Sweet tracer: Sucralose in drinking water is a marker for human activity

Human contributions to water quality

The waters of the world reflect human activity on land, becoming tainted with a wide selection of chemicals as industrial activity increases over the years. They are also an indicator of social activity, with the discovery of drugs of abuse in waters from urban catchment areas.

A second class of anthropogenic compounds which have been detected in wastewater, surface water and tap water in Europe are artificial sweeteners like acesulfame and sucralose. Modern wastewater treatment plants are not geared up to remove them, so they are emitted in the waste streams to the environment.

Sweeteners originate not only from foods, but also from personal care products and pharmaceuticals preparations, so they are safe for human consumption. However, the effects of chronic exposure to sweeteners and trace organic compounds in water have not been established.

Similar studies in North America have detected artificial sweeteners in marine and coastal waters, wastewater treatment plant effluents and groundwater. In particular, the consistent presence of sucralose has led to its proposal as an indicator of the presence of wastewater in surface waters.

In order to support this proposal, scientists in the US have conducted a wide-ranging study on the presence of sucralose in water associated with wastewater treatment plants. Douglas Mawhinney and colleagues from the Southern Nevada Water Authority, Colorado State University and the University of Arizona measured sucralose in the source, finished and distributions system (tap) water of 19 wastewater treatment facilities.

Sucralose persists following water treatment

The source waters employed at the various plants included reservoir water with no known wastewater input, groundwater, and surface waters known to have wastewater input. A range of wastewater treatment schemes were also in place across the plants.

Each of the water samples was extracted by SPE to enrich the sucralose by a factor of about 1000 before addition of a deuterated derivative of sucralose for use as an internal standard. The extracts were analysed by LC/MS analysis with electrospray ionisation in negative-ion mode. The sweetener was quantified by isotope dilution, using the deprotonated molecule and the chloride product ion. The lower limit of detection was set at 10 ng/L.

Sucralose was almost omnipresent, being found in 15 of the 19 source water samples, including all of those impacted by wastewater, where the measured levels were the highest of all. Other source waters that had recreational uses like boating or swimming had lower levels of sucralose, which probably originated from human waste and foodstuffs entering the water. Tellingly, those waters with no wastewater input contained no detectable sweetener.

The observed concentrations, at 47-2900 ng/L, agreed with published data for US surface and ground waters but were higher than European data.

The finished water from the treatment plants was still highly contaminated with sucralose, with an average removal rate of just 12%. The most successful plants employed chlorine dioxide and UV treatment, suggesting that advanced oxidation processes are the best way forward for sucralose destruction.

The researchers also tested the distribution water from a subset of the systems after it had travelled "relatively far" from the treatment plant. In all cases, the sucralose concentrations were unchanged, demonstrating widespread exposure of the US population via drinking water. The highest rate of exposure based on the results would be 48 µg sucralose daily.

Indicator for human influence on water supply

The apparent persistence of sucralose in the water systems prompted Mawhinney to examine its suitability as a marker of the influence of wastewater on source water and tap water. Its concentration was measured over 11 months at one wastewater treatment plant using the same mass spectrometric method.

Over the whole period, the concentrations of sucralose in both types of water were fairly stable, indicating a regular contribution of the sweetener to the source water and a constant level of removal in the treatment process. The removal rate averaged 20%, so the treatment regime involving chlorine and ozone was not particularly effective.

However, this behaviour makes sucralose a good indicator for the influence of human activity on source water and tap water across the US, both for wastewater and recreational water inputs.

The anxiolytic drug meprobamate is another persistent compound in wastewater treatment plants. The researchers noted that the ratio of sucralose to meprobamate in source and finished water was relatively constant, so argued that sucralose could also be used as an indicator for the presence of the drug, since both originate from human activity.

But for a single indicator, sucralose is preferred because it has been estimated that usage of the drug will increase in future, so its concentration in the source water will not be constant.

So, the poor performance of wastewater treatment plant regimes for removing sucralose means that the sweetener can be employed as an indicator of anthropogenic influence on the water systems in the USA.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.