Drugs in the water
Watertech Online
From Volume 31, Issue 5 - May 2008
by: David M. Bauman
The Associated Press (AP), after a five-month investigation,
recently published its findings1 about the prevalence of pharmaceuticals
(sidebar) in drinking water and drinking water sources. Sources for the
investigation included scientific reports, federal databases, environmental
study sites, treatment plants and more than 230 interviews.
The news agency´s reporters also surveyed the nation´s 50 largest cities and a
dozen other major water providers, as well as smaller community water providers
in all 50 states.
Before this year, the pharmaceuticals-in-drinking-water issue was only dimly in
the public consciousness. Water and wastewater treatment plants in the United
States typically do not remove pharmaceuticals, and the AP further points out
that even now the levels being found are usually measured in parts per
trillion, below the prescription dosage. Also, The US Environmental Protection
Agency (EPA) does not have pharmaceuticals listed in its drinking water
standards. So until now there has been little cause for
municipal water agencies to be testing for them or to be aware if they are
present.
But as a result of the AP´s report (disseminated by its hundreds of subscriber
news organization), consumers and public officials now have plenty of questions
(last month, a Senate subcommittee held hearings on the matter). To help water
treatment professionals be in a position to provide
some answers, Water Technology® recently took its own look at the issue.
How they enter water
Many people flush pharmaceuticals, over-the-counter
medicines, livestock and pet medicines, and personal care products down the
toilet or toss them into the trashcan. Other contributors are pharmaceutical
industries, hospitals and other healthcare facilities.
Since about 90 percent of oral drugs can pass though our bodies unchanged, many
of these drugs enter the environment through human and livestock waste. These
eventually make their way into private and municipal water supplies.
With the increasing popularity of groundwater recharge (adding water to an area
where it will supplement natural runoff or rainwater) in the
Molecular sizes and membranes
Because 2 percent or less of all water entering a household is ingested by
humans3, point-of-use/point-of-entry (POU/POE) water treatment for trace
occurrences of substances like pharmaceuticals would seem to be a very
cost-effective approach.
The Colorado School of Mines, a public engineering research university in
Golden, CO, studied the effectiveness of nanofiltration
(NF) and reverse osmosis (RO), among other technologies, to remove certain
pharmaceuticals from wastewater. Full-scale municipal facilities were used in
the study.
None of the investigated drugs were detected in tertiary treated effluents
after NF or RO. From this we can presume that at least some of the
pharmaceuticals can be removed by existing membrane technology.
An RO membrane removes species as small as about 0.000099 micron (µm). A look
at the sizes of a few random (non-pharmaceutical) organic molecules4, ranging
from 0.00086 µm to 0.0015 µm, suggests that RO technology would generally be
fine enough to remove them. But are all pharmaceuticals in this size range?
UF and ozone
Given the thousands of drugs and personal care items
on the market, it´s possible that some species would pass through the
smallest-pore membranes.
On the other extreme, many drugs incorporate larger reacting molecules like
enzymes. Most enzymes are in the range of ultrafiltration
(UF) membranes, 0.002 µm to 0.02 µm5. Proteins can have both positive and
negative charges6, so it´s possible they would be attracted to ion exchange
resins. And adsorbing anion resins might have a role in removing the larger
organic molecules.
In a German study7, granular activated carbon (GAC) and ozonation
used in a lab and in a water treatment plant, often in series, were very
effective at removing carbamazepine, diclofenac and bezafibrate. The
lab also showed that 3.0 milligrams per liter (mg/L) of ozone cut primidone levels by nearly 90 percent. Although neither GAC
nor ozonation at any concentration was fully
successful with clofibric acid separately, the two in
combination cut levels of the drug to below the limits of detection during
plant testing.
Activated carbon, ozone, UV
GAC is effective because carbon can pick up a broad category of compounds, and
many pharmaceuticals have components like benzene rings or amine groups that
enhance their ability to be taken up by the activated carbon7.
Shane Snyder, research and development project manager for the Southern Nevada
Water Authority, testified in mid-April to a US Senate
subcommittee about the pharmaceuticals issue on behalf of the American Water
Works Association (AWWA), the water utility trade group. In an interview with Water
Technology®, he said the powdered form of activated carbon can be even more
effective if used properly.
He said ozone´s effectiveness is tied to its ability to chemically attack the
pharmaceutical molecules. For example, it can oxidize different kinds of
functional aromatic bonds (forces binding certain carbon-based atomic
structures within molecules) in pharmaceuticals.
In the German study, Ternes states that his research
has shown ozone capable of easily oxidizing 90 percent of 51 different
pharmaceuticals. It is particularly effective with compounds with amine groups
and phenolic hydroxyl groups.
Advanced oxidation processes using a combination of ozone and UV or ozone and
hydrogen peroxide8 have likewise shown promise in removing some of these
contaminants. The Water Quality Association (WQA) has also included
distillation products on its list of promising pharmaceutical-removal
technologies.
Solutions, and cautions
Drugs contain organic chemicals, volatile organic chemicals, inorganic
chemicals, plant products, proteins and amino acids, and more. There are drugs
that are hydrophobic (water-repelling) and hydrophilic (water-attracting). How
will hydrophobic drugs react in a water environment? Given this, it´s possible
that some pharmaceuticals will require one type of treatment and some another.
Looking at bottled water and home drinking water systems, the AP said that some
bottlers simply repackage tap water and that neither bottlers nor manufacturers
of treatment equipment test for pharmaceuticals. Strictly speaking, this is
true, but AP should have also noted that there are bottlers that use, among
others,
Given the very large number of pharmaceuticals and the wide variety of chemical
compounds found in them, it´s clear that one particular treatment is probably
not going to remove them all. Most studies have looked at only two to six
drugs, so it would be difficult to promote any single POU/POE technology or
product as a panacea for pharmaceutical removal.
Studies on this subject to date include many qualifiers. In the example above,
for instance, both activated carbon and ozonation
failed to remove one drug, but they were successful when used together. Testing
so far has included
A favored approach
Removal of pharmaceuticals today could be likened to the issue of removal of
volatile organic chemicals (VOCs) 20 years ago. At
that time, very little was known about VOC removal and there was no product
testing. Now we know that we can be relatively successful at removing VOCs, but some treatments work better on some VOCs than on others.
POU/POE will likely be a favored treatment approach for pharmaceuticals due to
the economy of treating only the water used for drinking as opposed to entire
municipal supplies.
There is now little reason for panic due to the low concentrations of
pharmaceuticals found. However, future research may well show the cumulative effects
of drugs in the body; it will certainly show more about the relative health
risks and prevalences of specific ones. When that
happens, there will undoubtedly be tested products at the ready, at least for
the most prevalent and potentially harmful drugs.
Notes:
David M. Bauman, CWS-VI, CI, CCO, is technical editor of
Water Technology®, author of the magazine´s monthly “Professor POU/ POE” technical
advice column, and a water treatment consultant in
dp-bauman@sbcglobal.net.