5.3 Plume Tracers–Artificial Sweeteners (Acesulfame and Sucralose)

The artificial sweetener potassium acesulfame (C₄H₄KNO₄S) is used in a wide range of calorie-reduced food and beverage products and is now ubiquitous in most domestic wastewaters throughout the world (Buerge et al., 2009). This compound is relatively unique to domestic wastewater and occurs in septic tank effluent at concentrations typically in the range of 10-100 µg/L (Table 1). Acesulfame is relatively persistent during treatment in both municipal wastewater plants (Buerge et al., 2009) and in septic systems (Van Stempvoort et al., 2011a), as well as in surface water and groundwater flow systems (Buerge et al., 2009; Spoelstra et al., 2013; Spoelstra et al., 2017). Considering its typically high concentration in wastewater, compared to much lower background values in groundwater (e.g., ~10,000 times higher in the Long Point plume, Figure 3), it offers the potential to be a powerful tracer of septic system impact. Sucralose (C₁₂H₁₉Cl₃O₈) is another widely used artificial sweetener that also resists degradation, and occurs in domestic wastewater at concentrations similar to acesulfame (Table 1). It also has potential for use as a tracer (Oppenheimer et al., 2011). In the Long Point plume shown in Figure 3, acesulfame was used as a principal tracer because other potential tracers such as Cl^– were elevated in the background groundwater at this site, as a result of the use CaCl₂ as a dust suppressant on the campground roadways. Interference from other sources is a common problem associated with wastewater tracers (e.g., Figure 5) and highlights the usefulness of artificial sweeteners because they occur primarily only in domestic wastewater.

The use of specific artificial sweeteners has also changed over the past several decades and the presence or absence of specific sweeteners in groundwater plumes can serve as a rudimentary age dating tool. Potassium acesulfame has been in widespread use only since 1988 and sucralose since 2000. In a study of contaminant plumes and leachate at 15 landfill sites, Roy and others (2014) found that acesulfame was present in high concentrations and was the dominant sweetener at seven of eight active sites, but at seven sites that were decommissioned prior to 1990, saccharin (C₇H₅NO₃S) was the dominant sweetener and acesulfame was detected only at low concentrations.

More recently studies have revealed, that in some cases, acesulfame can be degraded during wastewater treatment (Castronovo et al., 2017; Kahl et al., 2018). This raises the possibility that acesulfame may also be subject to degradation in subsurface environments. Although a number of studies have demonstrated its persistence at relatively high concentrations, these studies do not preclude the possibility of slow degradation in certain environments, and further studies should be undertaken.