Back at the lab, Blazer and her colleagues examined fish tissue microscopically and discovered that some bass had bacterial infections while others had fungal infections and still others were afflicted with parasites. This finding led her to conclude that the plague killing the fish wasn't a toxin, a bacterium, or any single agent but resulted from immune suppression that permitted opportunistic infections to flourish and kill the fish.
"I think the fish kills were caused by the same chemicals in the river water that are inducing intersex," Blazer says. "Besides leading to intersex, exposure to these chemicals, particularly estrogenic hormones, depresses the immune system. The intersex occurs when the fish are exposed to these estrogenic compounds at a young age."
The study found that even bass with no signs of intersex contained detectable levels of at least one endocrine-disrupting compound.
Based on a USGS study published in Fish & Shellfish Immunology in 2009, it appears that estrogenic compounds can lower levels of hepcidin, an iron-regulation hormone found in mammals (including humans), amphibians, and fish. Researchers believe hepcidin acts as a first line of defense against certain disease-causing bacteria, viruses, and fungi, which could explain why intersex fish and the fish kills occurred at the same time.
Blazer and her colleagues published their findings in 2007 in the Journal of Aquatic Animal Health. The report concluded that intersex fish were "an important indicator of potential endocrine disruption."
What About Bottled Water?
As with tap water, where it comes from and how it's processed are key. Read more.
Blazer has found intersex fish on both the lower and upper branches of the Potomac and on both forks of the Shenandoah. She says the fish kills and intersex are most prevalent along the most agricultural areas of the rivers—where dairy, cattle, and poultry businesses reside—but that those are probably not the only sources of the chemical soup that kills fish.
Kelble says he saw the highest mortality in the upper reaches of the Shenandoah, which are close to the highest-intensity animal-feeding operations. The nine-county Shenandoah Valley has more than 900 poultry farms, with more than 87 million chickens in Rockingham County alone. On several occasions, Kelble and others have seen cattle herds wading in tributaries of the Shenandoah. The residue of human and animal excrement, which holds both natural and manmade chemicals, is considered a significant source of EDCs. The USGS reported that a higher incidence of intersex fish occurred in streams that drain areas with intensive agricultural production and high human population when compared with non-agricultural and undeveloped areas.
Blazer also has found intersex fish in the Conococheague Creek and the Monocacy River in Maryland. She believes the intersex fish are the result of a "toxic soup" of endocrine-disrupting compounds that are finding their way into the Shenandoah and Potomac rivers. This mixture comes from homes, farms, and industry and has been added to the water for years. When it reached critical mass, tens of thousands of fish died.
So what do dead fish 200 miles upstream from Washington have to do with the quality of water we drink?
EDCs are a broad class of molecules that the EPA defines as natural or synthetic agents that interfere with "natural blood-borne hormones that are present in the body and are responsible for homeostasis, reproduction, and developmental process."
Natural hormones are secreted by endocrine glands into the bloodstream and bind with specific cell receptors. Once bound, the receptor carries out the hormone's instructions, either modifying existing proteins or directing the cell's DNA to produce specific proteins. Because EDCs mimic natural hormones and interfere with the endocrine system, they can adversely affect normal growth, cognitive function, metabolism, and reproduction in animals and humans.
Measuring their risk to human health has been hard because they interact in complex ways at minute concentrations, both alone and in combination with one another.
How they act in combination remains unclear. EDCs have been in the environment in one form or another for more than 50 years and are present in hundreds of millions of people worldwide. At last count, more than 80,000 synthetic chemicals, mostly derived from petroleum and vegetable sources, are in use today. The process of making these synthetics involves toxic catalysts and reagents. Few of these 80,000 chemicals have been tested to determine what effect they have on humans.
Individuals respond to EDCs in different ways, but one thing is clear: Never before have humans had so many diverse synthetic chemicals assaulting their bodies, a phenomenon some observers have called "the largest uncontrolled science experiment in history."
EDCs are present in many household items, such as preservatives, plastics, cosmetics, and antibacterial soaps that contain triclocarban, an endocrine disrupter that is flushed into wastewater and ultimately into the river. Scented soaps and shampoos, hair-coloring agents, skin creams, and sunscreen lotions contain them, as do some spermicides, toilet papers, and facial tissues.
They're also found in birth-control pills, hormone-replacement therapies, and androgen-blocking or androgen-enhancing agents. Chemotherapy and thyroid medications, antibiotics, and other prescription drugs, some of which contain EDCs, enter the environment when they're excreted into wastewater and flushed down the toilet. Pharmaceuticals can enter the water supply directly when unused pills are thrown away.
In 2008, the Associated Press published a series of stories entitled "Pharmaceuticals Found in Drinking Water." The AP conducted a survey of water quality and found that pharmaceuticals were present in the water systems of two dozen major metropolitan areas. Washington's drinking water contained evidence of six drugs, including carbamazepine (an antiseizure medication), monensin (an antibiotic used in animal feeds), sulfamethoxazole (an antibiotic often given for ear infections), ibuprofen (Motrin and Advil), naproxen (Aleve), and caffeine. Philadelphia's drinking water contained evidence of 56 drugs and byproducts. The AP estimated that the health-care industry flushes 250 million pounds of drug waste down drains each year.
In tests conducted by the USGS between 2003 and 2005, trace amounts of 26 chemical compounds were detected in Potomac River water, including the herbicide 2,4-D, a component of Agent Orange, and insecticides including DEET. Atrazine, a chemical commonly used in weed killers, has been associated with intersex in amphibians and has been found in many rivers, including the Potomac. Studies revealed that male frogs exposed to atrazine produce eggs in their testes, the same phenomenon seen with intersex fish.