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Endocrine Disrupters Study
The endocrine system consists of various glands located throughout the body, which synthesize and secrete hormones that regulate essential biological processes including development, growth, metabolism and reproduction. Recently, it has been discovered that a variety of environmental pollutants, termed endocrine disrupters or endocrine disrupting (EDCs) can alter the function of the endocrine system causing adverse health effects in an organism or its progeny. Chemicals currently identified as endocrine disrupters (Table 1 and Figure 1) include certain alkylphenol polyethoxylates (surfactants), bisphenol-A (monomer of polycarbonate), PAHs, pesticides, PCBs, dioxins, organotins and some synthetic hormones. The ability of an EDC to affect an individual or population in the aquatic environment is likely to depend on a number of factors, including the potency or efficacy of the EDC, its concentration, duration of exposure, bioconcentration potential, presence of other EDCs, life stage exposed, season, other environmental stressors present (e.g., temperature, salinity, and other contaminants), and mobility of the individual.
Chemicals that can either mimic or antagonize endogenous hormones such as the estrogens or androgens could potentially have serious effects not only on the development and well being of an individual organism, but perhaps more importantly on the ability of that organism to reproduce, and its offspring to survive and reproduce. Investigations to identify the types and impacts of EDCs in the laboratory and in the field have become an important area of research, with implications not only for environmental health but also human health.
Much of the environmental endocrine disrupter work has involved fish due to similarities in their endocrine system to higher vertebrates, a demonstrated sensitivity to EDCs, and the discovery of apparent endocrine disruption in wild fish from a number of locations. To address the concerns raised by EDCs in the aquatic environment, NOAA's NS&T Program recently completed a project to review documented effects in both salt and freshwater species of fish, and to investigate possible reproductive endocrine disruption in a killifish in the Chesapeake Bay.
Assessment of Endocrine Disruption in Salt and Freshwater Species of Fish
Approximately 140 research articles were reviewed as part of the assessment. Most of the investigations to date involving fish have concentrated on reproductive endocrine disruption. Laboratory studies have revealed that a variety of chemicals from certain industrial intermediates to PAHs can interfere with the endocrine system in fish. The potency of most of these chemicals, however, is typically hundreds to thousands of times less than that of the endogenous hormones. Evidence of endocrine disruption in fish in the environment ranges from the presence of the female egg protein vitellogenin in males, and reduced levels of endogenous hormones in both males and females, to gonadal histopathologies and even intersex individuals. In female fish, vitellogenin occurs naturally, with concentrations varying with the reproductive cycle. Elevated vitellogenin levels in male fish have been used as an indicator or biomarker of exposure to estrogens or to estrogenic compounds in the environment.
Results from the assessment, however, indicate that overt endocrine disruption does not appear to be a ubiquitous environmental phenomenon in fish, but rather more likely to occur near three types of land use activities, including sewage treatment plants, pulp and paper mills, and in areas of concentrated industrial activities with high levels of organic chemical contamination. Some of the most severe examples of endocrine disruption in freshwater (Table 2) and saltwater (Table 3) species of fish have been found adjacent to sewage treatment plants, with effects ranging from the presence of vitellogenin in males to an intersex condition in which testicular and ovarian gonadal tissue are both present in the gonad of a normally separate sex species. Effects are thought to be caused primarily by natural and synthetic estrogens and to a lesser extent by the degradation products of alkylphenol polyethoxylate surfactants. Effects found in fish near pulp and paper mills include reduced levels of estrogens and androgens as well as masculinization of females, and have been linked to the presence of b-sitosterol, a plant sterol. Effects seen in areas of heavy industrial activity typically include depressed levels of estrogens and androgens as well as reduced gonadal growth, and may be linked to the presence of PAHs, PCBs, and possibly dioxins. Although effects, some severe have been seen in some areas, at this time there is no clear indication that large populations of fish are being seriously impacted as a result of endocrine disruption, although additional work is needed to address this possibility.
Chesapeake Bay Study
As part of the project, a limited survey and laboratory study involving personnel from NOAA and the University of Maryland was completed in selected tributaries of the Chesapeake Bay, to assess possible reproductive endocrine disruption in the killifish Fundulus heteroclitus (Figure 2). Seven field sites (Figure 3) representing a variety of land use activities ranging from relatively pristine to industrialized areas near Baltimore were established.
Male and female fish were sampled during the fall months after reproduction had ceased, and again in the spring/summer, the peak reproductive period for this species, for a period of 2 years. All spring/summer sampling occurred within 2 days of the full moon to coincide with the species' lunar spawning cycle. Parameters measured included plasma vitellogenin, as well as certain gonadal and hepatic indices along with some gonadal histologic analysis. Vitellogenin was analyzed by direct ELISA using a monoclonal antibody prepared by the University of Florida.
The results of the plasma vitellogenin analysis in males are shown in Table 4. Eighty-six percent of the male fish sampled, however, contained no detectable vitellogenin as determined by the ELISA. In all cases except one, levels of vitellogenin were low, in the range of 0.01 - 0.09 mg/ml. As a comparison, reproductive female F. heteroclitus typically contain between 12 and 16 mg/ml plasma vitellogenin. There were no significant differences in vitellogenin concentrations in males between sites, and there were occasional positive detections of vitellogenin in males from the pristine sites.
A second species of fish, the sheepshead minnow (Cyprinodon variegatus) was also collected at three sites where F. heteroclitus was taken (reference and two contaminated sites). An analysis of vitellogenin in male sheepshead minnows revealed no significant difference in vitellogenin levels compared with F. heteroclitus.
Although there were no apparent estrogenic effects, there was some evidence of antiestrogenic and antiandrogenic effects at certain sites. The gonadal index in male and female fish from Baltimore, for example, was significantly lower than fish from the reference site. Additionally, females from Baltimore had vitellogenin levels significantly lower than the reference site. Data on sediment contaminant concentrations for the Baltimore locations as well as a reference site were obtained from published databases. An analysis of the data revealed that lower vitellogenin levels and gonadal indices in female F. heteroclitus were negatively and significantly correlated with sediment PAH concentrations, and lower gonadal indices in males were negatively correlated with sediment concentrations of PAHs and PCBs. Histologic examination of gonadal sections, however, failed to reveal any ovotestes in the fish examined, and also failed to reveal any major differences in gonadal measurements made on fish between sites.
For more information on the project, or to request a copy of the report entitled, "Endocrine Disruption in Fish: An Assessment of Recent
Research and Results", please contact:
Tony Pait
301-713-3028 x 158
tony.pait@noaa.gov