Use of Caffeine to Identify and Quantify Wastewater Contamination in urban Streams
Ghosh, Upal

Traditionally, bacterial indicators such as faecal coliforms have been used to detect and monitor the contamination of natural waters by municipal wastewaters. However, the reliability of such measures has been questioned because of their short time of survival and their limited source specificity. An ideal marker should allow the unambiguous determination of the source, quantification of the magnitude of the pollution, and should have a relatively steady rate of consumption and release into wastewaters. Caffeine is a constituent of a variety of beverages and food products and is widely consumed across the world. In a recent study by the USGS in 139 streams across the United States, caffeine was identified as a common contaminant with a frequency of detection of 70%.
In this research we are investigating the inputs and fate of caffeine in an urban stream (Gwynns Falls) in Baltimore City. We have developed a method for caffeine analysis using gas chromatography and mass spectrometry that gives us very low detection limits in water. Shown in Figure 1 are some of our measurements of caffeine concentration in various streams in the Gwynns Falls watershed. We measured high levels of caffeine (average of 1,030 ng/L) in water samples from one of the tributaries (Gwynns Run) that has a suspected contamination from a leaking underground sewer line. We show that using a simple mixing model we can calculate the flux of wastewater-contaminated stream flowing into Gwynns Falls. Based on laboratory biodegradation and photochemical degradation tests, caffeine appears to be reasonably conservative in the water column for typical travel times in an urban watershed near the coast. Inputs from this research are helping a larger collaborative effort among UMBC, Baltimore Ecosystem Study, and Baltimore City to understand the inputs and fate of wastewater-related contaminants in a highly urbanized watershed.

Keywords: caffeine, wastewater, urban streams, contamination

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