ORDA Science Webinar: 101 Series - Passive Sampling Technologies
[Moderator Jo Ellen Hinck] Couple of announcements on upcoming webinars that may be of interest to you. In July we have a statistics presentation from Richie Erickson talking about moving beyond P values and NRD statistics. So, if you're using half detection limits and P values for your stats, they're going to show us some different ways. And then in September, we're going to have one of our solicitors talking about science and NRDA cases. When do you need more science data? When is enough, enough? And so that will be in September. And then
in October at a date to be determined, but it's looking towards the end of the month, we are going to have a presentation on how oil impacts bird migration. So, if you do not receive email announcements, you can contact Samantha Foster. Although she's out on leave right now, so we'll drop in the chat who you should contact, but you can certainly contact me and we can get you on that email distribution. And then just the disclaimer there at the bottom that the findings and conclusions that are in the webinar do not necessarily represent the views of the DOI NRDA Program, the Department, and so forth. So, the attorneys are happy
now with the disclaimer. And, I am going to now give a brief… I'm gonna quit sharing my screen and give an intro to Dave. And Dave, you can start sharing at your convenience. So, Doctor Alvarez is the Chief of the Environmental Chemistry branch at the USGS Columbia Environmental Research Center located in Columbia, Missouri. His
research focus is on the development of innovative methodologies for passive sampler design and complex mixture analysis of various environmental matrices for emerging and legacy contaminants. As the inventor of the polar organic chemical integrative sampler, or POCIS, and researcher on other types of passive sampling techniques, he is widely recognized as an expert in the field and frequently mentors’ researchers on the use of these samplers. And many of you may have actually talked with Dave or use some of these samplers on your case. I've seen them used a lot in terms of, ephemeral data collection when an event happens. And
so, I'm really thankful that Dave's taken the time to kind of give us an update on these methodologies. They've come a long way even in the past decade or so. And so, Dave I'll hand it over to you, but a quick fun fact about Dave is that he has spent the last thirteen years involved with recreational soccer with his two daughters. That last six of which he coached his youngest daughter's team. So hey, thanks for giving back on the parent front as well, Dave. So with that I'm gonna go on mute, Dave, make sure you're off of mute and you can get started. [Dr. Dave Alvarez] Alright, sounds good. It was kind of a sad day of reminiscing just
the two nights ago when I dropped off my coach’s bag back to the league and now that my youngest daughter is going to be going into high school my wife and I have been saying well we've been coming to this park for games for thirteen years and now that's over, we'll be going somewhere else. So yeah, time flies and with that you know time flies also with passive sampling and I'm going to give you a little bit of a history and kind of really start you off with some of the basics. I know some of you probably have used passive sampler. Some of you may be familiar. Some of you may be joining 'cause you're wondering what the heck are these things. I've heard people talk about so. With that, we'll go ahead and start going through some of this and again towards the end of this, I'm gonna kind of share some case studies. I just kind of show how the samples have been used in real, some real scenarios, a couple of which are, you know, some different cases, but. Want to get everybody
kinda at the same starting point at least so you have an understanding of what I'm talking about before we actually get into the examples. So what is the passive sampler? Simply, It's an Abiotic device that's used the sample chemicals from the environment. There's samplers that are designed for sampling almost any environmental medium, you know, air, water, sediments, surface waters, groundwaters, but typically when you see these in the literature, people are generally talking about sampling of water and or air. The devices are considered passive because they have little to no moving parts. They don't require power to function, and they sample over prolonged periods of time, which, depending on the type of sampler using, that could be anywhere from hours to months to possibly years. And an example, I'll show
later, Passive samplers can offer advantages over other types of traditional sampling techniques, as they allow for the concentration of trace, but potentially toxicologically relevant mixtures of chemicals over time. And the samplers function in nearly all environmental conditions, regardless of water quality. If you are trying to do some sort of a contaminant assessment where you're wanting to look and use organisms as your metric of exposure. You know some sites just may be so contaminated that you organisms are not going to survive there. Maybe the
conditions just aren't quite right to where you know they don't really want to live there, so it's hard to find the animals to collect the sample. Passive samplers just kind of do their thing and they don't really care what the water quality conditions are. Surface water is probably the primary application, although we do see quite a bit of work in groundwater and poor water and there is air sampling techniques that are rapidly growing.
Depending on type of sampler that you're using, passive samplers concentrate chemicals from large volumes of water, anywhere from tens to hundreds of liters, over that deployment period that they're exposed. Which results in increased sensitivity and lower detection limits that may be possible with the traditional sampling techniques such as going out and taking a grab sample of water. Results from a passive sampler, often expressed as the time-weighted average concentration of that chemical, which then can be related back to ecological risk assessments to help determine potential exposure. Passive samplers only dissolve chemicals, or passive samplers only sample chemicals from the dissolve phase.
Chemicals that are bound to suspended sediment colloidal material or what fourth will not be sampled. The dissolve phase therefore mimics an organisms’ exposure through respiration and direct absorption into the body. A popular advantage that since these samplers are deployed environment over prolonged durations, it increases the possibility of capturing episodic events such as a spill or storm water runoff event that may be missed if you're just doing a routine, you know instantaneous type of sampling such as grab sampling. This is especially
important when you're sampling in remote locations where getting to a site quickly to capture an event could be difficult. Although an episodic event may be captured by a passive sampler, remember the data is expressed as a time weighted average, so the maximum concentration of that chemical during the event or the timing of the event can't be determined. This figure is a bit complicated, but it shows the differences between sampling techniques and a potential for detecting the chemical. To kind of walk you through it a little bit looking across the X axis you see peaks which represent changes in a chemical concentration over time. The dashed line represents a potential method detection limit for the analytical measurement.
Depending on when a sample was taken, you may be at the maximum peak and I'm not sure if you can see my pointer, but the maximum peak here by this little arrow represented on the left. Or you may have come back a day later and you're that peak is already went downstream and now you're back to baseline conditions and where you would have missed it. Another technique that's used sometimes by doing multiple sampling or some sort of automated sampling. It's coming up with a composite where you're collecting multiple samples over a time period, combining those into one. In that case, you can see your sort of collecting
around these changes in concentration, which you know increases your chances of being able to measure it. With the passive sampler, again, you're sampling over this entire time period here, integrating across multiple advance represented by these peaks, and although again we don't know what those maximum concentrations were, you can see by that red line that time weighted average concentration is measured. So at least you have that likelihood that you've measured that event that occurred, and you can say a little bit of something about what's happening at that site. When you talk about passive samplers, at least as far as how they fundamentally work, they generally fall into two groups, either equilibrium samplers, or integrating samplers. And it all depends on where they fall on the uptake
curve that you see in the bottom right-hand corner. This curve is a typical first order uptake curve and as you can see, it starts off in a linear phase, which is your integrating phase and then it goes in approaches an equilibrium. Equilibrium samplers typically have shorter exposure times in the environment, and they have a very low capacity for accumulating chemicals, which is critical for them to reach equilibrium in a reasonable time frame. Data from equilibrium samplers typically represent the latter stages of deployment as they are constantly adjusting to the current conditions trying to maintain that equilibrium. Equilibrium samplers most often are used for groundwater, sediment, pore water, and air sampling. Although
I have seen some surface water applications. Common samplers that you may come across that tend to operate more as equilibrium samplers are the solid phase microextraction fibers, the SPME or the "speemee's", polymers on glass, and different types of diffusion samplers. Integrative samplers have a much higher capacity to accumulate chemicals over time, which results in being able to use them for much longer exposure periods. You know getting into weeks to months or longer. An integrated sampler can act as both an integrative and equilibrium sampler at the same time. For example, a chemical with a low optimal water partition coefficient,
or low KOW will reach equilibrium much faster than a chemical with the high log KOW. So, could be similar chemical classes will take pHs, for example, the you know there's some of these petroleum hydrocarbons. Something like naphthalene is going to reach equilibrium considerably faster than something like crycine due to the differences in their log KOW. While
the sampler is working in that integrating or that linear phase, the data is expressed as a time weighted average concentration. These types of samplers are most commonly used for surface water and also for air applications. Common samplers are the SPMD, the POCIS, Chemcatcher, polyethylene devices or silicone strips, and there's many others as well. Three of the
more commonly used passive samples for organic chemicals are the semi permeable membrane device or the SPMD, polyethylene devices, PDS, and the polar organic chemical integrated sampler (POCIS). The SPMD has been used globally since the early 1990's. It consists of the lay flat, low density polyethylene membrane tube that's filled with a neutral lipid which is triolein. It's a common triglyceride that's in most vertebrate organisms. The SPMD is designed to sample neutral hydrophobic organic chemicals, typically with log KOW's between three and nine. So, when we think about a lot of the organic chemicals that have been used over the decades and are the ones that tend to be regulated. Those typically fall in that KOW range in our sample by the SPMD PED's are similar to SPMD's in the types of chemicals sampled the difference is it does not contain the triolein. It's a very similar,
it's the same type of membrane polymer. It just doesn't have the lipid. When comparing the mechanisms and uptake, they operate the same way, but PED's will have a lower capacity for retaining chemicals over time because it doesn't have that extra lipid reservoir. Whereas the SPMD's and PED's sample the hydrophobic organic chemicals, the POCIS was designed to sample the hydrophilic organics. So, chemicals typically with log KOW's less than three, so there's more water-soluble things that we were missing with those other samplers.
The POCIS consists of two micropores, polyether sulfone membranes that envelopes the solid phase extraction resin that traps the chemicals. The composition of that resin can change depending on the application. Depending on the types of chemicals you're interested in sampling. But typically, Oasis HLB is used and that's one of the more common resins used in environmental sample processing anyways. There's been many types of chemicals measured in SPMD's, SPME's, and POCIS. The most common chemicals can be grouped into either those legacy or regulated chemicals and the current use chemicals, and you can kind of see here, you know, where those breakout. The legacy or regulated chemicals include your Polycyclic Aromatic Hydrocarbons, Polychlorinated biphenyl PCB's polybrominated diphenyl ether, flame retardants, the PBDE's, and your typical legacy chlorinated pesticides, such as DDT and chlordane 's. As well as Dioxins
and Furans. Current use chemicals tend to include pesticides currently in use, and a lot of chemicals that you would think upcoming from wastewater treatment plant effluent. So, pharmaceuticals, hormones, fragrances and of course now with the interest in P fast.
Not going to really go into the details of uptake much, but just to kind of give you a quick idea of what happens for the SPMD's and PED, looking at the figure on the left, chemicals partitioned into that membrane. It polyethylenes a non-porous membrane, which means there's no physical holes and you can see those little white ovals. What those are, are cavities that are formed in the polymer chains. And chemicals can move through those cavities to use to get into the lipid layer on the inside. Little bit different with the
POCIS, the POCIS uses a microporous membrane, so there are actual water filled pores. Point one Micron in diameter, and chemicals typically are going to move through those water filled pores inside the sampler to where they get trapped on that resin. And although you do get some chemicals that do tend to partition through the polymer matrix as well. The use of passive samplers for metals is an established practice. I personally have less experience with those. But there are options available, just not quite as many configurations of samplers
as what you see on the organic side. Most of the research with passive sampling for metals tends to revolve around the sampling of pore waters, but there has been work done with surface waters as well as atmospheric deposition studies. I'll go through a couple examples that sort of the main metal samplers here. The first one is a diffusive gradients
and thin films, or the DGT. This is a popular sampler for measuring metals and surface and pore waters. It is a commercially available sampler which is kind of leads to its popularity. The DGT's consists of filter membrane that protects a rate limiting diffusive gel and then underneath that a gel that's embedded with the key lighting resin. And that's where the metals get trapped, is where they enter the sampler. There is a configuration of the
DGT that's a sediment probe that you can see on the pictures on the right. And this allows to be able to measure profiles of medals at the sediment water interface as well as that by death within the sediment. A common sampler for measuring metals and pore water is the peeper. Peepers can come in different forms, but typically they consist of a reservoir containing deionized water, which is separated from the external water by a dialysis membrane. Using frames with multiple sampling cells such as the picture on the top right allows you to determine some sort of depth profiles and metals and contaminated sediments. Again,
uptake is based on that diffusion of metals across that membrane as they tend to try to reach equilibrium. The sampling efficiency in peepers is determined by the equilibrium time and the diffusion coefficient of that chemical, or that metal across that membrane. Another sampler is the stabilized liquid membrane device, or the SLMD, which was developed by USGS. This is a research tool to measure cationic metals and surface waters. More recent developments has been using this sampler to measure medals at the sediment water interface, and I'll show an example of that later in the presentation. This sampler is constructed of a lay flat polyethylene membrane, the same one that was in the SPND and the PED samplers, and I apologize for all the very similar acronyms here. But the difference is, is This sampler has a metal binding agent in it that forms a a liquid phase on the surface of the membrane so when metals get interact with that liquid phase, they become trapped. This phase is stable
around the samplers we deployed for several weeks and then stored for several months before processing analysis. At that point, it's a very simple acid extraction, and then they're ready for analysis by common methods. The last type of sampler I'll show you is focused on atmospheric deposition of ionic species. This is a samplers term that ion-exchange collectors that use a both cation and anion exchange resin beds to US sample and retain a variety of ionic species. These have been used in remote locations and Arctic over long exposure times like throughout the winter, to measure low concentrations of various species through deposition. There are many other types of passive samplers or measuring chemicals and air, both organics and inorganics. Much of this work has a foundation, and the industrial
and occupational health area where passive monitors are commonly used to determine exposure to human workers. You know, are they being exposed to solvents or whatnot? Substantial work has been done to adapt those technologies into environmental air samplers, there are actually some global networks that exist for monitoring, especially organic contaminants in the air, but, uh, that's I won't get into that in this presentation. So initially, passive samplers from environmental monitoring studies were developed as a surrogate for biotic sampling. Considering the inherent difficulties of capturing some abiota such as fish, and the work required to process and analyze those samples back in the lab, the passive samplers do offer some advantages. One is that the passive samplers don't move, so you're assured of collecting a sample representative additive specific location as opposed to a fish that you don't know how much in its region it's moving around. Issues of metabolism and excretion and chemicals are not really an issue with these types of samplers. However, depending on the chemical
and the type of sampler used, there can be degradation or release of some sample chemicals that occur and I'll touch on that on in the next few slides. There's no need to analyze multiple tissue to obtain the full picture exposure, you know we've all heard that, and we're aware that some chemicals you know, if I think of pharmaceuticals, an antidepressant is going to interact with the brain. Other chemicals will go to other organs. We've seen the same thing when we’re analyzing different tissues of for example, of fish. You know, understanding where in that body a chemical may end up is important to make sure you get an accurate analysis. However just remember that, again when working with passive samplers we're only sampling from the dissolved phase. Therefore, they cannot provide an assessment of exposure due to particle-sorbed chemicals which may occur through feeding. So, when
you're doing that organism to passive sampler comparison, you know there are some differences. Some of which you know we can see here in this slide and this is, admittedly, it's a busy chromatogram here, and you don't need to know anything about chemistry, but if you look at this chromatogram here in the black on the left, the top is the analysis of a muscle the bottoms analysis of an SPMD both from the same site where we're looking for chlorinated organics. What you can see from here is on the SPMD, in the first half of this picture there's a lot of peaks, all of which represent different chemicals. Because it's in the early part of this chromatogram they tend to represent the lower molecular weight, of those lighter chlorinated organics. You don't see as many of those in the muscle, which tells me that either there was a more rapid excretion of these chemicals, or maybe there was some metabolism in these chemicals by the muscle. The other thing that we see
is the muscle tends to have bigger piece in the second half of the chromatogram that we really don't see from the SPMD. Those are ones that are the heavier, the higher molecular weight chemicals that most likely were more acute, more associated with particulate matter that then was retained by the muscle that would not have been sampled by the SPMD. However, if you start looking in that sweet spot, or you have that log KOW kind of between three and six, three, and seven, that works really well for an SPMD, and that would be sort of the middle of this chromatogram you see things will start to be a little more similar, which you can look at the bar graph on the right, which is four representative chlorinated pesticides, and you can see that the relative abundances of the different pesticides, they're pretty much the same at least in these examples. This here's another example of where SPM dies in caged fish were collected and analyzed for PCBS out of this particular graph as a principal component analysis, and it shows that the clustering of fish and SPMB was in fairly good agreement, which indicates that there was the SPMD was a suitable surrogate for measuring PCB concentrations that would have ended up in this particular fish species.
Some passive samplers such as SPMD's have a lower elimination rate constant compared to biomonitoring organisms which can have a major effect on the retention of chemicals over time, especially those absorbed during episodic events. Again, we're looking at SPND's and this time clams at the top figure, and you can see for the pHs overtime. The clams had much lower concentrations of the different pH's that remained. Doing some modeling, looking at first order residence time for a typical pH, in this case flooring. You can see that in the lower figure that you'll have detectable levels of flooring left in that sand sampler of the SPMD over at least a two-month period you should be all still detect something.
As opposed to the oyster, where after about fifteen days pretty much all detectable levels of or at least you know, definitely after five days was below that action limit. And by about fifteen days yield levels were back down to baseline. So, if there was an episodic event, you do have a defined time before that event would have been lost in these types of samplers. So, we're all used to having a sample analyzed and getting a concentration of a chemical. Although that's informative, it doesn't tell us anything about if that
concentration is important. With increasing frequency, environmental health assessments are become a multidisciplinary bringing together experts from across the scientist to answer these broader questions. You know, answering that, "so what" question. On a smaller scale, we're seeing an increase in using results from chemical measurements to help inform biological observations. This is often in the form of some sort of testing of extracts using a variety of either invitro assays to identify effects on a specific biological endpoint, but then there's also envivo experiments where whole samples or extracts are either injected in organisms or exposed in some other way to determine the potential effects on a complex living Organism. So, using passive samplers in the field is relatively straightforward.
You put it out, secure it, you walk away. You come back after certain amount of time. Take it back to the lab. There's always things that are trickier, but for the most part, it's straightforward. However, passive samplers can be complicated. As far as understanding some of the different techniques that are important to improve the performance, understanding quality controls that should be using and how to work with the data afterwards. Depending
on the type of sampler used and the chemical of interest, environmental conditions such as flow or turbulence around the sampler temperature and or the buildup of biofilm on the sampling service can have a significant effect on the chemical’s uptake grade. These conditions can be highly variable over time, and it's almost impossible to predict how those variables are going to effect at any given point of time. Because of this, user of passive samplers have long recognizers and needs to account for the impact of the variables on uptake kinetics over time. This is accomplished by means of the performance reference compound or PRC approach, and for those of you that have used SPND's or passive samplers in your study, you may have heard of PRC's what a PRC is. Is this a chemical that's added to the sampler during construction. And what it does is, while deployed in the field, this chemical slowly dissipates from the sampler. By comparing the amount of PRC remaining in
the sampler after deployment to how much you started with, provides a correction factor that you then apply to your uptake models to provide site-specific adjustments which improves the accuracy of your time weighted average concentration estimates. Selection of PRC's is an important factor as first they need to not interfere with the chemicals that you are interested in analyzing. They need to not be present in the environment because again, you need to know how much was lost. A lot of times it's recommended to use multiple
PRCs to cover a range of fugacities, which is just the ability of that chemical to leave the sampler during deployment. And preferably you wanna pick PRC's that are compatible with your planned analytical method. We all have tight budgets and trying to pay for two analysis is not always feasible. So careful selection of your PRC chemicals needs to be considered.
Lastly, if you are gonna use extracts in these passive samplers with some sort of bioassay or bioindicator taste test, you should not use PRC's and the reason why is any remaining PRC left in that sampler will get extracted and then expose the test and the PRC's themselves may be toxic or bioactive. So you don't want to confound your results without the PRC approach, or worse, for samplers of isotropic exchange kinetics. Which simply is the uptake rate is approximately the same as the declaration or the loss rate is. You can see from this figure here the two curves you know they tend to marry each other. Simplest way to think about this is the sampler is like a two-way door. As you move through that door, your movement is impeded by the same barriers regardless of which direction you're going. The same
things with the passive sampler. As a chemical is trying to move in and out of that passive sampler, regardless of the direction it's going, it still has to deal with any turbulence of water at the surface and still has to move through that biofilm or fouling layer. It's the same regardless of direction. The PRC approach is not as straightforward though for all passive samplers. Those which use a solid absorbent as the chemical retention
mechanism, such as I talked about with the POCIS, chemcatchers, and there's a few others, that are being used because of that solid absorbent they don't follow this isotropic exchange kinetics. So the use of PRC's either doesn't work at all, or it's extremely limited to just a few cases. Another concern is with sunlight. Sensitive chemicals such as pH's, that can undergo photolysis even after they have been sampled inside the device. The polyethylene membrane used in SPMD's in PED's is transparent to UV radiation so that UV radiation can penetrate the membrane and degrade the pH's inside the sampler. This is a real problem in shallow, clear waters and if you're doing offshore studies to where maybe you have deeper water, but it's clear but you have a white sandy bottom, it's also a huge issue there because you get a lot of reflection of the UV rays off that sandy bottom right back up to your samplers. Commonly used protecting deployment canisters offer some shielding but really not very much, so there are different techniques that people can use to protect samplers from light. It's much easier to do and protect them in a lake than it is a stream or river.
Generally, what we do to help monitor for potential degradation is to add a photolysis marker to the sampler during construction much like a PRC. The one most commonly used is dibenz[a,h]anthracene-d14. The reason why this one is selected is because it is photosensitive, and it's such a big molecule that the only way you're going to see any loss is due to photodegradation. It will not leave the sampler like a typical PRC will at least, not over normal conditions. I mean that'd be very extreme conditions to see any loss. So, by monitoring loss of this photolysis marker, you can have at least an idea whether or not other pH's is may have photolyzed or if there was any issues during your deployment. As with any
environmental sampling program, appropriate quality controls are essential to ensuring the reliability of results. Some passive samplers, especially SPND's and PED's, can readily sample error. Therefore, it's important include both lab and field blanks to distinguish concentrations and chemicals from the field from potential background levels. It is important to remember, that no amount of precaution can remove all traces of background contamination, which is why having blanks to account for any potential background is critically important. It's also
important include some sort of analyte recovery spike to determine the recovery of chemicals during the processing set. This is especially important when working with highly volatile or non-standard chemicals that there may not be a large amount of information to kind of base what your expected recovery should be. When working with data from passive samplers, it can be daunting at first. The data you're going to receive from the lab is going to
be, or at least it needs to be, sometimes it doesn't always come from the lab this way, but it should be in the terms of the amount of chemical present and in the passive samplers. So, you should get something in units, for example, nanograms per SPMD. Although this can be informative, you can still compare sites you can talk about presence, absence, relative differences between sites. Often the typical goal is to express the data in terms of an estimated time, time weighted average, water concentration. The methods to get to this water concentration varying complexity depending on the type of sample used and the degree of understanding of the uptake kinetics for the sampler. This can
be as simple as a single one step single equation to a multi-step process that incorporates PRC's and sophisticated uptake models. For SPND's, which is one that has a lot of understanding on, and very well-defined update models, this is where we start dealing with that multi-step process to get from a sampler concentration to a water concentration. To simplify that, USGS has created some downloadable and customizable spreadsheets. They really make it as simple
as insert your data from the lab in the yellow cells and the water concentration comes out in the blue cells. But now you have data, so what does it mean? Results from passive samplers represent the time weighted average concentration of chemical over that deployment period. The fact that the data is a time-weighted average, it's impossible to know the maximum concentration of events or when they happened in the deployment period as we talked about earlier. Although it may not be possible to calculate time-weighted average
water concentrations for all chemicals that you may measure in a passive sampler, that doesn't mean you still can't get some good information. To be able to calculate water concentrations, you either have to have knowledge of experimentally derived sampling rates for each chemical, or have well defined uptake models that can use different chemical parameters to help perform those calculations. Data expresses the amount of chemical per sampler can still be informative. However, you need to look at your study goals to determine if a past
example can meet your needs. If it is absolutely critical that you need to have a water concentration expresses nanograms per liter or whatnot of chemical acts, looking and make sure that passive sampler is able to give you that type information. Because as I said, you either need to know what sampling rates are, you gotta have very good models to be able to do it, and for not all samplers in chemicals is that possible. It's human nature to want to compare data from a passive sampler to judicial sampling techniques. I'm the first
one that will say if the two numbers match, I wanna say hey great, look how good these numbers were in agreement. But in reality, it's an apple to oranges type of comparison. All of the data can be similar. One must be careful in making these comparisons. Really, because of the differences in the information, each sampling activity provides, unless you're doing a rigorous graph sampling regime where you're collecting a lot of samples over the time period, there's no reason to expect that a single data point is representative to the average conditions over weeks to months as you would get from a passive sampler. Not the one is better or worse than the other. All the sampling techniques provide very useful information, and it depends on the question being asked, on what type of sample will best to provide the information you need. And really, you need to think about these different sampling
techniques as being complementary techniques. Not necessarily always interchangeable. So, in the little bit of time I got left, I'm just going to kind of run through a couple examples real quick. In the months following the Deepwater Horizon spill, there were hundreds of SPND's deployed along the Gulf Coast from multiple agencies to monitor the presence of pH's near sensitive marine habitats. Depending on the site, SPMD's were deployed at depths anywhere between 1
and 69 meters. Average depth seems to be about 16 meters from the data that I've seen. This figure shows comparison between the relative abundance of pH's and deployed SPND's and that from the floating oils. As you can see, there's a pretty good agreement in the composition pH's that depth that was measured and SPMD's compared to that from the floating oils. As part of our response to two separate oil spills on the Yellowstone River in Montana, SPMD's were deployed at multiple locations and multiple time periods to determine the spatial and temporal distribution of petroleum hydrocarbons. Following the spill, this data was used, along with observations from captured fish, to determine the potential exposure to dissolve pH's is to resident fish species. The data showed that the lighter pH's dominated the container profiles and were the ones most susceptible to downstream transport. And you can see that
from all the peaks in that first half of the chromatogram there. Although the samplers were used in the study as part of the response, this is a case to where samplers like this could also be useful during assessment and restoration phases as they can evaluate changes in chemical concentrations over time, especially as the chemical concentrations continued to fall to levels that maybe more difficult to measure with the traditional grab sample. Again, looking at oil related issues, the Norwegian Institute for Water Research, or NIVA, conducted a study using SPMD's and POCIS in the North Sea to determine the extent of contamination from a petroleum hydrocarbons as well as alkylphenols in produced waters from offshore oil platforms. The samplers were deployed at intervals up and down a gradient based on the prevailing currents around the platforms. Short chain alcohol phenols and lighter pH is typically the alkylated naphthalenes, phenanthrene's and dibisothiophenes were consistently measured within a one to two kilometres of the discharge point. While the concentration is measured were typically less than fifty nanograms per liter, which was orders of magnitude lower than levels reported to give acute or sub lethal effects. There is always the potential
for long term consequences which are currently unknown. Early on I talked about, you know, some extreme uses of samplers, as far as extreme conditions. Typically, we think of passive samplers as a tool to be used in relatively shallow waters for periods of weeks to months.
This example was by the Royal Netherlands at Super Sea Research, where they investigated the potential of passive sampling techniques to measure organic contaminants at deep ocean sites. They deployed SPMD's at depths up to five kilometers, for periods of one, to one and a half years at sites in the North Atlantic Ocean and Indian Ocean. What they found was concentrations of pH's, PCB's, Hexachlorobenzene and DDE were measured across all the depth gradients. The data suggested that affection of surface waters down to a depth of about
one kilometer was an important mechanism for contaminant transport into the deep ocean. Probably to me the highlight of this whole study was that it showed, although it was extremely challenging, it is possible to use passive samplers and some of the more extreme conditions that we would have on the planet. An example of linking the chemistry to the biology was a study that we did use an SPMD where they were deployed at 69 sites over a two-year period and tributaries across all five of the Great Lakes. 150 of the 184 chemicals
targeted were detected at least once and typically, as you would expect were highly complex mixtures of chemicals. The chemical data was then entered into the ToxCast database from EPA, which contains toxicological information from hundreds of assays for over nine thousand chemicals. Information we were able to get back from ToxCast allowed us to calculate the ratio of water concentrations and activity concentration from those ToxCast. assays to determine exposure activity ratios, or EARs. As you see in this figure here, EARs were estimated for each
chemical, and then we could use that data to rank the cumulative potential of chemicals present that may elicit some sort of biological response. As you can see pretty easily, sites around Lake Michigan and Lake Erie tended to have the highest risk to aquatic organisms. High EAR values indicating greater potential risk for many chemical classes tend to be correlated with urban land cover and areas that received high amounts of wastewater effluent influence. But as you moved into the more rural areas, we saw different responses that tended to be linked more to herbicides as well as flame fire retardants. The last case
study one show here is looking at metals. In this case study medals were sampled using SLMD to measure concentrations in a large river system that received mining waste. In this example you can see in the lower picture that SLMD was embedded in a rock, which then was lowered to this the bed sediment. That rock allowed the sampler to stay in place as well as maintained the sampler positioning on the settlement to be able to measure what that metal concentration was that the sediment water interface. as you can see from the data figure there on the right. in the red circle, concentrations of Copper, in this case at
this particular site, did tend to fall within a suspected effects range. So, it was a good technique to try to measure potential risk to organisms at a particular level of the river system. So, to sort of wrap this up, there are a lot of established methods for sampling chemicals from the environment. The body of work over the last few decades is demonstrated that
passive sampling techniques are a viable option for providing data on dissolved concentrations of chemicals in an environment. The types of passive samplers available for use in the body of knowledge surrounding these samplers as rapidly expanding. Therefore, when you go to select the type of passive sampler you need to make sure that that particular sampler can answer the question of your study because not all samplers are developed to the same level. And remember, although informative passive samplers providing information that should be considered complementary to other sampling techniques. So again, a grab sample
is not a passive sampler and vice versa. In 2010 a fact sheet was prepared by USGS to provide basic overview of using SPND's to sample oil spills. This fact sheet also provides some practical considerations to aid users in designing their studies. Also shown here is a how to guide we put together
back in 2010 that provides tips and items for consideration for using passive samplers. This guide is sort of a cradle to grave, everything from designing the study, to going into the field, to picking a laboratory, to understanding your data. It is tailored towards the SPMD's but the information presented in here is largely applicable to about any type of passive sampler you may choose to use. And with that I'll thank you for attending today and I'm happy to answer any questions you have in a little time we have left and my contact information is on the screen there if you would like to reach out to me with more questions in the future.
[Moderator Jo Ellen Hinck] Thank you. If you're interested in asking a question, you can come off mute and or use the raise hand function. As we're waiting for that Dave, quick question. Can you comment on price point? I mean, I know pH analysis can get quite costly. Any brief comment you can make in terms of price comparisons? [Dr. Dave Alvarez] Every sample definitely has its associated costs. You know, I think if all you needed was like one sample point, then a grab sample is obviously going to be cheaper than a passive because the passive we got all the hardware and everything that goes with it. If it's something where you're gonna need to sample overtime, then the passive is going to be much cheaper because in the end you only got one analysis and the reality is the analytical end is where all the money goes. So, I think the samplers are nowhere
near as expensive as what people may think they're going to be and everyone's got different options and prices. Many samplers are commercially available. I think the price point could be all over the place, so kind of hard to really say. [Jo Ellen Hinck] Thanks yeah, so if you have a question, you can come off mute and there's also some resources that Dave had mentioned on his slides that are also in the chat that you can link to directly.
[Jeremy Buck] Hi, this is Jeremy Buck. Just a question on if you can comment on differences in deployments in marine versus freshwater versus estuarine, brackish, and if there's a need to kind of make adjustments for any saline condition’s differences? [Dave Alvarez] There's always exceptions with certain chemicals that may behave differently, but for the most part from what we've seen, both in laboratory studies and field studies, there's not really any noticeable impact on the performance of most samplers, especially things like SPMD's or the PED's, things that are going more for those hydrophobic regulated contaminants. We do see differences and this is probably more in brackish water and I'm not a marine guy so I have no way of knowing how to predict but some sites you just get a lot more growth of stuff. I mean, we've had deployment canisters that have come out
of some sites that were so full and the inside of barnacles that we literally were chiseling out our samplers. And then we have other sites that come out and they are crystal clean and look like they've never been deployed so, yeah, I have no idea how to predict that. But as far as performance of the samplers I would not expect that you'd have any real considerations. So tomorrow more of a difference in potential fouling conditions that you encounter. I would say it's more on the logistical side than sampler performance. OK thanks.
[Jo Ellen Hinck] Well, not hearing any more questions, I just want to thank Dave once again for your presentation and we will get that posted and I will also put, or, Dave, maybe you can just drop your email in the chat so it's readily available for folks in case they do have follow up questions for you. [Dave Alvarez] Yeah, I'll do that right now. [Jo Ellen Hinck] Wonderful, well thanks everyone. Have a great rest of your day and we hope to see you next time. [Dave Alvarez] Thanks, everybody.