The days of rivers catching on fire from high levels of pollution are long gone. These days Americans almost take it for granted that the rivers, streams and lakes around us are safe and clean. Nevertheless, there are still concerns about the potential for health risks to people and the environment from trace levels of contaminants in water.
Numerous studies have documented the presence of various contaminants at very low levels in natural waters worldwide, but these studies don’t give us a complete picture. We only know what we looked for – not everything that might be present – and, we may not know much about the potential health impacts of the contaminants that are found.
To start addressing these limitations, the U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency (EPA) recently conducted an in-depth study to provide more insight into the complex mixtures of contaminants present in U.S. streams.
In the first part of the study, the researchers analyzed water from 38 streams nationwide for 719 substances. Perhaps not surprisingly, they found 406 of the substances in at least one stream. All of the water samples contained at least one of the substances and some contained as many as 162.
While bisphenol A (BPA) is frequently mentioned in media stories, in the real world it was found only at very low levels in less than 40% of the streams. Levels so low, in fact, that a typical adult weighing 70 kg (154 pounds) would need to drink 21,472 liters (5,672 gallons) per day of water containing the maximum level of BPA (163 parts per trillion) just to reach the safe intake level for BPA set by EPA. That’s especially not likely to happen since the highest level was found in water from the Chicago Sanitary and Ship Channel, which is a primary pathway for sewage from Chicago to eventually reach the Mississippi River.
Perhaps more surprising is that many of the more commonly found contaminants are synthetic substances that were designed to be biologically active (e.g., as pesticides or human drugs). And one of the top 10 in frequency of detection is estrone, which is a potent estrogenic hormone that is naturally produced in the human body.
The study didn’t specifically address how the contaminants got into water. However, some anecdotal evidence indicated that the samples with highest biological activity were collected downstream of wastewater treatment plants that contributed a significant amount of the streamflow.
Although BPA and many other substances are frequently found in wastewater, it’s well-known that BPA is readily biodegraded in modern wastewater treatment plants, which substantially reduces the amount of BPA released to the environment. Studies also show that other contaminants are not efficiently degraded in today’s treatment processes.
In the second part of the study, biological potency becomes particularly important. The researchers monitored biological activity in the water samples with four bioassays that measured estrogen, androgen and glucocortinoid activity. Estrogenic activity was found in all but one of the water samples but, as noted by the researchers, almost all of the activity could be explained by the presence of estrone.
Less than 1% of the estrogenic activity could be explained by the presence of other estrogenic substances, and only a fraction of that can be attributed to BPA. The low contribution of BPA is due to its low estrogenic potency, about 100,000 times less potent than estrone according to the researchers, and the low levels at which it is found. Taken together, the data suggest that the very low level of BPA found in some streams is not likely to be a health concern.
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.
If you’re interested in this story, more blogs related to BPA are available at AmericanChemistry.com.