Team:Dalhousie Halifax NS/drylab/overview
Introduction
Ionic aluminum has been recognized as an issue in Nova Scotia since the 1980s due to the lack of limestone in our soil. We were interested in investigating the range of ionic aluminum concentrations in Nova Scotia waterwayss and which envrionmental factors may be related to variation in concentration. Our analysis focused on the following factors: (1) water pH, (2) water temperature, and (3) the sampling date. We performed exploratory data analysis on data collected by the scientists involved with the Centre for Water Resources Studies at Dalhousie University (link: http://centreforwaterresourcesstudies.dal.ca/) to better understand the range of ionic aluminum concentrations that our biosensor will need to be able to detect. In addition, these analyses helped us determine how different confounding factors affect the range of ionic aluminum concentrations that should be considered problematic. The data used for these analyses are available online as part of Dennis and Clair 2012 and Sarah MacLeod’s graduate thesis (2016).
Results
The ionic state of aluminum depends on the pH of the water. Therefore, the toxicity of aluminum is dependent on the pH of the water. Depending on the pH of the water, the window of safe ionic aluminum levels will increase or decrease. Based on existing literature, if the water is between pH 5.0 and 6.0 [1], the window of non-toxic ionic aluminum levels is 0 μg/L to 15 μg/L. When the pH is less than 5.0, the amount of safe ionic aluminum is increased to 30 μg/L [1]. The pH range which leads to the most toxic effects in fish has been identified as pH 5.2-5.4 [1].
Figure 1 shows the ionic aluminum levels present in different rivers in Nova Scotia that exceed the safe range of ionic aluminum concentration, which depends on the pH of the river water. Rivers with a pH above 5.0 should not have ionic aluminum levels that exceed 15 μg/L, those with a pH below 5.0 should not exceed 30 μg/L. Out of the 97 Nova Scotian rivers mentioned in this paper there are 14 rivers that have reached this unsafe range of aluminum concentration.
Looking at ionic aluminum levels from June 2015 to June 2016, ionic aluminum levels appear to be the highest from June to September, and lowest around December to March. When plotting the temperature and pH of the water over the same time-frame, the same trend appears. From these graphs the amount of dissolved ionic aluminum changes with the changing temperature, these changes will also lead to a change in pH of the water.
When looking at ionic aluminum levels alongside the pH and temperature of the water, the highest aluminum levels appear within a pH range of 4.25 to 5.5, with a water temperature between 15 and 20 degrees Celsius. There is no clear trend of the ionic aluminum increasing with either variable (although it can be noted that pH and temperature are evidently related).
To gain a sense of the overall distribution of ionic aluminum levels across the sampled rivers in Nova Scotia we assumed that the ionic aluminum levels are random samplings of the waters tested. There were samples taken from the same rivers, but for this analysis, they were assumed to be independent. Figure 4 shows that if we know the upper and lower bounds of ionic aluminum levels in Nova Scotia we can profile 98% of the water samples.
Conclusion
It is important that our biosensor is able to read toxic ionic aluminum levels of 0 μg/L to 15 μg/L (when pH of water is between 5.0 and 6.0) or 30 μg/L when the water has a pH of less than 5.0 as these levels are when the toxicity of aluminum becomes dangerous. After analyzing the relationship between the toxicity of aluminum, pH, and temperature of the water it becomes clear that the highest aluminum levels occur within a pH of 4.25 - 5.5 and a water temperature of 15 - 20 degrees celcius
References
[1] Dennis, I., & Clair, T. (2012). The distribution of dissolved aluminum in Atlantic salmon (Salmo salar) rivers of Atlantic Canada and its potential effect on aquatic populations. Canadian Journal Of Fisheries And Aquatic Sciences, 69(7), 1174-1183. doi: 10.1139/f2012-053
[2] MacLeod, S. (2016). Increasing Aluminum Levels In Southwestern Nova Scotia Rivers (Master of Science). Dalhousie University.
