SOURCE: Spoelstra, J., Senger, N. D., & Schiff, S. L. (2017). Artificial Sweeteners Reveal Septic System Effluent in Rural Groundwater. Journal of environmental quality, 46 (6), 1434-1443. Doi:10.2134/jeq2017.06.0233
What is septic tank effluent and why do we need to track it?
In some rural areas sewage from homes is treated on site rather than at a centralized wastewater treatment plant. In the case of onsite treatment, most homes have what is called a septic system that consists of an underground treatment tank. Wastewater from the house is treated in the tank and released into the soil where it will eventually meet up with groundwater (Figure 1). Therefore, septic tank effluent may contaminate groundwater with pollutants such as nitrogen and pharmaceuticals. This could be harmful to human health if an area relies on wells for their drinking water and septic systems for their wastewater treatment, as pollutants from septic effluent could contaminate the drinking water.
As a result, scientists have been looking for methods to determine if groundwater has been impacted by septic systems. For example, studies have examined the concentrations of fecal coliforms in groundwater (Francy et al. 2000; Goss et al. 1998). Fecal coliforms are bacteria that live in the digestive tracks of humans and animals and are therefore found in septic effluent. While these studies have found fecal coliform present in groundwater in Ontario and the U.S., it does not guarantee that the water was impacted by septic contamination. This is because the fecal coliforms may be from animals instead of humans, especially in areas that have livestock operations.
The researchers in this study (Spoelstra et al. 2017) focused on a method that used
artificial sweeteners (Figure 2) to track effluent from septic systems. Nowadays, artificial sweeteners can be found in all kinds of products from diet soda to toothpaste. As a result, they are commonly found in our waste. There are several advantages of using artificial sweeteners to track septic tank effluent. To start, they are almost exclusive to human waste (animals are very rarely fed these products). In addition, they do not break down in the environment. In fact, artificial sweeteners have already been detected far from their sources of emission and are widespread in rivers, lakes, and groundwater.
How did they do it?
The researchers examined the concentrations of four commonly used artificial sweeteners in a rural setting in Toronto, Canada. The aquifer they collected samples from functions as a source of water for private wells and receives treated effluent from septic systems. The scientists collected samples from private domestic wells and seeps, which are places where groundwater reaches the soil surface. They used the concentration of artificial sweeteners in the samples to determine what percent of the water came from septic effluent.
What did they find?
The scientists found that the sweetener Acesulfame was the most commonly occurring in the samples. Acesulfame also had the highest concentrations in both seeps and wells. This is not surprising because Acesulfame is commonly used as an artificial sweetener in Canada and has a strong resistance to degradation in the environment.
By measuring sweeteners, the researchers estimated that up to 13.6% of the wells have 1% or more of their water coming from septic systems. While 1% may not sound like a lot, the wells with the two highest Acesulfame concentrations were estimated to receive 39% and 100 % of their water from septic effluent. This demonstrates that septic effluent in drinking water may pose a risk for some homes, but not others. Therefore, the researchers suggest that testing for artificial sweeteners can help determine which wells should receive additional testing.
To summarize, artificial sweeteners are approved for human consumption, so their presence in drinking water isn’t bad. In fact, these sweeteners can act as useful indicators that septic system effluent is in drinking water. This is important because that effluent might contain other contaminants such as pathogens, nitrates, and pharmaceuticals that are harmful to human health. The researchers in this study believe that artificial sweeteners can serve as a screening tool to identify groundwater that may be impacted by septic effluent and should therefore receive further testing.