Sydney S. Choi – Life Science
Abstract
This study explores the efficacy of 254 nm UV-C light in sterilizing water samples from notable bodies of water in Vancouver, including Burnaby Lake, False Creek, and the Science World Wetlands. UV-C light, with its shortest wavelength among UV types (200-280 nm), is known for its strong sterilization capabilities. Water samples were exposed to UV-C radiation for 30 seconds, 1 minute, and 2 minutes, with microbial growth assessed post-exposure. Results indicated a significant reduction in microbial colonies with increased exposure time, particularly evident in the 2-minute exposure groups, which exhibited minimal to no growth. However, variations were observed across different trials and water bodies, suggesting factors such as initial microbial load and environmental conditions influenced outcomes. This research demonstrates UV-C light’s potential for effective microbial control in urban water bodies, with implications for public health measures in recreational water areas. Future studies should explore longer exposure times and larger water volumes to optimize sterilization protocols.
Introduction
Ever since the discovery of ultraviolet (UV) light in 1801, the scope of research in this area has become quite extensive with various uses in different fields including food processing, disinfection and air quality control (Barth, 1987). With different wavelengths of UV light determining the efficiency as well as the strength of the light, this tool has been applied for over a century. UV light is often categorized into three types: UV-A, UV-B and UV-C (National Center for Environmental Health, 2023). For the purpose of this research project, UV-C light will be utilized because it possesses the shortest wavelength at 200-280 nm and it has been proven to efficiently disinfect surfaces, water and air in large quantities in addition to controlling the spread of certain diseases (Ramos, 2020; Wideł et al., 2014).
A gap in the field of UV-C radiation used for water treatment is in bodies of water such as rivers, lakes and the ocean. Particularly in Vancouver where there is an abundance of lakes, the Fraser River passing through and access to the Pacific Ocean, these water bodies are unavoidable. In many bodies of water with public access, there are risks, often seasonal, but also potentially dangerous. In Vancouver specifically, beaches such as Jericho and Kitsilano can be closed down due to the harmful levels of Escherichia coli (E. coli) in waters (Vancouver Coastal Health, 2024).
This study aims to investigate the colonies of microbes that are present in notable bodies of Vancouver water, including Burnaby Lake, False Creek and the Science World Wetlands, as well as the ability of UV-C radiation to eliminate these microbes from water samples in 30-seconds, 1-minute and 2-minutes.
Materials and Methods
The experiment involved collecting water samples from three selected bodies of water: Burnaby Lake, False Creek and Science World Wetlands, exposing them to UV-C light, plating and growing microorganisms. The experiment consisted of two phases. The first phase being the Preliminary Trial where the original plans were tested and modified (Figure 1.1). Based on the Preliminary Trial, it was determined that the water samples would have to be exposed to UV before being plated with a quantity of 75 µL.
Figure 1.1. Preliminary Trial Procedure
The Experimental Trials consisted of one trial each week for three weeks. During the first week, the water samples were collected using identical mason jars with airtight lids. and additional data regarding the Temperature, pH level and Dissolved Oxygen level was gathered using a Vernier Kit each week prior to being exposed to UV. Then each of the three water samples were divided into four 50mL beakers for the four experimental groups they belonged to according to UV exposure length—a control group, 30-seconds, 1-minute and 2-minutes (refer to Figure 1.2 and Table 1). The control group (Group A) was immediately plated onto agar plates using pipettes to measure exactly 75 µL and sterile glass L-spreaders.
Figure 1.2. Experimental Trial Procedure
Table 1 – Groups and corresponding UV exposure length
For the remaining three experimental groups, each group was exposed to UV in respective increments of time. The 254 nm UV-C bulb from SUYOOULIN was attached on the inside of a heavy duty plastic storage box so that when flipped over, it would enclose the water samples. The light was turned on and off with the switch attachment. Group B was exposed for 30 seconds then plated immediately after. Group C was exposed for 1 minute and Group D was exposed for 2 minutes both of which were plated right after their exposure.
Once all of the experimental groups were plated, they were stored in the incubator at 25 degrees Celsius for 7 days. The following week, plates from the previous week were observed for results and the process was repeated for the next trial. The procedure took place over five weeks for a total of one Preliminary Trial and three Experimental Trials.
The results were measured through qualitative observations and rough estimates of colony sizes. The approximate number of colonies were compared across trials, groups and bodies of water.
Results
Initial data for temperature, dissolved oxygen and pH level for each trial and location are recorded in Table 2.
Table 2. Initial Data (Temperature, Dissolved Oxygen, pH) of Bodies of Water
The first trial produced many diverse colonies in plates from each body of water. Round yellow colonies were most common across all plates (Figs 2.1, 2.2 and 2.3). Group A plates, the control group, produced the most growth while Group D, the group that was exposed to 2 minutes produced little to no growth. In Group D of False Creek Trial 1, there are only two colonies and around 5 in Group D of Science World Wetlands. While this trend was clear in the False Creek and Science World Wetlands plates, Burnaby Lake produced plates that were quite similar across all four groups.
Figure 2.1. Burnaby Lake Trial 1 (from top left to bottom right) Group A, B, C, D
Figure 2.2. False Creek Trial 1 (from top left to bottom right) Group A, B, C, D
Figure 2.3. Science World Wetlands Trial 1 (from top left to bottom right) Group A, B, C, D
The second trial did not produce clear colonies in most plates . Many of the plates showed a white layer of growth and did not show any of the same results as the first trial (Figs 2.4, 2.4 and 2.6). The white layer was most visible in Burnaby Lake Group B and Science World Group C. However, in Science World Group B, one bright yellow colony was present along with a singular red spot. False Creek Group C presented one mould-like spot with a light outer-layer and darker center. The rest of the plates either had the white layer that covered the whole surface or had both the white layer and a few round colonies. There was no tangible trend between the four groups which received different time increments of UV-C radiation.
Figure 2.4. Burnaby Lake Trial 2 (from top left to bottom right) Group A, B, C, D
Figure 2.5. False Creek Trial 2 (from top left to bottom right) Group A, B, C, D
Figure 2.6. Science World Wetlands Trial 2 (from top left to bottom right) Group A, B, C, D
The third trial produced relatively consistent results across the different levels of UV exposure (Figs 2.7, 2.8 and 2.9). All three bodies of water showed the least number of colonies in Group C, 1-minute exposure. Additionally, all three bodies of water showed a white layer, much like layer in Trial 2, but at a smaller scale and most prominently in Group A. False Creek – Group A presented the most microbe growth while Burnaby Lake – Group C only presented 3 colonies. The results of the third trial are more similar to that of Trial 1 than Trial 2. However, there is a significant decrease of growth in the third trial. Burnaby Lake showed the least growth and False Creek had the most overall.
Figure 2.7. Burnaby Lake Trial 3 (from top left to bottom right) Group A, B, C, D
Figure 2.8. False Creek Trial 3 (from top left to bottom right) Group A, B, C, D
Figure 2.9. Science World Wetlands Trial 3 (from top left to bottom right) Group A, B, C, D
Discussion
Overall, Group A tended to have many more colonies than Group D. Greater lengths of the UV exposure produced less colonies. The results showed that UV-C radiation is effective in varying increments of time, with longer exposures producing better results of microbe elimination. Group D had little to no colonies and showed a significant decrease from Group C. Results from Group B and C were quite similar so it can be concluded that 30 second intervals are not very efficient, but are more efficient than no UV exposure at all. The results of the second trial may be considered skewed due to contamination as it is very different from the other trials and the initial data collected does not show any significant external indications as to why the results are so different (Table 2). However, according to Trial 3, where the white layer was present, but not fully covering the plate, it may be a different type of bacteria that grows in certain conditions. Table 2 shows that the pH was relatively higher during Trials 2-3 compared to Trial 1. Additional observations that show correlation between the initial data collected and the results of the plates include the abundance of growth in plate A of False Creek Trial 1 compared to the same plates from Science World Wetlands and Burnaby Lake. False Creek possesses a relatively higher pH level than that of the other two bodies of water as it is a saltwater body. However, the efficiency of the UV was not affected so it may be an indication on what type of water UV light is most efficient. Other patterns such as Burnaby Lake possessing the lowest Dissolved Oxygen Concentration with an average of 9.56 mg/L and Science World Wetlands measuring the coldest temperatures with an average of 11.0 degrees Celsius. However, these data points do not correlate to any observations of the plates.
Further investigation may include exposing water for longer increments of time as 2 minutes did not eliminate all colonies. Furthermore, testing UV on larger quantities of water and using UV-C lights with shorter or wavelengths. This procedure, at a larger scale, can be translated into the source of the samples where the UV-C radiation eliminates the microbes found in the water. This may be useful for conditions in the summer where warmer conditions nurture the growth of harmful levels of bacteria such as the aforementioned E. coli in Kitsilano Beach waters.
Some limitations of the experiment was the amount of water that could be tested on one plate. Only 50mL of each sample was exposed to UV-C light and only 75 µL was plated. Therefore, the efficiency of UV-C on a greater quantity of water is not guaranteed. Additionally, contamination is a source of error that is possible due to the frequent transfer of water samples. However, it is minimized through the sterilization of all materials and immediate plating after UV exposure.
Future uses for the results may be installing UV-C systems on beaches or on the hulls of boats to eliminate microbes that may be harmful to humans. The experiment did not investigate what types of microbes were present in bodies of water, but it was effective in eliminating them. Therefore, it is reasonable to conclude that UV-C lights can be effective when attached to boats or near beaches as it can eliminate potentially harmful microbes in bodies of water that people often swim in. There is no conclusive evidence showing adverse effects of UV-C light on marine organisms, but it is an important consideration when taking into account future applications of UV light in Vancouver bodies of water. In conclusion, Vancouver bodies of water showed a great volume of microbes in small quantities of water and UV-C light exposure for 2 minutes was the most effective increment for eliminating microbes.
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