Contaminants of Concern in Aquatic Species
Nancy Denslow Ph.D. shares her studies of fish and other aquatic species that reveal a need to further study contaminants in water bodies and their impact on the environment and human health.
Featuring:
• Dr. Denslow’s research involves developing and using molecular biomarkers to evaluate changes in gene expression depending on stress or exposure to contaminants. For environmental species, molecular approaches, including microarray analysis and proteomics, were developed for several non-model species, including fish, gastropods, and coral.
Fish swim in waters that are contaminated by superfund chemicals and emerging contaminants of concern and, thus, provide a direct measure of effects of the contaminants in vertebrates. Many of the chemicals behave as endocrine disruptors and, in particular, as estrogen mimics. To better study the direct effects of these contaminants on reproduction, three largemouth bass estrogen receptors (alpha and two beta-like subtypes) were isolated, sequenced, and integrated into expression assays. The receptors appear to bind and are activated differentially by organochlorine pesticides. In addition, the tissue expression patterns are different for the three receptors.
• Here is a 2018 video that highlights her work:
https://www.youtube.com/watch?v=fno2p373ML8
• Dr. Denslow loves solving problems and the problem of environmental impact on health is an important one. She and UF has been thought of as pioneers in applying molecular tools to looking at fish and fish health and by implication to human health
• She can talk about linkages between pesticide exposures (fracking waters and what they do to fish) as well as linkages between pesticide exposures and chronic dlseases like lupus (in other words topic can focus on fish and aquatic species but there are definite TRANSLATIONAL aspects to this work as well (impacts on humans and plants)
Nancy Denslow, Ph.D.
Nancy Denslow is a professor in the UF College of Veterinary Medicine’s Department of Physiological Sciences and in the Center for Environmental and Human Toxicology and a joint professor in the Department of Biochemistry and Molecular Biology at the University of Florida. Nancy has pioneered the use of molecular technologies for environmental toxicology especially focusing on high throughput in vitro assays, biomarker development and toxicogenomics approaches for evaluating contaminants of emerging concern. She also directs the UF Aquatic Toxicology Laboratory.• Dr. Denslow’s research involves developing and using molecular biomarkers to evaluate changes in gene expression depending on stress or exposure to contaminants. For environmental species, molecular approaches, including microarray analysis and proteomics, were developed for several non-model species, including fish, gastropods, and coral.
Fish swim in waters that are contaminated by superfund chemicals and emerging contaminants of concern and, thus, provide a direct measure of effects of the contaminants in vertebrates. Many of the chemicals behave as endocrine disruptors and, in particular, as estrogen mimics. To better study the direct effects of these contaminants on reproduction, three largemouth bass estrogen receptors (alpha and two beta-like subtypes) were isolated, sequenced, and integrated into expression assays. The receptors appear to bind and are activated differentially by organochlorine pesticides. In addition, the tissue expression patterns are different for the three receptors.
• Here is a 2018 video that highlights her work:
https://www.youtube.com/watch?v=fno2p373ML8
• Dr. Denslow loves solving problems and the problem of environmental impact on health is an important one. She and UF has been thought of as pioneers in applying molecular tools to looking at fish and fish health and by implication to human health
• She can talk about linkages between pesticide exposures (fracking waters and what they do to fish) as well as linkages between pesticide exposures and chronic dlseases like lupus (in other words topic can focus on fish and aquatic species but there are definite TRANSLATIONAL aspects to this work as well (impacts on humans and plants)
Transcription:
Melanie Cole (Host): Welcome to UF Vet Med Voice with the University of Florida College of Veterinary Medicine. I'm Melanie Cole. And today, my guest shares her studies of fish and other aquatic species to reveal a need to further study contaminants in water bodies and their impact on the environment and human health. We're discussing contaminants of concern in aquatic species. And joining me is Dr. Nancy Denslow. She's a professor and Associate Chair of Physiological Sciences and the Director of UF's Aquatic Toxicology Laboratory in the Center for Environmental and Human Toxicology at the University of Florida College of Veterinary Medicine.
Dr. Denslow, it's a pleasure to have you join us today. So can you tell us a little bit about your work as an environmental toxicologist and molecular diagnostician with special interest in diseases of reptiles and amphibians? Tell us a little bit about what you do.
Dr Nancy Denslow: Well, so my background is actually in biochemistry and molecular biology. And I'm also doing environmental toxicology. So I'm interested in contaminants that are out there in the environment and what they might be doing to the fish that live out in the environment. We use fish as a model because they are actually swimming in the water bodies where the contaminants are sometimes appearing, you know, either from sewage wastewater or from actual runoff or some other way, but that's where the contaminants are appearing.
Melanie Cole (Host): Well, then let's expand on that, on the contaminants of concern in aquatic species and really their impact on the environment. Can you share your research that involves developing and using molecular biomarkers to evaluate changes in gene expression depending on the stress or the exposure to those contaminants?
Dr Nancy Denslow: So we use a variety of fish models for our work. We use largemouth bass because they're an apex fish and they are economically very important. And so fish swim where the contaminants are found and they're sensitive to environmental contaminants and their populations may be impacted. They are at the very top of the food chain and they're eaten by people, so there's a connection to human health.
So among the fish models that we use, as I mentioned, are largemouth bass, fathead minnows, zebrafish, mosquitofish, and other fish of that sort. Some are small fish and some are large fish, like the largemouth bass. And we've been interested for example in endocrine disruptors. So endocrine disruptors are chemicals that behave as hormones and interfere with how the endogenous hormones work. So they behave as estrogens or estrogen mimics or androgens or inhibit their metabolism of the endogenous hormones. And so if these hormones or mimics get into the fish, it can alter the physiology of the fish, so then the fish don't reproduce very well or they might have other issues. Among the chemicals that we have done a lot of work with are the legacy pesticides, such as the organic chlorine pesticides.
Melanie Cole (Host): Well then, can you talk about the link between pesticide exposures as well as the linkages between those exposures and chronic disease like lupus? And as we know our focus is on fish and aquatic species, but there are definitely translational aspects to this work, as well as impact on humans and plants, right?
Dr Nancy Denslow: Absolutely. So we've been in contact with the Lake Apopka Farmworkers, and this is a group of people that used to work the farms on the north shore of Lake Apopka, where a lot of pesticides were used in the past. While those pesticides were eliminated in the 1970s, you know, they still have pesticide residue in their blood and many of them have lupus. So, they didn't know or we don't know exactly what the relationship is between the exposure to these pesticides and lupus.
But when we take largemouth bass and expose them to the same contaminants that were used on those farms such as DDE or methoxychlor or toxaphene and so on, we find that at the molecular level, it alters gene expression, such that among the pathways that are found are the ones that we expected to see, the endocrine changes. For example, vitellogenin, some of these contaminants are estrogens and they result in increasing the production of proteins or expression of genes that are controlled by estrogen, such as vitellogenin. And so you see exactly what you expect that these are endocrine disruptors.
What we didn't know at the time we did the experiment was that these contaminants also alter immune function. And among the pathways that came up with our molecular analysis were pathways that were related to lupus, so perhaps there is a connection. I don't know if fish get lupus, they probably don't. But the pathways are conserved between fish and humans. And so if these pathways that are conserved in both animals are accelerated due to the contaminant exposure. It's possible, it may be even likely that the lupus that these farm workers are experiencing came from their previous exposures when they were working on the farm.
They mentioned that the planes would fly overhead while they were out there picking fruits and vegetables and they would spray them and spray their food, their water source. So they were fairly highly exposed and they, like I said, still have residue of these pesticides in their blood that exceeds what normal people have, that are above the 90th percentile that people have shown for the NHANES. And NHANES is National Health and Nutrition Examination Survey. And some of these people even still had DDT in their blood, which is amazing after so many years, that we could measure that in their blood. So they must have been exposed heavily to these chemicals.
Melanie Cole (Host): Wow. It's really amazing what you can find out even so many years later, Dr. Denslow. So tell us how the University of Florida College of Veterinary Medicine has built a reputation as a leader in the area of environmental toxicology due to this pioneering research we're discussing here today. Tell us a little bit about your team and what you do.
Dr Nancy Denslow: So in our center, we have excellent faculty members. All of us do environmental research. We each have a different aspect that we work on mostly, but several of us work with fish, but we also work with other animal models. For example, I have a graduate student working with manatees, and so she is an expert on that. And also we work with rodents in the facility and so on. But we all are worried about contaminants of emerging concern and whether they might have an effect on these animal models that we work with or even with people. So we have a group in our center that does risk assessment, and they're excellent at doing that as well.
So together, we all work very nicely, you know. And we help each other out and we do projects together and write papers together. And so it's really fun to be part of this group.
Melanie Cole (Host): Well, building on that body of work that's including the pioneering development of molecular tools and biomarkers as we were talking a little bit before to evaluate fish and fish health, how do you see this translating to humans and even other species and plants? What are some of the possible implications of your research and what we've been discussing here?
Dr Nancy Denslow: Well, as I mentioned already, fish are vertebrates and so are humans. And so many of the molecular pathways that exist in humans also exist in fish. And so instead of using a rat model or some other mammalian model, we could use fish directly, which is less worrisome in terms of animal usage.
And so because the molecular pathways are the same, we can determine in the fish if there is a particular pathway that is affected by an exposure to a contaminant of emerging concern. And of course, right now, endocrine disruption has been something that for the last 20 years, people have begun to notice that there are a lot of contaminants out in the environment that alter the responses of physiology and that these interfere with normal hormone work in the body. For example, interfere with estrogen signaling or androgen signaling or so on. And so we're all very concerned about that because if it affects fish, it probably also affects humans.
Melanie Cole (Host): It's fascinating. And as we wrap up, Dr. Denslow, I understand you're also looking at emerging problems, such as what happens to fish when hydraulic fracturing or fracking fluid produces during extreme forms of energy production contaminates our lakes and ponds. Can you briefly describe this work for the listeners and what you would like the takeaway from this podcast to be? It's so important.
Dr Nancy Denslow: Yes, we've been working with fracking-produced waters. And when fracking occurs, they inject a high pressure of water into the system to help release the gas and that water that's used gets recycled. And also they have chemicals that are introduced into that water among which are acrylamides. And I guess that helps to stabilize the underground when they fracture it to release the gas.
So these produced waters actually contain a lot of elements in them and contain polyaromatic hydrocarbons. And so we did an exposure of fathead minnows with these waters and found that they could be very toxic. But at the molecular level, what was fascinating was to see that they really turned on pathways that were related to cancer. So, I think exposure to these kinds of waters is something that we don't want people to have. And they need to be regulated, these waters, and maybe they have to figure out a way to dispose of them correctly, so that they do not enter waterways and harm the aquatic biota or even people that might use that water for drinking water or some other source.
Melanie Cole (Host): Such important research that you're doing, Dr. Denslow. Thank you so much for joining us today. To listen to more podcasts from the experts at the University of Florida College of Veterinary Medicine, please visit vetmed.ufl.edu. That concludes today's episode of UF Vet Med Voice brought to you by the University of Florida College of Veterinary Medicine, advancing animal, human and environmental health. I'm Melanie Cole.
Melanie Cole (Host): Welcome to UF Vet Med Voice with the University of Florida College of Veterinary Medicine. I'm Melanie Cole. And today, my guest shares her studies of fish and other aquatic species to reveal a need to further study contaminants in water bodies and their impact on the environment and human health. We're discussing contaminants of concern in aquatic species. And joining me is Dr. Nancy Denslow. She's a professor and Associate Chair of Physiological Sciences and the Director of UF's Aquatic Toxicology Laboratory in the Center for Environmental and Human Toxicology at the University of Florida College of Veterinary Medicine.
Dr. Denslow, it's a pleasure to have you join us today. So can you tell us a little bit about your work as an environmental toxicologist and molecular diagnostician with special interest in diseases of reptiles and amphibians? Tell us a little bit about what you do.
Dr Nancy Denslow: Well, so my background is actually in biochemistry and molecular biology. And I'm also doing environmental toxicology. So I'm interested in contaminants that are out there in the environment and what they might be doing to the fish that live out in the environment. We use fish as a model because they are actually swimming in the water bodies where the contaminants are sometimes appearing, you know, either from sewage wastewater or from actual runoff or some other way, but that's where the contaminants are appearing.
Melanie Cole (Host): Well, then let's expand on that, on the contaminants of concern in aquatic species and really their impact on the environment. Can you share your research that involves developing and using molecular biomarkers to evaluate changes in gene expression depending on the stress or the exposure to those contaminants?
Dr Nancy Denslow: So we use a variety of fish models for our work. We use largemouth bass because they're an apex fish and they are economically very important. And so fish swim where the contaminants are found and they're sensitive to environmental contaminants and their populations may be impacted. They are at the very top of the food chain and they're eaten by people, so there's a connection to human health.
So among the fish models that we use, as I mentioned, are largemouth bass, fathead minnows, zebrafish, mosquitofish, and other fish of that sort. Some are small fish and some are large fish, like the largemouth bass. And we've been interested for example in endocrine disruptors. So endocrine disruptors are chemicals that behave as hormones and interfere with how the endogenous hormones work. So they behave as estrogens or estrogen mimics or androgens or inhibit their metabolism of the endogenous hormones. And so if these hormones or mimics get into the fish, it can alter the physiology of the fish, so then the fish don't reproduce very well or they might have other issues. Among the chemicals that we have done a lot of work with are the legacy pesticides, such as the organic chlorine pesticides.
Melanie Cole (Host): Well then, can you talk about the link between pesticide exposures as well as the linkages between those exposures and chronic disease like lupus? And as we know our focus is on fish and aquatic species, but there are definitely translational aspects to this work, as well as impact on humans and plants, right?
Dr Nancy Denslow: Absolutely. So we've been in contact with the Lake Apopka Farmworkers, and this is a group of people that used to work the farms on the north shore of Lake Apopka, where a lot of pesticides were used in the past. While those pesticides were eliminated in the 1970s, you know, they still have pesticide residue in their blood and many of them have lupus. So, they didn't know or we don't know exactly what the relationship is between the exposure to these pesticides and lupus.
But when we take largemouth bass and expose them to the same contaminants that were used on those farms such as DDE or methoxychlor or toxaphene and so on, we find that at the molecular level, it alters gene expression, such that among the pathways that are found are the ones that we expected to see, the endocrine changes. For example, vitellogenin, some of these contaminants are estrogens and they result in increasing the production of proteins or expression of genes that are controlled by estrogen, such as vitellogenin. And so you see exactly what you expect that these are endocrine disruptors.
What we didn't know at the time we did the experiment was that these contaminants also alter immune function. And among the pathways that came up with our molecular analysis were pathways that were related to lupus, so perhaps there is a connection. I don't know if fish get lupus, they probably don't. But the pathways are conserved between fish and humans. And so if these pathways that are conserved in both animals are accelerated due to the contaminant exposure. It's possible, it may be even likely that the lupus that these farm workers are experiencing came from their previous exposures when they were working on the farm.
They mentioned that the planes would fly overhead while they were out there picking fruits and vegetables and they would spray them and spray their food, their water source. So they were fairly highly exposed and they, like I said, still have residue of these pesticides in their blood that exceeds what normal people have, that are above the 90th percentile that people have shown for the NHANES. And NHANES is National Health and Nutrition Examination Survey. And some of these people even still had DDT in their blood, which is amazing after so many years, that we could measure that in their blood. So they must have been exposed heavily to these chemicals.
Melanie Cole (Host): Wow. It's really amazing what you can find out even so many years later, Dr. Denslow. So tell us how the University of Florida College of Veterinary Medicine has built a reputation as a leader in the area of environmental toxicology due to this pioneering research we're discussing here today. Tell us a little bit about your team and what you do.
Dr Nancy Denslow: So in our center, we have excellent faculty members. All of us do environmental research. We each have a different aspect that we work on mostly, but several of us work with fish, but we also work with other animal models. For example, I have a graduate student working with manatees, and so she is an expert on that. And also we work with rodents in the facility and so on. But we all are worried about contaminants of emerging concern and whether they might have an effect on these animal models that we work with or even with people. So we have a group in our center that does risk assessment, and they're excellent at doing that as well.
So together, we all work very nicely, you know. And we help each other out and we do projects together and write papers together. And so it's really fun to be part of this group.
Melanie Cole (Host): Well, building on that body of work that's including the pioneering development of molecular tools and biomarkers as we were talking a little bit before to evaluate fish and fish health, how do you see this translating to humans and even other species and plants? What are some of the possible implications of your research and what we've been discussing here?
Dr Nancy Denslow: Well, as I mentioned already, fish are vertebrates and so are humans. And so many of the molecular pathways that exist in humans also exist in fish. And so instead of using a rat model or some other mammalian model, we could use fish directly, which is less worrisome in terms of animal usage.
And so because the molecular pathways are the same, we can determine in the fish if there is a particular pathway that is affected by an exposure to a contaminant of emerging concern. And of course, right now, endocrine disruption has been something that for the last 20 years, people have begun to notice that there are a lot of contaminants out in the environment that alter the responses of physiology and that these interfere with normal hormone work in the body. For example, interfere with estrogen signaling or androgen signaling or so on. And so we're all very concerned about that because if it affects fish, it probably also affects humans.
Melanie Cole (Host): It's fascinating. And as we wrap up, Dr. Denslow, I understand you're also looking at emerging problems, such as what happens to fish when hydraulic fracturing or fracking fluid produces during extreme forms of energy production contaminates our lakes and ponds. Can you briefly describe this work for the listeners and what you would like the takeaway from this podcast to be? It's so important.
Dr Nancy Denslow: Yes, we've been working with fracking-produced waters. And when fracking occurs, they inject a high pressure of water into the system to help release the gas and that water that's used gets recycled. And also they have chemicals that are introduced into that water among which are acrylamides. And I guess that helps to stabilize the underground when they fracture it to release the gas.
So these produced waters actually contain a lot of elements in them and contain polyaromatic hydrocarbons. And so we did an exposure of fathead minnows with these waters and found that they could be very toxic. But at the molecular level, what was fascinating was to see that they really turned on pathways that were related to cancer. So, I think exposure to these kinds of waters is something that we don't want people to have. And they need to be regulated, these waters, and maybe they have to figure out a way to dispose of them correctly, so that they do not enter waterways and harm the aquatic biota or even people that might use that water for drinking water or some other source.
Melanie Cole (Host): Such important research that you're doing, Dr. Denslow. Thank you so much for joining us today. To listen to more podcasts from the experts at the University of Florida College of Veterinary Medicine, please visit vetmed.ufl.edu. That concludes today's episode of UF Vet Med Voice brought to you by the University of Florida College of Veterinary Medicine, advancing animal, human and environmental health. I'm Melanie Cole.