PAHs and coal tar—old contaminants with emerging concerns

PAHs and coal tar—old contaminants with emerging concerns


It’s really a privilege to be here
to speak with you this morning. You may be wondering why is it that at a
conference about emerging contaminants, we’re having a presentation
about PAHs and coal-tar. Given that we have known for a very
long time that these are contaminants. In fact, in the case of coal-tar,
we’ve known for centuries. It was way back in 1775
when Sir Percival Potts, determined for the first time that
environmental exposure could result in cancer. This was for young boys, for
chimney sweeps in London, who had, increased incidences of scrotal
cancer because of their contact, with the coal soot that
was lining the chimneys. More recently, but almost a hundred years ago, the first relation, the first
understanding that an individual, chemical could cause cancer was in
1933 when it was determined that, Benzo[a]pyrene, which is a polycyclic aromatic
hydrocarbon or PAH could cause cancer. That was the first incident of that. Since then, numerous coking facilities,
diet plants, manufactured gas plants, and other facilities that have
produced coal-tar as a waste, have been named as Superfund sites. There’s been quite a bit of
research on coal-tar and PAHs, and environmental and human
health effects since then. So in a way, like Stephanie
was talking about yesterday, we might consider that these
are legacy contaminants. But today I want to focus on continued
use of coal-tar in our communities, and what we’ve learned very recently,
much of the research has been done, in just the last 5 or 10 years,
about environmental effects. I work for the US Geological Survey. This is the environmental research arm, the earth science research arm
for the federal government. The USGS is not a regulatory agency. We don’t advocate for any regulations. We don’t make recommendations
for public policy. But it is part of our mission to do policy
relevant science and to communicate that, science to other agencies, to the public,
and to the academic community. It’s in that capacity that I’ve
been invited here today. As part of the USGS, there’s a program called
the National Water Quality Assessment Program, or the NAWQA program. One of the main objectives of that program
is to identify trends in water quality. Are concentrations of
contaminants getting better? Are they getting higher? Are concentrations decreasing? If possible, can we determine why? The research group that I was working with
at that time about 10-15 years ago, was looking at a particular
aspect of trends. That’s trends in contaminants that
are associated with sediment. Things like Chlordane, DDT, and Lead. The approach that we were using was to collect
sediment cores from lakes and reservoirs, and use those as archives of water
quality or of sediment quality. By looking back in time down the cores
and then looking up to the surface, we can see our concentrations of
contaminants increasing or decreasing. We saw some good news
stories not entirely unexpected. We saw that concentrations of DDT in sediments
were decreasing across the country. Concentrations of PCBs,
concentrations of Lead, and some of the other heavy metals were
decreasing in lake sediment cores. But a surprise to us at least was, that concentrations of
PAHs were increasing. The reason, this was a surprise,
was that in the ’70s and ’80s, there were a number of papers that came out
that indicated the concentrations of PAHs, in sediment cores in remote
lakes were decreasing. Well that’s because remote lakes, most of
their PAHs are coming from atmospheric deposition. We’ve seen decreases in PAHs in the
atmosphere is because of the Clean Air Act, because of improvements
in home heating, and because of use of catalytic
converters in vehicles. Why then were we seeing
increase in concentrations? Well one big difference is that, we were collecting many of our
sediment cores from urban lakes. In urban lakes, much of the contamination
is coming in from storm water, rather than atmospheric deposition. That was an indication to us that we
needed to look for a source of PAHs, that was coming associated largely
with urban environments, or at least where people are and then
it might be associated with storm water. I want to digress here for just a moment, and just talk a bit about what PAHs are. They’re a very large group of contaminants. What they all have in common is
they’re based on the Benzene ring. Now benzene itself is not a PAH. It is a six-sided planar molecule:
six carbons with six hydrogen’s attached. But you can organize benzene rings in
different geometric configurations with, different numbers of rings and
every one of those is a PAH. Here’s just a few examples,
but as you can imagine, there are a lot of different configurations
that you could come up with. To make things more complex, we can
substitute a carbon atom with a nitrogen, or a sulfur or an oxygen, or we can substitute
a hydrogen atom with a double-bonded oxygen, a Hydroxyl group or a nitro group, and
every one of these is now, a different compound that’s a
PAH related compound. We know seven different
PAHs have been designated, by the EPA as probable
human carcinogens. We know also that PAHs are ubiquitous,
particularly in the urban environment, because they’re formed whenever we heat
or combust anything that contains carbon. Anything like used motor oil, atmospheric
industrial emissions, and also products that involve the heating
or combustion of carbon like tires. These all contain PAHs. It’s been historically a challenge
for environmental sciences to determine, which of these sources might be the most
important in contributing PAHs to the environment. Well a first clue came not from our big
national study, but it actually came from work, that was being done by the City of
Austin Department of Watershed Protection, which is a cooperator with the
USGS in the state of Texas. In the early 2000s, they had a project
where they were measuring, collecting sediments from small streams
actually small tributaries and even, drainages across the city and analyzing
those for a large suite of compounds. These neighborhoods where the
sediments were being collected, these were not heavy industrial
or even inner-city neighborhoods. These were the types of neighborhoods
where we live and work. They were single-family, multi-family
residential like commercial areas. In some of these drainages, they measured PAH
concentrations above 1,000 parts per million. To put this into context: The concentration above
which we would expect to see, adverse effects on benthic biota is 23. Concentrations above 1,000
are on the level of what, we’d expect to see at in
the soils of Superfund sites. This was a very high concentration. A very astute member of their research
team decided to walk upstream. When he walked upstream, he just saw
some apartment complexes with parking lots. He thought at first,
well maybe it’s asphalt. But asphalt actually has relatively
low concentrations of PAHs. He took a harder look at the asphalt, and he realized that it was
coated with a black material. That black material is a very
common product used called, ‘Pavement Sealcoat.’ You’ve all seen this. In fact, if you parked in the parking
lot here, you’ve walked across it. Sealcoat is a product that is sprayed or
painted on the asphalt pavement, of parking lots, of some
playgrounds, of driveways. It’s marketed as improving the
appearance of the parking lot, and of increasing the longevity
of the underlying asphalt. It’s very rarely used on public roads. It comes in two essential
formulations in the U.S. Dominantly these two: There’s an asphalt based
product, which is mostly used, in the western United States,
west of the Continental Divide. And there’s a coal-tar based product, which is dominantly used
east of the Continental Divide, These two products look very similar. They’re marketed similarly. They’re applied similarly. But chemically, they’re very different. Asphalt and coal-tar are
very different compounds. Coal-tar is present in these products
at anywhere from 20 – 35% by weight. Essentially in a five-gallon bucket, about
1/3 of that is coal-tar or coal-tar pitch. Coal-tar pitch is, well, let me back up. Coal-tar is a residue that remains after
the coking of coal for the steal industry. Coal-tar pitch is achieved by
taking coal-tar and distilling it. During the distillation process, the
lighter-weight chemicals are removed. They have commercial value. What remains at the end of
that process is coal-tar pitch. Coal-tar and coal-tar pitch are
both known human carcinogens. They contain very high concentrations of
polycyclic aromatic hydrocarbons. To try and get a handle on what
might be some of the most, important sources of PAHs in the urban
environment, one of the first places that, we can look is simply at source
strength at concentrations. In parts-per-million, here’s those
compilations of PAHs pH concentrations. You can see that asphalt does indeed have
relatively low concentrations of PAHs. Motor oil is kind of interesting
because fresh motor oil, when it’s still sort of
clear and amber colored, when you first put it in your car,
it has low concentrations of PAHs. But as our car engines heated up
and it circulates through the car, for thousands of miles and it
becomes black, it then has, high concentrations of PAHs that have
been formed during that heating process. If we look at our two different
types of pavement sealcoat, the asphalt based product typically has
on the order of 50 parts per million. Similar to what we might
find in tire particles. The coal-tar based product
have on average about 70,000. Some products as low as 35,000. Some over 200,000 parts per million. At least on a concentration basis this is
potentially very potent source of PAHs. To put it into context, one gallon of
off-the-shelf coal-tar based sealcoat, has about the same amount of PAHs
as one gallon of used motor oil. In addition to high concentrations
another question we might ask is, “Well, how prevalent is its use?” From what we understand from
information provided by the industry, about 85 million gallons of coal-tar based
sealcoat are applied in the US every year. Which is enough to cover
about 170 square miles. Now I say every year because it’s
important to realize that sealcoat, must be reapplied
because it wears off. When it’s first applied it does indeed
make the pavement look black. It makes it look like new. But the abrasive action of car tires, and in this part of the
country of snowplows, abrades that dried sealcoat
into very small particles, which can then be washed off by
stormwater, can be blown off by wind. In fact if you go out to
a sealcoated surface, and you simply sweep up some
of the dust on the parking lot, you’ll find that there are lots
of little tiny dried black bits. Those little black bits are the
pieces of eroded sealcoat. We did that during some of
our lake coring studies, when we were in different
parts of the United States. We swept up dust from parking
lots across the watersheds. We had the PAH concentrations
measured at our national lab. This anecdotal information
that we’d heard, about the use of the low PAH
asphalt product in the West and the high, PAH coal-tar product in the East seemed
to be borne out by the concentrations, that we were measuring in the dust which
was similar to what the City of Austin, had measured in some of
those drainage sediments. Now we also measured PAHs on unsealed
parking lots in the same watersheds. We got very different results. The thing to remember here is that these
parking lots are in the same watersheds. The only difference is that
they’re not sealed. They still have these other urban
sources of PAHs, dripping motor oil, automobile exhaust, atmospheric
deposition, tire particles. The only difference is the presence
or absence of sealcoat. Now once the sealcoat wears off, there
are a lot of different places that it can go. It can wash off, as I mentioned in
stormwater, it can be blown off by wind, onto adjacent areas, paved areas or
turfs, it can stick to tires and be, tracked off onto other surfaces, it can
stick to the bottom of your shoes and be, tracked into your home and become
incorporated in the house dust. The lighter molecular weight PAHs are volatile
and they are released into the atmosphere. Each of these different pathways has been
the subject of a couple of studies. But today what I want to focus on
because this is a conference, on emerging contaminants in
the aquatic environment is: I want to focus on the question of runoff. Now it came to light in about well
about seven years ago now. This was recorded by the Boone County
river keepers, they put a video up on YouTube. They were concerned because a bank
had sealcoated a parking lot. That night it had rained. All the fish for a mile and a half down
stream were dead the next morning. In response to that, the pavement
coatings technology counselor, the PCTC which is the trade group who
represents the coal-tar sealcoat industry, they issued some best management practices. They stated that coal-tar
sealcoat should not be, applied before the sealant has had time
to cure which is typically 24 to 48 hours. But they stated that after that
curing time that there was, “Zero to negligible risk
to the environment.” They also stated that, “These fish had not been poisoned.” That in fact they had died because their
gills had been glued shut by the sealcoat. They had asphyxiated. This gave us two working hypotheses
that we wanted to test. We had a test plot sealcoated with coal-tar
based sealcoat by a professional applicator. We collected the runoff. We had some toxicity tests done at the USGS
Columbia Environmental Research Center. I don’t know, some of you here
may know Chris Ingersoll. He was the lead
toxicologist at that time. We used two test species: Ceriodaphnia dubia. Well affectionately known as the water
flea which is an invertebrate, that lives in the water column. Newborn head minnows,
or Pimephales promelas. We tested both the undiluted runoff, and runoff that had been diluted
1-10, so just a 10% solution. The organisms were exposed for 48 hours. At that time they were then
removed to clean water, and observed for another 48 hours. During that 48 hour recovery time,
half of the organisms were exposed, to four hours of UV light to
simulate exposure to sunlight. Now the reason we did this is that PAHs,
or some PAHs, are photo toxic. What that means is that these PAHs
can absorb energy from sunlight. When they release that energy, if the PAHs
have been absorbed into tissues, when they release that
energy it creates reactive oxygen, species which can destroy
cells and damage DNA. Many PAH issues have been shown to have
their toxicities increase by, tens, hundreds, or even a thousand
times with exposure to sunlight. Let’s look at some results. We’re going to be looking at
results, for the sake of time, at we’re going to focus on
the Ceriodaphnia dubia. Here’s our control. This is exposure to run off from
unsealed asphalt pavement. We saw about 10% toxicity, one
organism in ten, whether or not, the individuals, the organisms
were exposed to UV light. We’re going to use this as a control. We’re going to say that anything
over 20% mortality is toxic, because of the presence of the chemicals from
the runoff in the coal-tar based sealcoat. Taking a look at those results: First we’re going to look at the
results before UV exposure. There’s a lot on this graph
so I’ll walk you through it. The yellow bars are the undiluted sealcoat
and the turquoise bars are the 1-10 dilution. Along the x-axis, you’re looking at
when the sample was collected. Starting just a few hours
after sealcoat application. Our last sample was collected
111 days after application, or a little bit more than 3 months. Then along the y-axis is mortality. You can see our toxic
threshold there at 20%. If the bar goes all the way up to the
top, then we have 100% toxicity. Everything died. What we’re seeing is that for the undiluted
runoff we’re continuing to see toxic, effects out to more than a month
after the sealcoat was applied. However for the 1 to 10 dilution,
we’re not seeing any toxicity. Then organisms were exposed to
the UV light and at that point, we saw 100% toxicity across the board. Everything died regardless of the dilution. Regardless of how long after sealcoat
application the test had been done. This addressed the first
hypothesis which is that: 48 hours is not necessarily the
amount of time after which, the runoff does not present
a risk to the environment. Also, we saw no evidence of sealcoat
covering any of the organisms. The runoff that we collected was
tea colored it was essentially clear, but kind of the color of tea with a little
bit of black bits down at the bottom. There was no evidence that the
fish gills had been affected or that the, organisms had been affected by
the actual particles of the sealcoat. This addresses acute toxicity but there are
some other questions that arise such as, What about chronic effects
or less visible effects? We were acquainted with a
research consortium in France, that looked specifically at
the effects of PAHs on DNA. They were interested in our research. They asked us if we would send them
some samples to do some studies. They use a model cell line, which has been developed particularly to
look at the effects of PAHs on DNA. The types of DNA damage that they
addressed with this experiment here was, a combination of effects from DNA
strand breaks and alkylated bases. That’s that one on the right
with a little red dot there. What that is is when an alkyl
group attaches to a DNA base, and that can cause this
replication of the DNA. They used a type of test called a Comet
Assay which measures these two effects. They looked at both the 1 to 10
dilution like we looked at in the, previous study they also looked
at a 1 to 100 dilution, so just 1% runoff and 99% control water. In these graphs, we’re looking at the 10% dilution
on the top and the 1% dilution on the bottom. In the comet assay, the higher
the bar, the more the DNA damage. The bar on the far left is the control. Then the open bars are the cells
that had not been exposed to UV. The white bars are those that
had been exposed to UV, in conjunction with
exposure to the runoff. What we’re seeing there is that: With the UV exposure, we are
seeing significant DNA damage, in both the 1 to 10 and
the 1 to 100 dilution. They just tested samples out to 36 days
after the sealcoat application. We’re seeing here evidence of
the possibility of chronic effects, in addition to the acute toxicity. More recently, some similar research has
been done by collaboration between, researchers from NOAA
Washington State University, and the Fish & Wildlife Service. This work was first authored
by Jen McIntyre. Here we are looking at the effects of
exposure on juvenile Coho salmon. This is runoff that we’ve
collected just two hours. The minimum drying time after
the sealcoat was was applied. You can see these fish are
experiencing loss of equilibrium. Within 5 hours, all of the
individuals had died. Now here. This is sealcoat that was collected
207 days after application. So a little bit more than 6 months. The individuals are swimming
at the surface and doing gaping. This is not normal fish behavior. At the end of their exposure period,
55% of the individuals had died. This is another example of acute toxicity. They went one step farther. They also looked at sub-lethal
effects using zebrafish embryos. They exposed the embryos to the
runoff for 48 hours using the range of, concentrations from just after the sealcoat
was applied to more than six months, after sealcoat was applied and
they also looked at a number of, different dilutions down to 3%. We know that PAHs cause cardiotoxicity in
fish, toxicity through heart damage. This is primarily associated with the
tricyclic PAHs, or those with 3 rings, which include phenanthrene which is
present in very high concentrations in coal-tar. They did find cardiovascular
abnormalities including cranial, hemorrhaging and blood pooling,
pericardial edema, collection of fluid, around the heart which is shown
in that circled bar there. They also found reduction in
embryo length and eye size, which is shown with the
circled arrow on the left. They also measured some
molecular markers, that show that the DNA
is actually being affected. They were looking at ****
induction in the fish. They found this for most of the dilutions. They found this for all of the
samples all the way out to, more than six months after application. One very interesting thing
that they did find was, that if the runoff was filtered through
a bio-retention system it eliminated, all the visible effects of toxicity and it
greatly reduced the induction of the ***. This does suggest that there
might be some remediation approaches, that could be very effective for treating
runoff from these types of sealed surfaces. These last two studies that
we’ve talked about are, looking at runoff but remember earlier I
talked about the fact that the sealcoat, particles themselves are abradible,
they erode and they run off. What happens if those become incorporated
in stream or lake sediment? Does that have an effect on organisms? There have actually been a number of
studies that have investigated this. There have been a couple of studies that
have looked at individual species. A species of frog and a species of newt. They found that exposure to environmentally
relevant concentrations of PAHs in sealcoat; they actually took sealcoat and spiked the
sediment with it and exposed the organisms, this resulted in some problem
swimming, loss of equilibrium, difficulty in the individuals being
able to right themselves and some, reproductive effects and
some growth effects. At higher concentrations,
it could cause toxicity. There are some other
researchers that look more at, community effects, that looked at
abundance and richness of the ecological, community and also found effects at
environmentally relative concentrations. These studies have been trying to
reproduce what we see in the environment. But what about the environment itself? What happens if we go out and
we look at existing stream systems? Do we see any effects well? This was very thoroughly examined by a different
USGS research group located in Wisconsin. They did a study in Madison, which was
just published this year. They collected stream sediment samples
from 40 different sites in Milwaukee. Measured PAHs. They found that 68% of sediments
had PAH concentrations that, exceeded that concentration at which we
would expect to see adverse effects to, benthic biota; so they exceeded that
23 part per million threshold. They then took the sediments and
did toxicity tests with Hyalella Azteca. They found a very clear dose-response
relation between the concentrations of, PAHs shown there as the ratio to the
probable effects concentration on the, x-axis and the mobility of the Hyalella
azteca after they are exposed to UV. Again, we’re seeing this photo
toxicity effect associated with PAHs. Then they asked the question, “Well, where might these PAHs be coming from?” They took a very thorough
weight-of-evidence approach. They use pretty much every
diagnostic tool that I can think of, I’m sure that they could think of. They included looking at diagnostic
ratios of PAHs in different sources and, in the sediments they looked at profile
correlations, principal components, analysis, mass fractions analysis, land
use analysis, or source receptor modeling, They pretty much threw
every tool in the book at it. Each of these approaches individually pointed
to coal-tar sealcoat as a potential source. Coal-tar sealcoat was the only
source among all of these different, approaches that was
uniformly identified. Let’s take a look at
some of their results. This is called profile matching. What’s shown here are the profiles in red
of six different common urban PAH sources. What’s shown in black, which is the same on all of these six, is the average PAH profile
for the stream sediments. You can match these statistically, which they’ve done using
the chi-squared statistic. But I think even by eye we
can see that the best, match is for the stream
sediments and coal-tar dust. This is the average profile for dust
swept from coal-tar sealcoat parking lots. Another approach that they did was
to simply look at potential correlations, between PAH concentrations and different
types of land use and the strongest, correlation that they found was for the
percent of the watershed that was parking lot. They did not find a strong association
between urban land use or between streets and roads. The percent of the base in this parking
lot was the strongest correlation. They also used a source apportionment
model which is a statistical approach that says, Okay, given the PAH profiles
of known sources, what’s the statistically best
combination of those sorts of sources, that would match what
I see in a sediment? When they did that, they found
that coal-tar sealcoat, was potentially contributing the largest
amount of PAHs in the sediments. Each one of those bars there is a sediment
that was tested with this approach. Each of different colors represents
a different PAH source. The orange bars are the contribution, from coal-tar based sealcoat which was
estimated to be contributing about 3/4, of the PAHs among the samples. The results of this work were very
consistent with previous research, by a number of different groups using
a number of different approaches, that show that the particles
that are going down, down the storm drain from the parking lots
are indeed making their ways to streams and lakes, and being incorporated in the sediment. To summarize we found that coal-tar based
sealcoat does indeed contain, very high concentrations of PAHs
and related chemicals. It’s very widely used in many
parts of the United States. It wears off; so it is potentially potent source
of PAHs to the urban environment. We know that runoff from
coal-tar based sealcoat, is a source of both acute and chronic
potential acute and chronic toxicity to, aquatic organisms and that the sealcoat
particles themselves when incorporated, in sediment also present a potential
chronic and potentially acute toxicity, to aquatic organisms. I want to end with the thought
that a lot of people, have been involved in this research that
independent researchers from the, academic community, from state, local, and
federal government agencies these, independent researchers have come to
consistent conclusions about the use, about the chemical makeup of this product and
potential risks to the aquatic environment. It’s resulted in 30 articles
in peer-reviewed scientific, journals and about
a dozen different reports. If you are interested in learning more
about this, we do have a web page. You’re welcome to contact me or my colleague
Dr. Peter Van Metre either by email or by phone. Our publications are available at
the website as well as a, couple of different USGS fact sheets
that we’ve written; I do have a few hard, copies of the fact sheet here at the
meeting if you’d like to take one home, with you please feel free to contact me
during the break. [Applause]

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