Many theories have been advanced to account for the increasing prevalence of autism in children, a disorder the Autism Society of America calls "the fastest-growing development disability" in the world. A CDC report in the June 2011 issue of Pediatrics reported that the percentage of children and teens in the US diagnosed with developmental disabilities such as autism has increased by 17 percent since the late 1990s. This upward trend of neurological impairment was also seen in the increased prevalence of attention deficit hyperactivity disorder as well as stuttering and learning disabilities.

While genes probably play a role, there is growing suspicion that EDCs are also involved in a range of neurological impairments, including autism.

Gore notes that autism is a complicated disorder and has no single cause. But, as with obesity and hormone-related cancers, she says, "the timing of autism's increase in the population also coincides with the rise of EDCs in the environment. We don't want to overinterpret the data, but the ways in which we've changed the environment appear to be changing how our brains develop. Low-dose exposures in early development are very important and very potent, but the problem is it is hard to detect them."

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For example, a large body of evidence from the Great Lakes and other areas links maternal polychloride byphenyl (PCB) exposure, largely from fish consumption by mothers during pregnancy, to lower IQs in children. One avenue by which PCBs are believed to do this damage is through thyroid disruption. Normal thyroid function is vital to proper neurological development.

"A loss of four or five IQ points may not seem like such a big deal," Gore says, "but when you consider the whole shift of the population's IQ because people are being exposed to these contaminants, there could potentially be a dumbing-down of the population."

Once used widely by industry for many purposes, including as a lubricant and coolant, PCBs were banned in 1979 because of environmental concerns. Made by combining benzene and chlorine, PCBs—which are classified as endocrine disrupters—sink to the bottoms of rivers and lakes. They enter aquatic plants and, when fish eat them, become part of the human food chain. When people consume them, they get stored in fat.

PCBs also aerosolize—meaning they break down over time and can turn into a fine, powdery substance carried by wind—and as a result are in virtually every body of water in the world, including the Potomac River. The EPA has issued a PCB advisory warning against the consumption of fish from the Potomac, especially of bottom feeders such as carp and catfish.

Scientific studies show that salmon raised in fish farms in the Atlantic Ocean have a heavier burden of PCBs than salmon caught in the wild—in part because farm-raised salmon don't swim as vigorously as those in the wild and as a result have more body fat. Although there are fewer PCBs in the environment than before, because of their long half-life they continue to pose a danger to humans, especially during early development.

The best way to prevent EDCs from entering Washington's drinking water would be to keep them out of the Potomac River in the first place. Tom Jacobus notes that the Potomac River Basin Drinking Water Source Protection Partnership was formed by area water utilities in 2004 to address this issue. Although the body has no enforcement powers, it's working with the Environmental Protection Agency and agricultural extension services in the states to raise awareness of the consequences of such practices as allowing cattle, especially those treated with hormones, to roam freely in tributaries. Efforts are also being made to convince cattle and chicken operations to control runoff into the river. Jacobus says the message is simple: "If you have a cattle-feeding operation that uses a lot of hormones, please don't let the cattle have access to the water, and control your runoff."

Jacobus says the best way to keep EDCs from the river is not to put them there in the first place. "I would also ask people not to throw your pills down the toilet and to look at labels on personal-care products and avoid those that may have EDCs in them." This is an important message but one unlikely to be heeded by most people.

Because there are hundreds if not thousands of chemical compounds, Jacobus says, water officials are trying to get a clearer understanding of the classes of chemicals and to regulate them: "We are looking at new and innovative treatment techniques, and within two years we will have treatment plans for some EDCs. We need to determine as an industry what these treatment levels should be, and we need to look at cost-effectiveness. Some of these EDC-removal technologies could cost $100 million. Ozone treatment, for example, works through electricity, so it's expensive to operate. We're not resisting this, but we don't want to get ahead of the science."

For now, Jacobus says, the Washington Aqueduct will continue to monitor the EDC issue. "We have a lot of confidence in the EPA, but at the same time we want to do better than EPA regulations because our customers want to us remove some of the unknown," he says. "We are also involved in a cooperative research project to understand more about endocrine-disrupting compounds and their role in drinking water.

"From the science we know now, we do not see a threat to drinking water at levels we can detect. But are we looking at it and thinking of future treatments? Yes, we are."

Contributing editor John Pekkanen has written about health and medicine for more than three decades. His September 2011 article, “Coming Back: Battling the Invisible Wounds of War,” about military servicemembers with brain injuries that would have been fatal in earlier times, can be found here.

This article appears in the July 2012 issue of The Washingtonian.