It’s
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, 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. 

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.

Perhaps
counterintuitively, contaminants that we frequently hear about may not be commonly
found in water.  For example, bisphenol A
(BPA), which is a synthetic chemical that is primarily used to make
polycarbonate plastic and epoxy resins, has been a popular topic in the media
for years.

Yet
BPA was found only at very low levels, when detected at all, in less than 40%
of the streams.  Even at the highest
level detected, which is well below 1 part per billion, an adult would have to
drink over 21,000 liters of water (over 5,600 gallons) per day just to reach
the safe intake limit for BPA set by EPA. 
Obviously that’s not even remotely possible, indicating that the amounts
of BPA found are not likely to be a human health concern.

To
begin to get a handle on how these complex mixtures of chemicals may interact
with biological systems, the researchers also tested whole water
samples in a series of screening tests to measure biological
activity.  With only one exception, all
of the water samples tested positive for estrogenic activity, which was the
most common type of biological activity detected.

But
this result too may be counterintuitive. 
The researchers reported that nearly all of the observed estrogenic
activity could be attributed to naturally produced hormones, in particular
estrone, which is known to be a potent estrogen and is one of the top 12 most
frequently detected contaminants.

Conversely,
even though BPA is known to be weakly estrogenic, BPA contributed well under 1%
of the observed estrogenic activity. 
Again, these results indicate that BPA in water is not likely to be a
human health concern.

Why Did USGS and EPA Do The Study And
What Did They Do?

As
noted by USGS and EPA, “[c]hemical-mixture exposures in streams are global
concerns.”  For that reason, hundreds of
studies have been conducted by scientists worldwide to measure levels of
various contaminants in all types of water bodies (e.g., rivers, streams,
lakes, oceans) as well as in potential sources of contaminants (e.g., wastewater
treatment plants).

These
studies document the presence of a wide variety of contaminants in water,
generally at very low levels.  Both
natural (e.g., human and animal hormones, phytoestrogens) and synthetic (e.g.,
pharmaceuticals, pesticides, industrial chemicals) substances are frequently
found.  For practical reasons though, most
studies typically target only a small number of substances. 

While
the resulting data is useful, it does not provide a complete picture.  More complete knowledge is needed to
understand the full scope of contaminants in water, the potential human and environmental
health risks of these complex mixtures, and to set priorities for the most
appropriate actions to mitigate risks.

To
begin to address the limitations of previous targeted studies, USGS and EPA
designed a study that combined two approaches to 1) measure levels of a wide
range of contaminants in water, 2) assess biological activity of the
contaminant mixtures, and 3) relate biological activity to the contaminants
present.  In the first part of the study,
surface water from 38 streams nationwide was analyzed for 719 substances.   In the
second
part,
biological activity of the water samples was monitored in four bioassays that
measured estrogen, androgen and glucocorticoid activity.

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.

What Does It Mean?

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 BPA, which is well known to be weakly estrogenic, is a good example.  As reported by USGS and EPA, the 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 for BPA set by EPA.  That’s
especially not likely to happen since the maximum level was found in water from
the Chicago Sanitary and Ship Canal, which you’re not likely to drink at all.

To
provide more context for the health and environmental significance of the
contaminants, USGS and EPA 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 BPA, only a fraction of that 1% can be attributed
to BPA.

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 USGS and EPA
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, BPA is an informative example. 
Although BPA has been commonly found in wastewater, many
studies have also shown that BPA is readily biodegraded in
wastewater treatment plants, which substantially reduces the amount of BPA 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.