Pollution may be altering levels of the sex hormones estrogen and testosterone in fish found in U.S. waterways, including two in the Bay watershed, according to a report by the U.S. Geological Survey, which examined fish in 25 streams nationwide.
The national "reconnaissance study" is the broadest investigation to date of the potential for endocrine disruption in fish. The endocrine system produces hormones which regulate important bodily functions, such as growth, development, reproduction and behavior.
Interest has grown in recent years over a variety of pollutants - including DDT, PCBs, dioxins, some widely used herbicides, plasticizers and others - may mimic or block endocrine system processes, potentially affecting critical bodily functions.
The study focused on carp, a bottom-dwelling fish whose feeding habits expose them to contaminants found in the water, sediments and food.
In releasing the report, USGS officials stressed that their study only looked for evidence of endocrine system disruptions. The study did not examine whether any apparent endocrine system disruptions were actually affecting fish.
"Since altered sex hormones may cause reproductive impairment, we need to follow up this reconnaissance study with detailed assessments of fish reproduction at selected sites," said Steve Goodbred, USGS research scientist and senior author of the report.
The study analyzed more than 600 fish collected from streams in 13 states and the District of Columbia that contained a range of land uses and varying degrees of contamination. In the Bay watershed, samples were taken from the urbanized Anacostia River near the Washington Ship Channel in the District of Columbia, and in Shenandoah River at Millville, W. Va., a watershed dominated by cropland and forest.
The results showed significant differences in sex hormones and vitellogenin, an estrogen-controlled protein necessary for egg development in fish and birds. Although the USGS reported that some of those differences probably resulted from natural variability, it also said some site-to-site differences in the hormones appeared to be associated with contaminants.
"The finding of a correlation between hormone levels and contaminant levels in fish from such diverse locations is both a cause for concern and a call for further study," USGS Director Dr. Gordon Eaton said in a statement that accompanied the release of the study.
The contaminants that were significantly correlated with hormones were pesticides in water, phenol compounds in streambed sediments, and organochlorine compounds in biological tissues. But the USGS said it is not yet possible to pinpoint specific contaminants or factors that may be related to significant differences in fish hormones.
The study examined sperm production in male fish and found that most fish had moderate or high levels of production. But 86 percent of the fish from the Shenandoah and Anacostia rivers had low rates, though the study said that may have occurred because samples in those rivers were taken late in the year.
One of the male fish taken at the West Virginia site had abnormal gonad conditions which the report said was similar to those which may be attributed to sex-steroid hormone levels. It was the only fish in the study that had physical abnormalities which might be linked to endocrine system disruption.
The report said the West Virginia site could be considered a "contaminated site" for further work, based both on the sampling of fish taken during this study and the availability of historical fish data and reference sites.
The study was a collaborative effort among the USGS, the National Biological Service (now the Biological Resources Division of the USGS), and the University of Florida's Biotechnologies for the Ecological, Evolutionary, and Conservation Sciences Program.
Most of the sites sampled are established water-quality sites of the National Water Quality Assessment (NAWQA) program, a major USGS initiative responsible for assessing the levels and distribution of contaminants in the nation's water resources.
The report is available on the World Wide Web at http://water.wr.usgs.gov
Interest in Endocrine Disruption Has Risen
Interest in endocrine disruption - the effects of environmental contaminants on the endocrine system of animals - has increased markedly over the past 20 years. ... At least 45 chemicals have been identified as potential endocrine-disrupting contaminants, including industrial contaminants (such as dioxins and polychlorinated biphenyls [PCBs]), insecticides (such as DDT and carbaryl) and herbicides (such as dichlorophenoxy acetic acid [2,4D] and atrazine).
Injury to endocrine function by environmental contaminants is potentially debilitating to a variety of physiological systems. The endocrine system in animals consists of glands that produce hormones that enter the bloodstream to maintain physiological homeostasis. This is accomplished through regulation of immune, metabolic, morphogenic, neural and reproductive functions. Previous studies have found correlations between specific impairments of reproductive activity and elevated tissue concentrations of xenobiotic agents. The reproductive injuries reported to date include reduced fertility, hatchability and viability of offspring; impaired reproductive hormone activity; and altered sexual development and behavior. There are also reports of slow growth, atrophy and lower rates of metabolic activity.
- U.S. Geological Survey