A case study of temporal trends in risk factors associated with endocrine disruption in smallmouth bass
Issue
The USGS has a long-term research effort that identified endocrine disruption in smallmouth bass (SMB) in the Chesapeake Bay watershed. Endocrine disruption can cause many changes in fish, including intersex characteristics where fish develop characteristics of the other sex, such as immature eggs forming in males. An overview by USGS of endocrine disruption in fish found the condition downstream of wastewater treatment plants and in watersheds dominated by agricultural land use; however, no single cause or environmental stressor has been directly identified (Blazer and others, 2021). To better understand the risk factors associated with SMB endocrine disruption, the USGS conducted monitoring and analysis at a site in the Potomac River Basin to assess effects of agricultural land use. The results from these research efforts are informing several outcomes of the Chesapeake Watershed Agreement, including a better understanding of the occurrence and effects of contaminants, improving water quality, and restoring fish habitat.
USGS Study
The collaborative monitoring program, conducted by the USGS and Maryland Department of Natural Resources (MD DNR) was conducted at a site located near the confluence of Antietam Creek and the Potomac River in Dargan, Maryland (figure 1).
The aim of this study was to learn how exposure to individual and complex contaminant mixtures changes seasonally and annually, particularly during key SMB developmental lifestages, and to identify how biological indicators at the molecular, cellular, tissue, individual, and SMB population levels respond to these exposures. In particular, the SMB population at Dargan, Maryland has significantly declined over the past decade and more than half of the land use in this area is either agriculture or development.
A unique aspect of the study was to collect both surface-water samples and fish, during multiple seasons over a 7-year period to assess the changes in the life cycle of SMB. Monthly or biweekly analyses of over 300 surface water chemicals with adult SMB fish health assessments in spring (pre-spawn) and fall (recrudescence, when SMB start to prepare for spring spawning) were conducted from 2013–2019. Approximately 20 SMB were collected by MD DNR at each time period and analyzed by the USGS.
The USGS assessment focused on changes in liver and testis gene transcripts associated with reproduction (molecular), changes in microscopic indicators of multiple tissues (cellular), and organismal health indicators such as oganosomatic indices and condition factor (measures of fitness), and visible abnormalities. The study applied a unique set of biological effects indicators to assess endocrine disruption including:
- Testicular oocytes (TO): also known as intersex, can be measured for prevalence and severity and is generally induced during early SMB development.
- Plasma vitellogenin: a protein associated with egg yolk development; a response that occurs in days to months.
- Reproductive gene transcripts: measures changes in a biological response that occurs in hours to days.
Major Findings
The integration of chemical monitoring with biological effects provided a deeper understanding of risk factors for observed adverse effects in SMB. Some of the major findings included:
Of the 300 contaminants analyzed in surface water, there was a wide range of occurrence but many of the compounds were not detected.
- Of the 20 hormones and sterols analyzed, eight were detected at least once, including six hormones (testosterone, cis-androsterone, estrone, 17-alpha estradiol, 17-beta estradiol, and trans-diethylstilbestrol), and two sterols (3-beta-coprostanol and cholesterol).
- For the phytoestrogens, coumesterol was not detected while five others occurred commonly throughout the study (biochanin A, daidzein, equol, formononetin, and genestein).
- Of the 107 pharmaceutical analytes, 32 were detected. The nine most commonly detected were lidocaine, fexofenadine, venlafaxine, metformin, methyl-1H-benzotriazole, desvenlafaxine, methocarbamol, tramadol, and carbamazepine.
- Of the 105 common use pesticides analyzed, 16 were detected with the three most commonly detected being simazine, atrazine, and metolachlor.
The biological effects monitoring documented changes in SMB reproductive health indicators.
Several of the reproductive indicators varied over time:
- Abundance of heptic vitellogenin transcripts was high in males during the early years of the study but decreased over time except for 2018 (figure 2a). It was also high in females during the early years and varied in the following years (figure 2b).
- Overall males and females exhibited similar trends in plasma vitellogenin, with the highest concentrations in spring of 2013 and 2015 (figure 2a and b) which were reduced by half starting in spring 2016.
- Prevalence of TO remained high throughout the study (figure 2c) and both TO prevalence and severity were highest in the spring and fall of 2016, corresponding with a high peak in atrazine (figure 3).
- Analysis of contaminant exposures during early development showed that TO development may have been affected by pesticide application within the immediate catchment.
- Peak concentrations of multiple chemicals contributed to the complex mixtures potentially affecting bass during the spring (spawning), early summer (early juvenile development) and fall (recrudescence)
Sources/Usage: Public Domain. View Media DetailsFigure 2. Annual and seasonal changes in plasma vitellogenin (Vtg) and hepatic vitellogenin (vtg) gene transcripts in A) female and B) male smallmouth bass. C) Prevalence and severity of testicular oocytes (TO) in male smallmouth bass.
The changes in the biological indicators were related to several factors:
- Multiple agriculture-related contaminants or land-use patterns were associated with TO, plasma vitellogenin, and gene transcript abundance in both male and female SMB. In males, positive associations between TO severity and pesticide application in the immediate catchment, plasma vitellogenin and total estrogenicity, and vitellogenin transcripts with high phytoestrogen cover crops were identified. In females, positive associations between plasma vitellogenin and the isoflavone, formononetin, and estrogen receptor transcripts (involved in vitellogenin production) with simazine and cholesterol were identified.
- The prevalence of TO and detectable levels of plasma vitellogenin and liver and testis vitellogenin transcripts were high throughout the study. However, vitellogenin, which is induced within hours to days (gene transcripts) and may persist for months (in plasma), did vary considerably by season and year (figure 2).
- Peaks of complex mixtures of numerous contaminants occurred during the spring/early summer when spawning and early development occurs and to a lesser extent in fall/winter during recrudescence.
Management and Research Applications
- This study identified numerous contaminants that will be considered for future laboratory exposure studies. This will help to identify cause and effect relationships between individual contaminants and biological changes associated with exposure which cannot be directly linked in wild fish.
- Based on the reproductive changes identified in females from this study, future research will also include gene transcript analysis from the ovary of female SMB.
- Land-use practices within the immediate and upstream catchments that may be associated with the release of these contaminants were identified and signify the importance of scale in monitoring studies.
For more information
- The results of this study were published in Ecotoxicology (with open access) at A case study: temporal trends of environmental stressors and reproductive health of smallmouth bass (Micropterus dolomieu) from a site in the Potomac River Watershed, Maryland, USA.
- Accompanying data release: Water chemistry and smallmouth bass biological data from the Potomac River, Dargan, Maryland, 2013-2019
- Blazer and others: Read a previous USGS summary of about intersex conditions include Land-use influences on estrogenic-endocrine disruption in fish within the Chesapeake Bay watershed
- Please contact Heather Walsh for more information at hwalsh@usgs.gov.
Land-use influences on estrogenic-endocrine disruption in fish within the Chesapeake Bay watershed
Issue
The USGS has a long-term research effort that identified endocrine disruption in smallmouth bass (SMB) in the Chesapeake Bay watershed. Endocrine disruption can cause many changes in fish, including intersex characteristics where fish develop characteristics of the other sex, such as immature eggs forming in males. An overview by USGS of endocrine disruption in fish found the condition downstream of wastewater treatment plants and in watersheds dominated by agricultural land use; however, no single cause or environmental stressor has been directly identified (Blazer and others, 2021). To better understand the risk factors associated with SMB endocrine disruption, the USGS conducted monitoring and analysis at a site in the Potomac River Basin to assess effects of agricultural land use. The results from these research efforts are informing several outcomes of the Chesapeake Watershed Agreement, including a better understanding of the occurrence and effects of contaminants, improving water quality, and restoring fish habitat.
USGS Study
The collaborative monitoring program, conducted by the USGS and Maryland Department of Natural Resources (MD DNR) was conducted at a site located near the confluence of Antietam Creek and the Potomac River in Dargan, Maryland (figure 1).
The aim of this study was to learn how exposure to individual and complex contaminant mixtures changes seasonally and annually, particularly during key SMB developmental lifestages, and to identify how biological indicators at the molecular, cellular, tissue, individual, and SMB population levels respond to these exposures. In particular, the SMB population at Dargan, Maryland has significantly declined over the past decade and more than half of the land use in this area is either agriculture or development.
A unique aspect of the study was to collect both surface-water samples and fish, during multiple seasons over a 7-year period to assess the changes in the life cycle of SMB. Monthly or biweekly analyses of over 300 surface water chemicals with adult SMB fish health assessments in spring (pre-spawn) and fall (recrudescence, when SMB start to prepare for spring spawning) were conducted from 2013–2019. Approximately 20 SMB were collected by MD DNR at each time period and analyzed by the USGS.
The USGS assessment focused on changes in liver and testis gene transcripts associated with reproduction (molecular), changes in microscopic indicators of multiple tissues (cellular), and organismal health indicators such as oganosomatic indices and condition factor (measures of fitness), and visible abnormalities. The study applied a unique set of biological effects indicators to assess endocrine disruption including:
- Testicular oocytes (TO): also known as intersex, can be measured for prevalence and severity and is generally induced during early SMB development.
- Plasma vitellogenin: a protein associated with egg yolk development; a response that occurs in days to months.
- Reproductive gene transcripts: measures changes in a biological response that occurs in hours to days.
Major Findings
The integration of chemical monitoring with biological effects provided a deeper understanding of risk factors for observed adverse effects in SMB. Some of the major findings included:
Of the 300 contaminants analyzed in surface water, there was a wide range of occurrence but many of the compounds were not detected.
- Of the 20 hormones and sterols analyzed, eight were detected at least once, including six hormones (testosterone, cis-androsterone, estrone, 17-alpha estradiol, 17-beta estradiol, and trans-diethylstilbestrol), and two sterols (3-beta-coprostanol and cholesterol).
- For the phytoestrogens, coumesterol was not detected while five others occurred commonly throughout the study (biochanin A, daidzein, equol, formononetin, and genestein).
- Of the 107 pharmaceutical analytes, 32 were detected. The nine most commonly detected were lidocaine, fexofenadine, venlafaxine, metformin, methyl-1H-benzotriazole, desvenlafaxine, methocarbamol, tramadol, and carbamazepine.
- Of the 105 common use pesticides analyzed, 16 were detected with the three most commonly detected being simazine, atrazine, and metolachlor.
The biological effects monitoring documented changes in SMB reproductive health indicators.
Several of the reproductive indicators varied over time:
- Abundance of heptic vitellogenin transcripts was high in males during the early years of the study but decreased over time except for 2018 (figure 2a). It was also high in females during the early years and varied in the following years (figure 2b).
- Overall males and females exhibited similar trends in plasma vitellogenin, with the highest concentrations in spring of 2013 and 2015 (figure 2a and b) which were reduced by half starting in spring 2016.
- Prevalence of TO remained high throughout the study (figure 2c) and both TO prevalence and severity were highest in the spring and fall of 2016, corresponding with a high peak in atrazine (figure 3).
- Analysis of contaminant exposures during early development showed that TO development may have been affected by pesticide application within the immediate catchment.
- Peak concentrations of multiple chemicals contributed to the complex mixtures potentially affecting bass during the spring (spawning), early summer (early juvenile development) and fall (recrudescence)
Sources/Usage: Public Domain. View Media DetailsFigure 2. Annual and seasonal changes in plasma vitellogenin (Vtg) and hepatic vitellogenin (vtg) gene transcripts in A) female and B) male smallmouth bass. C) Prevalence and severity of testicular oocytes (TO) in male smallmouth bass.
The changes in the biological indicators were related to several factors:
- Multiple agriculture-related contaminants or land-use patterns were associated with TO, plasma vitellogenin, and gene transcript abundance in both male and female SMB. In males, positive associations between TO severity and pesticide application in the immediate catchment, plasma vitellogenin and total estrogenicity, and vitellogenin transcripts with high phytoestrogen cover crops were identified. In females, positive associations between plasma vitellogenin and the isoflavone, formononetin, and estrogen receptor transcripts (involved in vitellogenin production) with simazine and cholesterol were identified.
- The prevalence of TO and detectable levels of plasma vitellogenin and liver and testis vitellogenin transcripts were high throughout the study. However, vitellogenin, which is induced within hours to days (gene transcripts) and may persist for months (in plasma), did vary considerably by season and year (figure 2).
- Peaks of complex mixtures of numerous contaminants occurred during the spring/early summer when spawning and early development occurs and to a lesser extent in fall/winter during recrudescence.
Management and Research Applications
- This study identified numerous contaminants that will be considered for future laboratory exposure studies. This will help to identify cause and effect relationships between individual contaminants and biological changes associated with exposure which cannot be directly linked in wild fish.
- Based on the reproductive changes identified in females from this study, future research will also include gene transcript analysis from the ovary of female SMB.
- Land-use practices within the immediate and upstream catchments that may be associated with the release of these contaminants were identified and signify the importance of scale in monitoring studies.
For more information
- The results of this study were published in Ecotoxicology (with open access) at A case study: temporal trends of environmental stressors and reproductive health of smallmouth bass (Micropterus dolomieu) from a site in the Potomac River Watershed, Maryland, USA.
- Accompanying data release: Water chemistry and smallmouth bass biological data from the Potomac River, Dargan, Maryland, 2013-2019
- Blazer and others: Read a previous USGS summary of about intersex conditions include Land-use influences on estrogenic-endocrine disruption in fish within the Chesapeake Bay watershed
- Please contact Heather Walsh for more information at hwalsh@usgs.gov.