Environmental Endocrine Disruption Research


Endocrine systems regulate a wide range of physiological functions that are essential for health, homeostasis, adaptation, and the survival of animals, including humans.


to specific projects

-click here-

Worldwide, the occurrence of environmental endocrine disruption and therefore disruption of important health and physiological functions has been increasingly documented in animals, including both aquatic and terrestrial species, as well as humans.


Many human-derived contaminant chemicals have been identified as endocrine-disrupting compounds (EDCs).  These pollutants pose a potentially significant threat to health and well-being.

Surprisingly, studies of endocrine disruption in wildlife in California have been somewhat lacking, despite the obvious potential for impacts caused by enormous human populations and industry in the San Francisco region, Los Angeles/Orange County metropolis, San Diego region, and other urban centers such as Sacramento, Stockton, and Fresno, among others.

PCEC has engaged in scientific research that addresses these important problems since 2008.




With collaborators at several universities and agencies in both northern and southern California, the results of our research have uncovered several striking instances of endocrine-disrupted states in marine fish species exposed to environments such as locations recieving wastewater treatment plant (WWTP) output, urban river outlets, or contaminated sites. 

The Southern California Bight is the 'embayment' occurring between Point Conception in Santa Barbara down to San Diego County (indicated by yellow line).  This region represents one of the most significant interfaces between a marine environment and a tremendous human population.

From this work, important concepts have emerged: 

Environmental endocrine disruption is evident in a variety of different species, ranging from flatfish like English sole, to California scorpionfish, to surf perch.  The type and extent of endocrine disruption caused appears to be significantly affected by aspects of their life-histories, behavior, and diet. 

Environmental endocrine disruption is evident in different endocrine systems.  Disruption of the reproductive endocrine system (the most commonly studied example is estrogen effects) is only one avenue of impact.  In fact, significant disruptions of other endocrine systems are increasingly being identified in wildlife.  These disruptions cause altered regulation of growth, stress responses, defense/immune system, metabolism, and more.  An additional consideration -- possible interactions when different endocrine systems are altered simultaneously may mean additional physiological/health impacts than first expected.

There is ample evidence that many Pacific coastal environments are contaminated by a diversity of continuing and legacy pollutant chemicals (see overview here).  Measurements of different endocrine system components are increasingly being developed as biomarkers for different types of pollutant effects, as research shows that different types of contaminants affect different hormone systems differently.  The kinds of effects are often reflective of the types of pollutants present.

Quick-Links to

Selected Examples of

Environmental Endocrine Disruption

in the Pacific Coast Region:


Thyroid Endocrine Disruption Research Summary

In all vertebrate animals, thyroid hormones are critical for normal development and growth, and they have multiple other effects essential to a healthy physiology and survival generally.  Disruption of this endocrine system poses a significant concern for wildlife such as fish.  The objective of this research is to evaluate selected urban ocean and estuarine environments of California for the degree to which thyroid endocrine disruption is occurring in wild fish species and to understand the underlying mechanisms and causes.

This work initially identified and characterized a thyroid endocrine-disrupted condition in wild fish residing in San Francisco Bay (see our paper in the research journal, Aquatic Toxicology).  


Objectives in the continuing research include determining the possible environmental causes of this condition, elucidating the underlying mechanisms driving this condition, and evaluating the potential health (physiological) consequences such as impacts on growth.

Research Findings To Date

1.  The thyroid endocrine system exhibits significant alterations in fish residing in different San Francisco Bay locations.  The primary circulating thyroid hormone, thyroxine (commonly referred to as T4), is consistently reduced in fish from certain locations like Oakland Harbor (highly industrial) when compared with fish from other locations like Redwood City waterfront (less industrial).  The active thyroid hormone, triidothyronine (T3), also exhibits significant location-associated changes. 


While T4 is only made in the thyroid gland, T3 is mostly generated by conversion of T4 into T3 by "deiodinase" enzymes in other tissues (like liver).  The alterations in T4 and T3 indicate that some locations are associated with impaired thyroid gland synthesis of T4 while other locations are associated with impacts on deiodinase activity.  The latter suggests an important form of thyroid endocrine disruption that occurs outside of the thyroid gland.  . 

Blood plasma conentrations of thyroxine (T4) in fish sampled from different San Francisco Bay locations.  "PCBs" inside bar indicate that these locations have elevated concentrations of polychlorinated biphenyls (PCBs) in the environment.  Values shown are mean +/- standard error, with number of fish tested shown in parentheses at bottom of bar.

2.  To better understand the above findings, a field-based experimental approach was taken in which fish were tested for the ability of their thyroid to produce T4.  In these experiments, thyroid-disrupted fish from Oakland Inner Harbor were compared with reference fish at Redwood City that have normal thyroid function. 


Over two different years of study, it was consistently found that one of the fish species (shiner perch) exhibited significantly impaired thyroid gland capacity to produce T4, pointing to the thyroid gland as a target of the environmental effect (e.g., by an endocrine-disrupting chemical, or EDC).  Interestingly, when examined under a microscope, the cells and structure of thyroid tissue are not normal in the impaired fish (see picture below).  In a second fish species, Pacific staghorn sculpin, this type of impairment was not evident, yet another aspect of the thyroid system appeared to be impacted (see #3 below).

Thyroid Histophysiol-SF_Lee_2013_full.jp

Histological examination of thyroid tissue sampled from a healthy fish (left-side panels) and a thyroid-disrupted fish (right-side panels). The results of this work indicates impairment of the cellular make up  and structure of the thyroid tissues in thyroid-disrupted fish.

(upper panels are analyzed using a different staining technique as compared with the lower panels).

3.  A method was established to measure liver 5’-deiodinase activity and used to assess whether thyroid endocrine system disruptions may be related to changes in this important enzyme system that operates outside of the thyroid gland.  In Pacific Staghorn Sculpin residing in Oakland Inner Harbor, liver 5’-deiodinase activity was significantly depressed, which was correlated with reduced T3/T4 ratios. Thus, in the sculpin, environmental effects on peripheral deiodinase activity may be driving thyroid disruptions leading to reduced T3 levels.


T3/T4 ratio was highly correlated with hepatic 5’-deiodinase activity, indicating that measurement of T3 and T4 in plasma (and calculation of T3/T4) serves as an indicator that peripheral deiodinase status may be impacted in fish.

4.  It was also determined that hepatic 5’-deiodinase activity was significantly related to environmental chlordane* exposures in fish, in accordance with earlier findings that thyroid hormones, and especially T3/T4 ratio, are positively correlated with tissue chlordane concentrations.  There was also an overall relationship between deiodinase and environmental PCB** exposures.  These findings point to both classes of chemicals as thyroid-disruptive agents, likely acting through impacts on peripheral deiodinases.


in aquatic environments

are derived from Chlorinated Pesticide use

and are present in San Francisco Bay

**Polychlorinated Biphenyls (PCBs)

in aquatic environments

are derived from old electrical equipment

and are present in San Franciso Bay.

5.  Abnormal thyroid status is well known to impact growth and development in all vertebrates including fish.  Our research indicates that the principal growth-regulatory hormone, called IGF-I, also shows environment-related alteration, including reduced IGF-I in thyroid-disrupted fish from Oakland Inner Harbor.  Reductions in IGF-I were also significantly correlated with tissue exposures to PCBs and chlordanes (similar to thyroid hormones).  In addition, in one of the species (sculpin), thyroid endocrine status was significantly related to IGF-I levels, pointing to a functional link to the important growth system.

Conclusions and Implications To Date

The findings to date indicate that wild fish residing in different inshore environments of San Francisco Bay are exhibiting significant alterations in their thyroid endocrine systems.  This has been observed over several years of work.  It is also notable that two different fish species representing distinct life histories exhibited a number of similar alterations at the same study locations, although some differences are also evident.


This work confirms that 'current-day' exposures to specific kinds of contaminant chemicals are significantly related to endocrine disruption in wild fishes.   Alterations in thyroid system components were related to exposure to PCBs and chlorinated pesticides (chlordanes).  Sublethal effects of contaminant chemicals, particularly through endocrine disruption mechanisms, have strong potential to cause impairments and reduced physiological `performance in wild life.   

 The scientific approaches undertaken through this work point to the potential value of screening methodologies, such as endocrine or biomarker measurements, to assess environmental/water quality effects in fish and wildlife.  Strengthening our understanding of the links between different types of environmental contaminants, endocrine disruption effects, and associated phenotypic impacts, are critical in continuing to validate these approaches and ultimately in establishing effective thresholds for different types of contaminants.  

Overall, the results have provided evidence indicating that the thyroid endocrine system is significantly, sometimes substantially, disrupted in fish residing in different locations in San Francisco Bay.  Importantly, these effects appear to be related to exposure to specific classes of contaminant chemicals persisting in the environment.  Specific components of the thyroid endocrine system are altered, leading to altered thyroid hormone levels, which may be transduced into changes in growth regulatory systems.

Adrenal Endocrine Disruption Research - Summary


One form of the endocrine disruption is not widely known, but could pose significant risks to wildlife.  Our work in both northern and southern California marine and estuarine environments show that it may be related to “urban ocean” polluted settings.

This disruption occurs within the endocrine system responsible for generating the steroid hormone, cortisol.  This steroid hormone is synthesized and released by the adrenal gland (in fish, this gland is referred to as interrenal tissue). 

Disruption of cortisol in any vertebrate, including you! or a fish, has strong potential to cause health impairments relating to metabolism, defense (immune), growth, and stress responses.  Importantly, a normal bodily response to stress depends on a robust increase in the synthesis and release of cortisol and its actions that facilitate adaptation to stressors in the environment.

inside info...

Cortisol is elevated in a variety of stressful situations encountered by fishes, such as life-threatening circumstances, social stress, crowding, water quality (contaminant chemicals), and others.  Cortisol then exerts important metabolic actions, particularly the mobilization of fuels (e.g., liver glucose release) to meet the increased energy demands associated with adapting to stress.  Cortisol also inhibits energy-expensive physiological functions, including somatic growth, defense and immune function, and reproduction, among others, as part of its role in re-directing energy toward dealing with stressor(s). In addition to cortisol’s essential role in stress responses and adaptation, it is also important in “day-to-day” homeostatic control of metabolism and many other physiological systems. 

In collaborative efforts with the Orange County Sanitation District (OCSD) in southern California, wild marine fishes residing in locations offshore of urban areas have been found to exhibit significant impairments in cortisol responsiveness.

As illustrated below, average “stress-induced” cortisol levels are greater than 200 ng/ml in English sole sampled from reference locations (less impacted areas).  In contrast, fish sampled offshore of "urban-impacted" areas (like WWTP outfall sites) are incapable of producing even half that level of cortisol under identical stress conditions (asterisks indicate statistical significance at p<0.001).  Our studies of other marine fish like hornyhead turbot and California Scorpionfish, as well as fish from impacted sites in northern California (San Francisco Bay), like Pacific staghorn sculpin and shiner perch, all exhibit impaired cortisol responses in association with contaminated environments.

final_English sole Cort disrupt 4-2020.j

Therefore, active factors ( e.g., pollutants) appear to be present in urban coastal environments that appear to induce this form of endocrine disruption.

We continue to research the mechanisms underlying and occurring in this disruption:


  • What kinds of specific chemicals might be causing this condition?

  • In what part(s) of the cortisol endocrine system are there impacts?

  • What kinds of physiological health problems might arise due to this condition?

Some research not shown here points to significant effects on gene expression that is essential to normal cortisol synthetic response.  The work aims to determine what specific molecular components underlie the observed endocrine disruption.


Other work not highlighted here indicates that cortisol endocrine disruption may be associated with impacts on growth, as endocrine regulators of growth like IGF-I are altered.

Yet other work indicates that cortisol endocrine disruption may lead to problems in defense physiology, as fish with impaired cortisol production exhibit much higher levels of parasitism.  Click HERE to find out more about this.


Environmental Disruption of the Reproductive Endocrine System?


In the early 2000s, Jesus Reyes working with collaborators at California State University Long Beach discovered that males of an indigenous flatfish species in southern California had consistently very high blood concentrations of the female sex steroid, 17β‐estradiol, in contrast to several other regional flatfish species (Reyes, 2006).  In response to these findings, follow-up research was initiated, in addition to a large region-wide collaboration of both university and government agency participants.  The work was directed at understanding the possible relationships between the occurrence of human-derived contaminants and biological effects like high estrogen in males and possible feminization. 

The reproductive endocrinology of the hornyhead turbot (Pleuronichthys verticalis) was characterized by comparing groups sampled from different coastal study sites representing varying degrees of pollution, in order to try to screen for potential endocrine disruptive effects. Turbot were sampled from locations near the coastal discharge sites of four large municipal wastewater treatment plants (WWTPs) located between Los Angeles and San Diego, California, USA, and were compared with fish sampled from three far‐field reference locations in the region.

The findings indicated environmental presence of both "legacy" contaminants (e.g., DDTs, PCBs) and "contaminants of emerging concern" (e.g., pesticides, pharmaceuticals), and many of these chemicals were measured in fish tissues.

Seasonal reproductive cycles were observed at all study sites.  Sex steroids (17β‐estradiol, testosterone, 11‐ketotestosterone) peaked in the spring and were low in the fall, and these changes corresponded to similarly timed gonadal changes and plasma vitellogenin concentrations in females (vitellogenin is egg yolk protein important in making eggs).  All through this work, the males consistently had "female levels" of estradiol in their blood.

Comparison of fish from the different study sites demonstrated some regional differences in plasma levels of hormones, indicative of location‐associated effects on the reproductive endocrine system of the fish.  While such differences could not be linked to the ocean discharge locations of the four large wastewater treatment plants, it appears that some unknown environmental 'actor' (endocrine disrupting chemical??) could play a role in this species' reproductive system that, among other aspects, results in males with extraordinary estrogen levels. 

These findings have led to a number of follow-up projects aimed at understanding the reproductive biology of this fish and the nature of this potential environmental effect.

 The graphic below shows the difference between a male English sole (yellow bars) and male hornyhead turbot (pink bars).  Male English sole have relatively low blood levels of estradiol in their blood, which is expected for males generally, whereas male hornyhead turbot have extraordinary levels of estradiol.  Consistent species differences are seen in testicular expression of a key enzyme, P450 aromatase, that results in conversion of testosterone into estradiol. 

What is the reason for this elevated enzyme in testicular tissue?

See our papers and others that address this research