Could our caffeine habit cause aquatic stress?

Coffee beans. Image: Shunichi Kouroki | Flickr Creative Commons

A cup (or two) of coffee is a regular start to the day for many people. However, new research from the USA suggests that America’s caffeine habit may be contributing new stresses to the country’s aquatic ecosystems.

Our bodies don’t absorb all of the caffeine – the stimulant that can give us a pleasing ‘pep up’ – present in coffee, tea and many soft drinks, and as a result some caffeine is expelled in urine and faeces. Generally, sewage treatment plants remove a large proportion of caffeine from wastewater.

However, a long-term study in San Diego, USA, has found caffeine in remote streams far from urban areas and sewage plants, which may be contributing to ‘cocktails’ of multiple stresses impacting the stream ecosystems.

“When we started getting results, we realized it [caffeine] is way more prevalent than just from leaky sewer lines and septic systems,” said Carey Nagoda, a water resource control engineer for the San Diego Regional Water Quality Control Board. “So that was kind of a puzzle.”

Nagoda analysed nearly 100 samples from aquatic ecosystems across San Diego County and part of Orange County between 2008 and 2015. Sampling sites ranged from urban waterbodies which received both raw sewage and treated wastewater, to remote waterbodies far from human development.

The study found that caffeine concentrations in remote streams were as high as in some urban waterbodies. Around one-third of remote waterbodies tested positive for caffeine, with concentrations of between 0.032 to 0.662 micrograms per litre – similar to those samples taken around septic systems – detected.

“We were completely shocked by that,” Nagoda said. “What really ended up falling out was that the areas known for high recreational use – like fishing, horseback riding, hiking, camping – were the ones that had caffeine hits.”

A stream in rural San Diego County. Image: James Arnott | Flickr Creative Commons

Freshwater scientists often use caffeine as a ‘marker’ for pollution in water samples. Its presence often indicates leaking sewage systems, or other point source pollution, and the resulting presence of other contaminants. The results of Nagoda’s study therefore suggests that raw and untreated human waste is entering waterbodies in remote areas, most likely as the result of poor waste management practices.

Caffeine is known to be an ecological stress on aquatic ecosystems, particularly at high concentrations. The caffeine concentrations detected in Nagoda’s study are relatively low, and so unlikely to cross a ‘toxic threshold’ to cause widespread harm to aquatic organisms.

However, new research from coastal areas suggests that continued exposure to low concentrations of caffeine can place stress on estuarine crustaceans. A study by Zoe Rodriguez del Rey and colleagues exposed a common species of near-shore mussel to low levels of caffeine similar to those found in San Diego mountain streams. The mussels initially expended energy producing a protein designed to protect their DNA.

However, as caffeine levels were gradually increased – within a range detected in coastal waters – the mussels stopped producing the protective protein. The study’s authors suggest that the mussels are placed at greater risk of genetic mutation, as a result. “They get so stressed out at a cellular level that they can’t protect their DNA with this protein,” said Elise Granek from Portland State University, a co-author on the study.

Together, the two studies suggest that caffeine may be present in remote waterbodies, as the result of waste from recreational users; and that low concentrations of caffeine may have previously undocumented stress effects on aquatic organisms. However, there is still significant research to be undertaken on the topic.

As Granek suggests, “There are so many things that are stressing out organisms and ecosystems, it’s not on a lot of people’s radar to be looking at these [caffeine] compounds. It seems like people focus on things that they think are sexier compounds, like Prozac.”

Caffeine, then, might be seen as an emerging toxic stressor in need of further scientific attention, as Thomas Bruton and colleagues suggest in a 2010 article, “Although caffeine presents no large-scale threat now, further research is needed on the occurrence of caffeine in natural waters and its chronic toxicity to aquatic organisms.”