation at high temperatures, around 10 to 42 oC. Ferguson and his team of scientists collected light diesel-contaminated soil from Old Casey, East Antarctica, and analyzed hydrocarbon levels using a septum injector and a flame ionization detector. Before the addition of nutrients, NH4Cl and K2PO4, for analyses, the subsamples were kept at -18 oC temperature. The temperature of the samples was then increased to 10 oC, and then to 42 oC. The identifiable micro-organisms were then isolated using their S16 rRNA gene sequences. Paenibacillus spp. is the most effective organism for biodegradation, but it occurred at high temperatures; close to 42 oC, with the aid of added nutrients. (Ferguson et al. 2008) This raises the possibility of decontamination of PHC effected soil layers by heating up the contaminated site. This modified temperature condition can be used to introduce the isolated bacteria to the environment. However, relatively high temperature treatments would be impractical to use in large contaminated sites. But this may be used for small contamination sites such as small fuel leaks in gas stations.
Conclusion
The biodegradation of contaminated soil is hindered or completely prevented by cold Arctic temperatures. It is nearly impossible for micro-organisms to survive, at least without the cyclic cold-warm conditions. Therefore, sub-arctic freeze-thaw conditions help species continue the biodegradation process in the region. Biodegradation accelerates if specific micro-organisms that can survive the freeze-thaw are introduced to soil in the sub-Arctic region to saturate contaminated areas. In areas where the temperature remains constant below freezing conditions, such as deep within the Arctic and Antarctic regions, bioremediation may facilitate an environment for natural organisms to thrive. With numerous research groups working on these techniques, hydrocarbons in soil soon may be treated by increasing the temperature of the soil using natural means or by artificially introducing microorganisms with IR properties to the contaminated sites. Application of bioremediation to the cleanup of petroleum-contaminated soil would be relatively easy and low-cost compared to current standards.
References:
Research Papers
Aitken CM, Jones DM, Larter SR. 2004. Anaerobic hydrocarbon biodegradation in deep subsurface oil reservoirs. Nature. 431:291-294. doi:10.1038/nature02922
Chang W, Klemm S, Beaulieu C, Hawari J, Whyte L, Ghoshal S. 2011a. Petroleum Hydrocarbon Biodegradation under Seasonal Freeze-Thaw Soil Temperature Regimes in Contaminated Soils from a Sub-Arctic Site. Environmental Science & Technology. 45(3):1061–1066. doi: 10.1021/es1022653
Chang W, Whyte L, Ghoshal S. 2011b. Comparison of the effects of variable site temperatures and constant incubation temperatures on the biodegradation of petroleum hydrocarbons in pilot-scale experiments with field-aged contaminated soils from a cold regions site. Chemosphere. 82(6):872-878. doi:10.1016/j.chemosphere.2010.10.072
Christner BC, Mosley-Thompson E, Thompson LG, Reeve JN. 2001. Isolation of bacteria and 16S rDNAs from Lake Vostok accretion ice. Environmental Microbiology. 3(9):570–577. doi: 10.1046/j.1462-2920.2001.00226.x
Ferguson SH, Powell SM, Snape I, Gibson JAE, Franzmann PD. 2008. Effect of temperature on the microbial ecology of a hydrocarbon-contaminated Antarctic soil: Implications for high temperature remediation. Cold Regions Science and Technology. 53(1):115-129. doi:10.1016/j.coldregions.2007.04.006
Walker VK, Palmer GR, Voordouw G. 2006. Freeze-Thaw Tolerance and Clues to the Winter Survival of a Soil Community. Applied and Environmental Microbiology. 72(3):1784-1792. doi: 10.1128/AEM.72.3.1784-1792.2006
________________
That’s it folks! I will publish the Review Paper, which will be on a different topic with much deeper analysis of the progress of science. I am thinking about writing this on nuclear mining or asbestos mining. But it could be too complicated with socio-political issues. We will see in the next few weeks how it will turn out.