December 23, 2024 • 21 mins
Modern Americans benefit from centuries of improvements in drinking water safety. In this episode of the "NSF's Discovery Files" podcast, Julian Fairey, associate professor in the University of Arkansas Department of Civil Engineering, discusses how drinking water is treated and how he helped identify a disinfection byproduct.
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(00:03):
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
The United States
has benefited from centuriesof improvements in drinking water safety.
And most Americans can trustthat clean water comes from their taps.
But contaminants can come into systemsfrom harmful bacteria
leaching of lead, copper and microplasticparticles from plumbing hardware,
(00:26):
or even human error.
When a clean water line is accidentallyconnected to a contaminated one,
we are joined by Julian Fairey, associateprofessor in the Department of Civil
Engineering at the University of Arkansas,whose research group focuses on drinking
water treatment and understandingthe natural organic matter
and disinfection byproducts that resultfrom water treatment processes.
(00:46):
Professor Fairey,thank you for joining me today.
Pleasure to be here.
Thinking about the water systema little bit as we ease into it.
Can you talk about the general structureat all, like for people
that don't know anythingabout how it works?
Are these broken down by region or cities?
Certainly both. In some cases.
Most certainly big cities have multipledrinking water treatment plants.
(01:08):
Some regions that are more ruralregions will have sort of centralized
drinking water treatment plantthat supplies a fairly vast area.
How I think of drinking water treatmentbeing broken down
is by groundwater or surface water.
Groundwater treatmentis typically a little bit more simple.
We think of, you know, kind of well water.
If you grew up in the countryas being fairly high
(01:32):
quality water,not a lot of particles in it.
And so the treatment can be quite minimalin that regard.
And, you know, there's many cities.
Houston, for example, usesa lot of groundwater wells.
They blend that with surfacewater sources.
And when you do that surfacewater in general, I mean,
they're they're exposed to the atmospherearound to different elements.
And that's where we think of a little bitmore advanced treatment
(01:54):
being absolutely necessaryin order to protect human health.
So how do we treat water?
Well, reallywe want to get the stuff out of it.
And so if you hold up a water glass, it'sgot things floating around in them.
You're not going to have a sensethat's safe
and that's a good instinct to adhere to.
And so we want to get particles out of it.
And we want to stabilize itfrom a microbiological standpoint as well.
(02:18):
And so really what that requiresis making these particles
when they come into a water
treatment plant from like a river sourceor a lake source, for example.
The particles are generally pretty small.
And so what we typically do is we addcoagulant and mix at a relatively gentle
rate in order to make bigger particlesform that subsequently settle.
(02:40):
And we can filter out.
In addition, we add chemical disinfectantsto kill bacteria,
inactivate microorganisms,and when we send us the water
through a series of pipes that we refer toas the distribution system
that enters all our homes.
And so we can basically drinkclean water on demand.
What kind of chemicals are we using inthe process to disinfect drinking water?
(03:02):
There are a number of chemicalsused in in the United States.
We break those chemicals into whatwe refer to as primary disinfectants.
So disinfectants are used in the drinkingwater treatment plant
and then secondarydisinfectants, chemicals
that are used within the drinkingwater distribution system.
And so these chemicals can be very similar
or a little bit different between primaryand secondary disinfection.
(03:24):
The most common disinfectant used in theUnited States and worldwide is chlorine.
People in my companyusually refer to this as free chlorine,
because we distinguish free chlorinefrom the second
most common type of disinfectant,which are chloramines.
They're often referredto as combined chlorine.
Some chloramines are created by reactions
(03:45):
between free chlorine and ammonia.
And so most drinkingwater systems in the United States
use free chlorineas a primary disinfectant.
The majority of water systems also usefree chlorine as a secondary disinfectant.
But about one third of water systemsin the United States
use chloraminesas a secondary disinfectant.
(04:08):
And so, let's say between free chlorine
and chloramines, those make up the bulkof our drinking water.
Disinfection in the United States.
There are utilities that use other,certainly primary, disinfectants.
Ozone is a fairly common one.
Chlorine dioxide is somethingthat's used in many places
around the United States, includingwhere I live in Fayetteville, Arkansas.
(04:30):
But in terms of drinking water,disinfectants in the distribution system,
secondary disinfectantsis or typically free chlorine chloramines.
And there may be a small handfulof systems that use chlorine dioxide.
So all of these processes have byproducts.
And I understand that's quite a bitof what you've studied over the years.
Can you talk a little bit aboutsome of these byproducts that result?
(04:52):
Sure.
And so all these disinfectants,they inactivate, microorganisms,
which is their primary purpose,but they're also oxidants,
and they react with naturally occurringorganic materials
that are naturally presentin drinking water.
Some of these reactions resultin the formation of unintended compounds
(05:13):
that we just generically referto as disinfection byproducts.
This was first realized,and I would say the mid 1970s, where
there were some studies doneto show that free chlorine,
if you just add it to a drinking water,reacts with this organic matter
that's naturally present in the drinkingwater systems, and it forms a compound
(05:34):
called chloroform, chloroformas part of a group of trial methods.
And so it was realized in the earlyor in the mid 1970s
that these unintended compoundsformed subsequently,
through toxicity testsand things like this, we realized, okay,
we need to regulate these groupsof of disinfection byproducts that formed.
(05:56):
And so you see, in the mid 1990s,we regulated tri, our methane,
and another group of disinfectionbyproducts called our cedar gas.
It's in these are two groupsof disinfection byproducts that on a mass
basis form at the highest concentrationsin chlorine, emanated waters.
In the last 50 years, we found,
(06:17):
you know, 6 to 700 disinfection byproducts
forming out of all sortsof combinations of disinfectant regimes,
natural organic matter types,as well as like different
background ions that are in waterlike bromide and chloride.
That's one group of disinfectionbyproducts.
The other group that I've been moreinterested lately are products that form
(06:40):
from the disinfectant alone,so they don't need natural organic matter
or anything other than the disinfectant.
We've long known when chlorine dioxide,for example, decomposes, it
forms chloride.
And this is regulatedin our drinking water systems.
But there's been this mystery compoundassociated with chloramines that we know
that's formed.
(07:01):
We've known this since 1980,but we haven't been able to identify.
And that's what my work in the lastten years has been about, trying to go
about identifying this compoundthat is a natural decomposition product.
Of Corning disinfection.
So can you talk about thatchlorine nitride anion.
Why was that of interest or a mystery?
(07:21):
The story starts back in 1980.
There was a PhD thesis out of Cal Berkeleythat showed when we're monitoring
the two principal disinfectant compounds
in chloramine systems,monoclonal amine and dichloromethane.
There was two methods at the timeto determine their concentrations,
and initially
these two methods were giving the sameresult for multiple mean and dichotomy.
(07:44):
But over time these two methodsdiverted from one another.
One of the methodswas based on new absorbance,
and so whatthey were able to determine was,
as chloramines are breaking down,
they're forming this compound that createsan ultraviolet interference
with one of these methodsthat they were using.
(08:04):
And so they knew this unknown compoundwas forming that subsequently
became known to people in my fieldas the unidentified product
was a stable productthat formed during quorum decomposition.
And it was just a mystery of whatthis thing, one was.
A lot of work done in the 1980sand 90s, primarily by Rich Valentine
(08:27):
out of University of Iowa,that was aimed at trying to identify
this mystery compound,and they did a lot of really innovative
work in chloramine chemistry,and that's the work we built on.
And so they developed methods to form
this compoundat relatively high concentrations.
(08:47):
When you want to try to identifysomething,
that's one really effective strategyfor going about that, transform
this thing at very high concentrations,see if we can get some other
analytical techniques to it.
And so they formed this mystery compoundthat they weren't able
to determine its molecular formulaor its structure.
But they were able to break it down
(09:12):
and showedthat contained chlorine and nitrogen.
So that was a hint.
They also showed that materialsthat are in point of use filters,
like a Brita filter, for example,was able to destroy this compound.
And so that was a useful insighton the treatment side of things
that people don'twant to be exposed to this compound,
(09:32):
perhaps a home water filterwould be effective in removing it,
but they ultimately weren't ableto identify this compound.
And so when I got into chloraminechemistry
work, I was I was basically a PhD studentat the University of Texas at Austin,
and I was looking at how Chloraminesreacted with activated carbon.
(09:53):
It was for a completely different process
unrelated to this mystery compound,but it got me into chlorine chemistry.
And subsequently, when I startedmy faculty job here at the University
of Arkansas,I was looking for a fundamental way
to explain the formationof a group of disinfection
byproducts and chloramine systemsthat are called nitrosamine.
(10:14):
Together with a colleague of mine,a friend from graduate school,
his name is Dave Warmand he works at USP in Cincinnati.
We set about trying to explain hownitrosamines formed in chloramine systems.
So I got a grant funded by theNational Science Foundation back in 2020
to kind of better explainhow nitrosamines form in Corning systems.
(10:35):
And what we showed waswhen chloramine means
decompose,they form reactive nitrogen species.
And this was a big leap forwardin the science of causing decomposition,
really filled in a major gapfrom the original work done
by Valentine and his colleaguesback in the 1980s and 90s.
So what we showed specifically waswhen chloramines decompose under drinking
(11:00):
water conditions,McCormick decomposes to dichotomy,
and then dichotomy undergoes hydrolysis,just meaning it reacts with water
to form nitro oxo and my Troxellis this really interesting
reactive nitrogen speciesthat has a number of functions, both like
physiology, but also in, as it turns out,in our chloramine systems.
(11:23):
And what we showed was my outsole reactswith dissolved oxygen,
which is present in all our watersjust naturally, and forms another
reactive nitrogen species called pyroxenenitrate.
And proxy nitrate, as it turns out, decaysrapidly to things that we
are really familiar with in drinking watertreatment nitrate in nitrate.
But along the way, it forms a whole hostof reactive oxygen and nitrogen species.
(11:47):
And turns out some of these specieswere key in the formation of NDma.
These nitrosamine.
We also realized in this work
that proxy nitrate decomposition products
were involvedin the formation of this mystery compound.
So we did some studies under both
(12:07):
low and ambientdissolved oxygen conditions
that showed this mystery compoundwas mitigated under low D.O.
conditions, meaning that proxy nitrateor its decomposition
productswas likely involved in its formation.
So this kind of brought us back to seekingto identify this mystery compound now.
And so, as you may get a sense, thisthe chemistry of this system
(12:31):
is starting to get pretty complicated.
And this happened to coincidewith my sabbatical
year here at the University of Arkansas.
And I was like,I need to solve this problem.
And so where could I go to do this?
One of the reviewers or so on one of our
NMA papers was Chris McNeil.
He is a professor at Zurich,and he had reached out just sort of
(12:55):
with a congratulatory message regardingone of our papers after it published.
Very nice.
And this kind of
started up a conversation of, hey,can I come over there and do a sabbatical?
Or maybe look at this problemof this mystery product.
He's more of a trained chemistand I'm more of an environmental engineer.
And so this worked out. It was great.
But I went over there and spent a yearin Switzerland
(13:19):
trying to identifythis, this mystery compound.
And Chris had a an analytical chemistin his group in doing this
sort of it's who is a postdocstill is a postdoc in his group,
and she just has really stronganalytical skills.
And so we set out trying to identifythis compound with some of the equipment
(13:41):
over in Switzerland and Chris's laband in a neighboring lab called AVL.
And that's really where the story startedgetting interesting
in terms of having some successin identifying this compound.
So now that you kind of know what it is,
what becomes the next steps into like,I don't think you know that much
(14:01):
about how toxic it isor what its impacts are on people,
like, what are kind of the next stepsthere with that research?
So as we speak, I have a
PhD student in my lab trying to producevery high quantities of chlorine.
Nature might I anion for toxicity testing,
we needed to producevery high concentrations
of this compoundfor some of the spectroscopy work
(14:22):
that went into the identificationof the chemical structure by NMR and Ftir.
But we need even larger quantitiesfor toxicity testing.
And so we're trying to scale upthose methods now
both in terms of producing this compoundbut also purifying it.
We want to make sure that it'sonly this compound in toxic retests.
(14:43):
And so I'm not a toxicologist,but I'm collaborating with colleagues
at USDA as well as in Switzerland
and in other labs in order to assessthe toxicity of this compound.
So that's one major effort that'songoing of press we're interested in.
Hey, how toxic is this thing?
What what does this mean for us?
And I think that'sa very important question to answer.
(15:06):
The other thingthat was interesting for us
was so as partof the publication in science,
we sampled ten water systemsfrom across the United States.
So these were systemsthat all use chloramine disinfectants.
And so we found this compound called my.
And I'm in all system.
There was 40 total samples.
We found it in all 40 samples.
(15:27):
But we found it at really a sort of a vastrange of concentrations,
which was somewhat unexpected.
All the way from like one microgramper liter up
to 120 micrograms per liter.
And so since chlorination right at nineis the decomposition product of cornyn's,
requirements are all added at aboutthe same amount in our water systems.
(15:49):
We were a little bit puzzledas to why there was such a large range
of concentrations.
And so what I'm doingis trying to explain that
there must be some propertiesof these water systems,
some other chemistrieswithin the water that maybe quench some
of the intermediates that are involvedin the formation of this compound
(16:11):
or enhance its formation in some way.
We think it's relatively stable.
Once it forms, we don't thinkit's going to decompose a lot.
But what are the sort of the keywater chemistry parameters
that lead to relatively lowformation versus high formation?
Regulated disinfectionbyproducts have standards at trial,
(16:32):
and these things are regulated at a masksome of 80 micrograms per liter.
How low acetic acidor at 60 micrograms per liter.
So we're finding,
you know, core nature might anionbetween 1 and 120 micrograms per liter.
And so if this proves out to be toxic,logically relevant, likely there'll be
some threshold at which it'll be toxic and
(16:54):
is that level 500 micrograms per liter?
Is it at 100 micrograms per liter?
Is it at 50 micrograms per year?
We don't know.
But right nowwe're interested in understanding.
Well, why are some systems formingrelatively low concentrations.
Why are others formingrelatively high concentrations?
You know, if it turns out thatthis is toxic, logically relevant?
(17:15):
Well,if we understand how it's forming better,
we can then, you know, advisechloramine systems.
Okay.
You know, if you want to controlthis product, here's what you do.
And that's kind of the workthat is ongoing now
along with the toxicity testing.
And you said something as simple as a pumpwater filter can remove it
from that water system.
What was shown by Rich Valentine and hiscolleagues is back in the 1980s and 90s,
(17:39):
when we still refer to this compoundas the unidentified product.
He showed that the unidentified productcan be removed by activated carbon,
which is a materialthat's in point of use filters,
typically in a fridge or pitcher filterthat could be in your house.
We haven't validated that yetwith chlorination might A9 specifically.
So we think that should work.
(18:00):
There's testing that's about to startat a US EPA in Cincinnati in this regard.
Evaluating point of use filtersfor chlorination Maidana and removal,
we think in the interim is
people are worried about their exposureto this compound.
I think a fridge filter or something likethat is is a prudent strategy.
One of the things we're interestedalong with that is when we think
(18:23):
of activated carbonto remove compounds from water,
we typically think of a sorptiontype mechanism.
This product is likely a reactiontype mechanism, meaning that it's going
to react on the surface of these filtermaterials and produce other products.
And so we're interested not only inits removal but what products it forms.
(18:45):
It's likely that it might formsomething like nitrate.
We we actually showed thatin the science paper when we basically get
this compound with light under Fatalis,one of the products is nitrate.
And nitrate has its own host of healtheffects.
It's like it's going to form nitratein relatively low levels.
But we're interested
to see what these end productsare of the point of use filtering as well.
(19:08):
There's a lot to be learned there,but I think
because there's a lot of evidenceto suggest that a whole water
filter will be effectiveat removing the compound.
Generally, in the United States,
we're blessed to have very high qualitydrinking water,
and I don't want this studythat reveals this new byproduct
to drive more people away from their tap.
(19:30):
Now that being
stated, I think we have a responsibility
to run this, to grow and figure outits toxic logical relevance.
And we'll report that in a responsibleand timely way.
But in the meantime, if you're concernedabout some of these disinfection
byproducts than the beginnerdrinking water point of use filter,
a fridge filter, or something like thatI think can mitigate exposure.
(19:53):
No reason to go away from Britadrinking water.
Our drinkingwater systems are marvels in this country.
I know people like to saythe infrastructure is old,
and that is truein many cases that there is need
for revitalizationin more research in those types of areas.
But it's not to say that our drinkingwater is anything but safe.
(20:14):
You know,we're really blessed in this country
to deal with these types of problemsof disinfection byproducts
as opposed to like getting sick or even,you know, dying from unsafe water.
Water that's not disinfected.
Maybe just stand with thatnote of perspective.
It's something that I like to remind
both myself and my students as we're doingthis work, that the compounds
that we're looking at right noware things that can lead to disease
(20:38):
in time frame of decades, thingsthat we use disinfectants for.
They protect us from being sick todayand tomorrow.
And so we always need to keep that in mindand in the area that I work in.
Special thanks to Julian Fairey.
For the Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
(21:00):
Please subscribe wherever you get podcastsand if you like
our program, share with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
The United States
has benefited from centuriesof improvements in drinking water safety.
And most Americans can trustthat clean water comes from their taps.
But contaminants can come into systemsfrom harmful bacteria
leaching of lead, copper and microplasticparticles from plumbing hardware,
(00:26):
or even human error.
When a clean water line is accidentallyconnected to a contaminated one,
we are joined by Julian Fairey, associateprofessor in the Department of Civil
Engineering at the University of Arkansas,whose research group focuses on drinking
water treatment and understandingthe natural organic matter
and disinfection byproducts that resultfrom water treatment processes.
(00:46):
Professor Fairey,thank you for joining me today.
Pleasure to be here.
Thinking about the water systema little bit as we ease into it.
Can you talk about the general structureat all, like for people
that don't know anythingabout how it works?
Are these broken down by region or cities?
Certainly both. In some cases.
Most certainly big cities have multipledrinking water treatment plants.
(01:08):
Some regions that are more ruralregions will have sort of centralized
drinking water treatment plantthat supplies a fairly vast area.
How I think of drinking water treatmentbeing broken down
is by groundwater or surface water.
Groundwater treatmentis typically a little bit more simple.
We think of, you know, kind of well water.
If you grew up in the countryas being fairly high
(01:32):
quality water,not a lot of particles in it.
And so the treatment can be quite minimalin that regard.
And, you know, there's many cities.
Houston, for example, usesa lot of groundwater wells.
They blend that with surfacewater sources.
And when you do that surfacewater in general, I mean,
they're they're exposed to the atmospherearound to different elements.
And that's where we think of a little bitmore advanced treatment
(01:54):
being absolutely necessaryin order to protect human health.
So how do we treat water?
Well, reallywe want to get the stuff out of it.
And so if you hold up a water glass, it'sgot things floating around in them.
You're not going to have a sensethat's safe
and that's a good instinct to adhere to.
And so we want to get particles out of it.
And we want to stabilize itfrom a microbiological standpoint as well.
(02:18):
And so really what that requiresis making these particles
when they come into a water
treatment plant from like a river sourceor a lake source, for example.
The particles are generally pretty small.
And so what we typically do is we addcoagulant and mix at a relatively gentle
rate in order to make bigger particlesform that subsequently settle.
(02:40):
And we can filter out.
In addition, we add chemical disinfectantsto kill bacteria,
inactivate microorganisms,and when we send us the water
through a series of pipes that we refer toas the distribution system
that enters all our homes.
And so we can basically drinkclean water on demand.
What kind of chemicals are we using inthe process to disinfect drinking water?
(03:02):
There are a number of chemicalsused in in the United States.
We break those chemicals into whatwe refer to as primary disinfectants.
So disinfectants are used in the drinkingwater treatment plant
and then secondarydisinfectants, chemicals
that are used within the drinkingwater distribution system.
And so these chemicals can be very similar
or a little bit different between primaryand secondary disinfection.
(03:24):
The most common disinfectant used in theUnited States and worldwide is chlorine.
People in my companyusually refer to this as free chlorine,
because we distinguish free chlorinefrom the second
most common type of disinfectant,which are chloramines.
They're often referredto as combined chlorine.
Some chloramines are created by reactions
(03:45):
between free chlorine and ammonia.
And so most drinkingwater systems in the United States
use free chlorineas a primary disinfectant.
The majority of water systems also usefree chlorine as a secondary disinfectant.
But about one third of water systemsin the United States
use chloraminesas a secondary disinfectant.
(04:08):
And so, let's say between free chlorine
and chloramines, those make up the bulkof our drinking water.
Disinfection in the United States.
There are utilities that use other,certainly primary, disinfectants.
Ozone is a fairly common one.
Chlorine dioxide is somethingthat's used in many places
around the United States, includingwhere I live in Fayetteville, Arkansas.
(04:30):
But in terms of drinking water,disinfectants in the distribution system,
secondary disinfectantsis or typically free chlorine chloramines.
And there may be a small handfulof systems that use chlorine dioxide.
So all of these processes have byproducts.
And I understand that's quite a bitof what you've studied over the years.
Can you talk a little bit aboutsome of these byproducts that result?
(04:52):
Sure.
And so all these disinfectants,they inactivate, microorganisms,
which is their primary purpose,but they're also oxidants,
and they react with naturally occurringorganic materials
that are naturally presentin drinking water.
Some of these reactions resultin the formation of unintended compounds
(05:13):
that we just generically referto as disinfection byproducts.
This was first realized,and I would say the mid 1970s, where
there were some studies doneto show that free chlorine,
if you just add it to a drinking water,reacts with this organic matter
that's naturally present in the drinkingwater systems, and it forms a compound
(05:34):
called chloroform, chloroformas part of a group of trial methods.
And so it was realized in the earlyor in the mid 1970s
that these unintended compoundsformed subsequently,
through toxicity testsand things like this, we realized, okay,
we need to regulate these groupsof of disinfection byproducts that formed.
(05:56):
And so you see, in the mid 1990s,we regulated tri, our methane,
and another group of disinfectionbyproducts called our cedar gas.
It's in these are two groupsof disinfection byproducts that on a mass
basis form at the highest concentrationsin chlorine, emanated waters.
In the last 50 years, we found,
(06:17):
you know, 6 to 700 disinfection byproducts
forming out of all sortsof combinations of disinfectant regimes,
natural organic matter types,as well as like different
background ions that are in waterlike bromide and chloride.
That's one group of disinfectionbyproducts.
The other group that I've been moreinterested lately are products that form
(06:40):
from the disinfectant alone,so they don't need natural organic matter
or anything other than the disinfectant.
We've long known when chlorine dioxide,for example, decomposes, it
forms chloride.
And this is regulatedin our drinking water systems.
But there's been this mystery compoundassociated with chloramines that we know
that's formed.
(07:01):
We've known this since 1980,but we haven't been able to identify.
And that's what my work in the lastten years has been about, trying to go
about identifying this compoundthat is a natural decomposition product.
Of Corning disinfection.
So can you talk about thatchlorine nitride anion.
Why was that of interest or a mystery?
(07:21):
The story starts back in 1980.
There was a PhD thesis out of Cal Berkeleythat showed when we're monitoring
the two principal disinfectant compounds
in chloramine systems,monoclonal amine and dichloromethane.
There was two methods at the timeto determine their concentrations,
and initially
these two methods were giving the sameresult for multiple mean and dichotomy.
(07:44):
But over time these two methodsdiverted from one another.
One of the methodswas based on new absorbance,
and so whatthey were able to determine was,
as chloramines are breaking down,
they're forming this compound that createsan ultraviolet interference
with one of these methodsthat they were using.
(08:04):
And so they knew this unknown compoundwas forming that subsequently
became known to people in my fieldas the unidentified product
was a stable productthat formed during quorum decomposition.
And it was just a mystery of whatthis thing, one was.
A lot of work done in the 1980sand 90s, primarily by Rich Valentine
(08:27):
out of University of Iowa,that was aimed at trying to identify
this mystery compound,and they did a lot of really innovative
work in chloramine chemistry,and that's the work we built on.
And so they developed methods to form
this compoundat relatively high concentrations.
(08:47):
When you want to try to identifysomething,
that's one really effective strategyfor going about that, transform
this thing at very high concentrations,see if we can get some other
analytical techniques to it.
And so they formed this mystery compoundthat they weren't able
to determine its molecular formulaor its structure.
But they were able to break it down
(09:12):
and showedthat contained chlorine and nitrogen.
So that was a hint.
They also showed that materialsthat are in point of use filters,
like a Brita filter, for example,was able to destroy this compound.
And so that was a useful insighton the treatment side of things
that people don'twant to be exposed to this compound,
(09:32):
perhaps a home water filterwould be effective in removing it,
but they ultimately weren't ableto identify this compound.
And so when I got into chloraminechemistry
work, I was I was basically a PhD studentat the University of Texas at Austin,
and I was looking at how Chloraminesreacted with activated carbon.
(09:53):
It was for a completely different process
unrelated to this mystery compound,but it got me into chlorine chemistry.
And subsequently, when I startedmy faculty job here at the University
of Arkansas,I was looking for a fundamental way
to explain the formationof a group of disinfection
byproducts and chloramine systemsthat are called nitrosamine.
(10:14):
Together with a colleague of mine,a friend from graduate school,
his name is Dave Warmand he works at USP in Cincinnati.
We set about trying to explain hownitrosamines formed in chloramine systems.
So I got a grant funded by theNational Science Foundation back in 2020
to kind of better explainhow nitrosamines form in Corning systems.
(10:35):
And what we showed waswhen chloramine means
decompose,they form reactive nitrogen species.
And this was a big leap forwardin the science of causing decomposition,
really filled in a major gapfrom the original work done
by Valentine and his colleaguesback in the 1980s and 90s.
So what we showed specifically waswhen chloramines decompose under drinking
(11:00):
water conditions,McCormick decomposes to dichotomy,
and then dichotomy undergoes hydrolysis,just meaning it reacts with water
to form nitro oxo and my Troxellis this really interesting
reactive nitrogen speciesthat has a number of functions, both like
physiology, but also in, as it turns out,in our chloramine systems.
(11:23):
And what we showed was my outsole reactswith dissolved oxygen,
which is present in all our watersjust naturally, and forms another
reactive nitrogen species called pyroxenenitrate.
And proxy nitrate, as it turns out, decaysrapidly to things that we
are really familiar with in drinking watertreatment nitrate in nitrate.
But along the way, it forms a whole hostof reactive oxygen and nitrogen species.
(11:47):
And turns out some of these specieswere key in the formation of NDma.
These nitrosamine.
We also realized in this work
that proxy nitrate decomposition products
were involvedin the formation of this mystery compound.
So we did some studies under both
(12:07):
low and ambientdissolved oxygen conditions
that showed this mystery compoundwas mitigated under low D.O.
conditions, meaning that proxy nitrateor its decomposition
productswas likely involved in its formation.
So this kind of brought us back to seekingto identify this mystery compound now.
And so, as you may get a sense, thisthe chemistry of this system
(12:31):
is starting to get pretty complicated.
And this happened to coincidewith my sabbatical
year here at the University of Arkansas.
And I was like,I need to solve this problem.
And so where could I go to do this?
One of the reviewers or so on one of our
NMA papers was Chris McNeil.
He is a professor at Zurich,and he had reached out just sort of
(12:55):
with a congratulatory message regardingone of our papers after it published.
Very nice.
And this kind of
started up a conversation of, hey,can I come over there and do a sabbatical?
Or maybe look at this problemof this mystery product.
He's more of a trained chemistand I'm more of an environmental engineer.
And so this worked out. It was great.
But I went over there and spent a yearin Switzerland
(13:19):
trying to identifythis, this mystery compound.
And Chris had a an analytical chemistin his group in doing this
sort of it's who is a postdocstill is a postdoc in his group,
and she just has really stronganalytical skills.
And so we set out trying to identifythis compound with some of the equipment
(13:41):
over in Switzerland and Chris's laband in a neighboring lab called AVL.
And that's really where the story startedgetting interesting
in terms of having some successin identifying this compound.
So now that you kind of know what it is,
what becomes the next steps into like,I don't think you know that much
(14:01):
about how toxic it isor what its impacts are on people,
like, what are kind of the next stepsthere with that research?
So as we speak, I have a
PhD student in my lab trying to producevery high quantities of chlorine.
Nature might I anion for toxicity testing,
we needed to producevery high concentrations
of this compoundfor some of the spectroscopy work
(14:22):
that went into the identificationof the chemical structure by NMR and Ftir.
But we need even larger quantitiesfor toxicity testing.
And so we're trying to scale upthose methods now
both in terms of producing this compoundbut also purifying it.
We want to make sure that it'sonly this compound in toxic retests.
(14:43):
And so I'm not a toxicologist,but I'm collaborating with colleagues
at USDA as well as in Switzerland
and in other labs in order to assessthe toxicity of this compound.
So that's one major effort that'songoing of press we're interested in.
Hey, how toxic is this thing?
What what does this mean for us?
And I think that'sa very important question to answer.
(15:06):
The other thingthat was interesting for us
was so as partof the publication in science,
we sampled ten water systemsfrom across the United States.
So these were systemsthat all use chloramine disinfectants.
And so we found this compound called my.
And I'm in all system.
There was 40 total samples.
We found it in all 40 samples.
(15:27):
But we found it at really a sort of a vastrange of concentrations,
which was somewhat unexpected.
All the way from like one microgramper liter up
to 120 micrograms per liter.
And so since chlorination right at nineis the decomposition product of cornyn's,
requirements are all added at aboutthe same amount in our water systems.
(15:49):
We were a little bit puzzledas to why there was such a large range
of concentrations.
And so what I'm doingis trying to explain that
there must be some propertiesof these water systems,
some other chemistrieswithin the water that maybe quench some
of the intermediates that are involvedin the formation of this compound
(16:11):
or enhance its formation in some way.
We think it's relatively stable.
Once it forms, we don't thinkit's going to decompose a lot.
But what are the sort of the keywater chemistry parameters
that lead to relatively lowformation versus high formation?
Regulated disinfectionbyproducts have standards at trial,
(16:32):
and these things are regulated at a masksome of 80 micrograms per liter.
How low acetic acidor at 60 micrograms per liter.
So we're finding,
you know, core nature might anionbetween 1 and 120 micrograms per liter.
And so if this proves out to be toxic,logically relevant, likely there'll be
some threshold at which it'll be toxic and
(16:54):
is that level 500 micrograms per liter?
Is it at 100 micrograms per liter?
Is it at 50 micrograms per year?
We don't know.
But right nowwe're interested in understanding.
Well, why are some systems formingrelatively low concentrations.
Why are others formingrelatively high concentrations?
You know, if it turns out thatthis is toxic, logically relevant?
(17:15):
Well,if we understand how it's forming better,
we can then, you know, advisechloramine systems.
Okay.
You know, if you want to controlthis product, here's what you do.
And that's kind of the workthat is ongoing now
along with the toxicity testing.
And you said something as simple as a pumpwater filter can remove it
from that water system.
What was shown by Rich Valentine and hiscolleagues is back in the 1980s and 90s,
(17:39):
when we still refer to this compoundas the unidentified product.
He showed that the unidentified productcan be removed by activated carbon,
which is a materialthat's in point of use filters,
typically in a fridge or pitcher filterthat could be in your house.
We haven't validated that yetwith chlorination might A9 specifically.
So we think that should work.
(18:00):
There's testing that's about to startat a US EPA in Cincinnati in this regard.
Evaluating point of use filtersfor chlorination Maidana and removal,
we think in the interim is
people are worried about their exposureto this compound.
I think a fridge filter or something likethat is is a prudent strategy.
One of the things we're interestedalong with that is when we think
(18:23):
of activated carbonto remove compounds from water,
we typically think of a sorptiontype mechanism.
This product is likely a reactiontype mechanism, meaning that it's going
to react on the surface of these filtermaterials and produce other products.
And so we're interested not only inits removal but what products it forms.
(18:45):
It's likely that it might formsomething like nitrate.
We we actually showed thatin the science paper when we basically get
this compound with light under Fatalis,one of the products is nitrate.
And nitrate has its own host of healtheffects.
It's like it's going to form nitratein relatively low levels.
But we're interested
to see what these end productsare of the point of use filtering as well.
(19:08):
There's a lot to be learned there,but I think
because there's a lot of evidenceto suggest that a whole water
filter will be effectiveat removing the compound.
Generally, in the United States,
we're blessed to have very high qualitydrinking water,
and I don't want this studythat reveals this new byproduct
to drive more people away from their tap.
(19:30):
Now that being
stated, I think we have a responsibility
to run this, to grow and figure outits toxic logical relevance.
And we'll report that in a responsibleand timely way.
But in the meantime, if you're concernedabout some of these disinfection
byproducts than the beginnerdrinking water point of use filter,
a fridge filter, or something like thatI think can mitigate exposure.
(19:53):
No reason to go away from Britadrinking water.
Our drinkingwater systems are marvels in this country.
I know people like to saythe infrastructure is old,
and that is truein many cases that there is need
for revitalizationin more research in those types of areas.
But it's not to say that our drinkingwater is anything but safe.
(20:14):
You know,we're really blessed in this country
to deal with these types of problemsof disinfection byproducts
as opposed to like getting sick or even,you know, dying from unsafe water.
Water that's not disinfected.
Maybe just stand with thatnote of perspective.
It's something that I like to remind
both myself and my students as we're doingthis work, that the compounds
that we're looking at right noware things that can lead to disease
(20:38):
in time frame of decades, thingsthat we use disinfectants for.
They protect us from being sick todayand tomorrow.
And so we always need to keep that in mindand in the area that I work in.
Special thanks to Julian Fairey.
For the Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
(21:00):
Please subscribe wherever you get podcastsand if you like
our program, share with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
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