Land-use influences on estrogenic-endocrine disruption in fish within the Chesapeake Bay watershed

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Issue: Effects of exposure to estrogenic-chemical contaminants have been observed in many fish species worldwide. One effect is described as “intersex” because fish will take on characteristics of the other sex, such as immature eggs forming in male fish.

Studies in the Chesapeake Bay watershed have also identified the exposure of fish to endocrine-disrupting compounds. The estrogenic-endocrine disruption, and fish kills, have raised public and management concerns since sportfishing is of major economic interest, and rivers within the watershed provide numerous other ecological, recreational, cultural and economic benefits, as well as serving as a drinking water source for millions of people.

The Chesapeake Bay Program recognized these concerns and developed a goal for the Chesapeake Watershed agreement: Ensure that the Bay and its rivers are free of effects of toxic contaminants on living resources and human health. The research conducted by USGS and its partners has contributed to the Chesapeake Bay Program Toxic Contaminants Research Outcome to continually increase the understanding of impacts and mitigation options for toxic contaminants.

USGS Study: The USGS undertook an effort to summarize its previous research on estrogenic effects, which were conducted in collaboration with other federal and state management agencies. The objectives of the associated journal article were to:

  1. Summarize previously collected (2004 - 2010) published and unpublished information to document spatial and temporal observations of surface water estrogenicity (measured as estradiol equivalents) and indicators of estrogenic exposure (plasma vitellogenin and testicular oocytes) in black bass species,
  2. Identify landscape drivers of total surface water estrogenicity, plasma vitellogenin and testicular oocytes utilizing Classification And Regression Trees (CART) analysis,
  3. Establish baseline information that can assist in evaluating management and restoration activities, and
  4. Provide the science needed for a comprehensive understanding of sources and effects of estrogenic contaminants on fish populations.
Testicular oocytes

Figure 1

Some of the study considerations discussed in the journal article include:

  • Two indicators of fish exposure to estrogenic chemicals used in the study are testicular oocytes, a form of intersex (Figure 1), and vitellogenin (plasma, gene transcripts) in male fishes. Normally, estrogens induce vitellogenin production by the liver of egg-producing females. However, exposure to abnormal concentrations of natural or synthetic estrogens can also induce vitellogenin production by immature or male fishes.
  • Numerous focal studies documented the occurrence, severity, temporal and spatial variability of endocrine disruption in bass and estrogenicity in surface waters within the Bay watershed. The studies included findings from 5 major watersheds, including the Susquehanna, Potomac, Patuxent, James, and Rappahannock Rivers.
  • Data from these previous focal studies (Figure 2) were used in CART analyses to identify land-use associations and potential management practices that influence the occurrence of estrogenic endocrine disruption in bass.

Major findings:

Fish and estrogenicity sampling locations in the Chesapeake Bay river watersheds

Figure 2

  • Indications of estrogenic-endocrine disruption are widespread within the Chesapeake Bay watershed, with intersex or plasma vitellogenin being observed in all five major river systems sampled (above) More specifically:
    • Testicular oocytes were observed at 12 of the 14 sites at which largemouth bass were collected during June-Dec (considered the late season). Prevalence at the 12 sites ranged from 22 to 100%.
    • Sites sampled for smallmouth bass during the late season had individuals with testicular oocytes, ranging from 25 to 100%. During the early season (January to May) smallmouth bass were sampled at 20 sites with prevalence from 56 to 100%.
    • Previous studies including out-of-basin reference sites suggested background incidence of intersex in smallmouth bass is likely 10-14%.
  • Estrogenic exposure indicators were associated with urban and agricultural land-use characteristics. Based on CART analysis there were position relations estrogenic exposure indicators to agricultural land-use characteristics (percent cultivated land, pesticide application rates, percent of cover crops associated with phytoestrogen runoff), and developed land characteristics (population density, road density, impervious surface). There were negative associations for land use dominated by forest and shrubs.
  • Scale matters: Upstream and immediate catchment models differed emphasizing the importance of scale when considering the complex chemical mixtures and other stressors which can contribute to surface water estrogenicity and the associated adverse effects on fish.
  • Indicator choice matters: The indicators used represent different temporal exposures and response times. Estrogenicity is a measure of the estradiol equivalents at a specific point of time and can change rapidly. Male fish plasma vitellogenin is a response that takes hours to days to develop and circulating levels can persist for months after exposure. Testicular oocytes are most likely induced early in life with increased severity with repeated exposures. Consequently, temporal differences among indicators and responses can be expected.

Management Applications: This study provided a baseline and identified important considerations for ongoing restoration and management practices as they relate to reducing the effects of endocrine disruption in fish of the Chesapeake Bay watershed.

For more information:


Posted January 22, 2021


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