Its widely understood that a key reason why life developed on Earth is because of water. A common definition of a habitable environment is one in which plenty of liquid water is available to sustain life. In short, we can’t live without water.
But there’s more to it than just the presence of water. We want our water to be clean and healthy so as to avoid risks to people and the environment from unwanted contaminants. With that goal in mind, numerous environmental monitoring studies have been conducted that look for various contaminants in water, and generally find some at trace levels.
For practical reasons, most monitoring studies target only a limited number of substances, meaning we only know what we looked for – not everything that might be present. Although these studies provide quite a bit of data, that leaves a gap in our understanding of the potential health and environmental impacts of real-life chemical mixtures in water.
As a step towards addressing these limitations, and the recently conducted an to provide more insight into the complex mixtures of contaminants present in streams.
Based on what we know from previous studies it isn’t a surprise that contaminants were found at low levels, but some of the findings may still be an eye-opener. For example, of the 12 most frequently detected contaminants, all but three are synthetic substances that were designed to be biologically active as pesticides or human drugs.
What Did They Find?
In short, they found a lot. All of the water samples contained at least one of the contaminants and some contained as many as 162. Even the four streams from undeveloped areas were found to contain some contaminants, although generally fewer contaminants compared to streams in developed areas.
The type of contaminants found is particularly interesting. The twelve most frequently detected contaminants, found in 66-84% of the streams, are all of anthropogenic origin, meaning they are the result of human activity.
Of these 12, all but three are synthetic substances that were designed to be biologically active as pesticides or human drugs. Perhaps most strikingly, one of the remaining three is estrone, which is a potent estrogenic hormone that is naturally produced in the human body.
Overall, 57% of the 406 substances detected are synthetic substances designed to be bioactive (e.g., pharmaceuticals, biocides). But bioactivity is not the exclusive realm of synthetic substances. Along with estrone, naturally occurring phytoestrogens, which are estrogenic compounds produced by plants, were also commonly detected.
The frequent detection of so many substances, in particular biologically active substances, may sound alarming. But low levels of a contaminant are not necessarily a concern and frequency of detection is somewhat of an artefact of the highly sensitive analytical methods that are available today. It’s not much of an exaggeration to say that you will find almost everything if your analytical method is sensitive enough.
Other factors beyond the level of a contaminant are critically important, in particular biological potency. The case of , which is well known to be weakly estrogenic, is a good example. As reported by and , t he estrogenic potency of BPA is about 100,000 times less than the potency of estrone, which is a prototypical estrogen and was found at a higher frequency in this study.
As a result of its low potency, a typical adult weighing 70 kilograms (154 pounds) would need to drink 21,472 liters (5,672 gallons) of water per day containing the maximum level of BPA detected (163 nanograms/L) just to reach the safe intake level. That’s especially not likely to happen since the maximum level was found in water.
To provide more context for the health and environmental significance of the contaminants, went a step further to measure biological activity in four standard assays. The assays, which measure estrogenic, androgenic and glucocorticoid activity, do not directly evaluate health or environmental risks, but provide information on the relative potential for risks. Importantly, the assays were run on the whole water samples, which essentially evaluates the actual chemical mixtures to which people or wildlife would be exposed from those water samples.
Estrogenic activity was detected in all but one of the water samples, the only exception being one of the streams from an undeveloped area, and the level of estrogenic activity varied considerably. Although the assays only provide screening data, some of the streams displayed estrogenic activity that is suggestive of risks to aquatic organisms, in particular fish.
But again, potency matters. As reported by USGS and EPA, estrogens naturally produced by the human body (primarily estrone) could explain nearly all of the observed estrogenic activity. Conversely, less than 1% of the estrogenic activity could be explained by the presence of all other estrogenic compounds, only one of which is BPA. Considering the low estrogenic potency of, only a fraction of that 1% can be attributed to
A question not specifically addressed in the new study is where do the contaminants come from? Although not within the scope of the research, anecdotal evidence reported by indicates that the samples with highest biological activity were collected downstream of wastewater treatment plants that contributed a significant amount of the streamflow. That evidence is consistent with other studies that report numerous contaminants in wastewater.
Once again, is an informative example. Although has been commonly found in wastewater, have also shown that is readily biodegraded in wastewater treatment plants, which substantially reduces the amount of released to the environment from treatment plants. Some of those same studies also show that many other contaminants are not efficiently degraded in today’s treatment processes.
The new study suggests that more research is needed to better understand what contaminants are in water and whether those complex mixtures pose any health risks. More importantly, the new data should help to focus further research and, eventually, help to prioritize actions to mitigate risks.