Put bluntly, the problem is poop. Fecal pollution--mainly from raw sewage--is contaminating large stretches of recreational water from the Gulf Coast to the Great Lakes.
Swimming in unsafe water can lead to sore throats and diarrhea, as well as more serious illnesses like meningitis and severe gastroenteritis. Recent research has shown that, after many years of decline, death rates from microbial gastrointestinal illness are on the rise. ¿Recreational exposures clearly play a role in causing these illnesses," says epidemiologist Rebecca Calderon of the U.S. Environmental Protection Agency.
Pollution caused more than 12,000 beach closings and advisories in 2002--the second highest number in 13 years--according to a study by the Natural Resources Defense Council. (The 2001 numbers were slightly higher, mostly because of drought conditions in 2002.) The continual rise in ¿no-swimming" days in part reflects better testing standards, the report notes, but scientists disagree over how to best monitor pollution and warn swimmers.
For years, the standard analysis has been based on coliforms--bacteria that give an estimate of the amount of feces in a sample. Most officials take one water sample a day and then post a warning sign on the beach when bacteria levels exceed a specified value.
¿It's a flawed system," observes Mark Sobsey, an environmental microbiologist at the University of North Carolina at Chapel Hill. Since bacteria must be grown, an analysis can take 24 hours or more. ¿We are still in this dilemma of making decisions about water that has already come and gone," he remarks.
To assist state and local officials with monitoring programs, the EPA introduced the Beaches Environmental Assessment and Coastal Health (BEACH) Act in October 2000. One goal of the BEACH Act was to spur development of ¿rapid indicators" to measure water quality on an almost continuous basis. ¿Obviously, people would like it to be done 10 seconds or less, but we thought that was pretty unrealistic," says Al Dufour of EPA's National Exposure Research Laboratory. ¿There was an arbitrary goal set up: We were going to attempt to measure water quality in two hours or less."
A number of new technologies that meet this standard are now being tested in various environments, and most experts agree they are a step in the right direction. But recent research suggests that rapid indicators might not be a panacea.
Stanley Grant of the University of California at Irvine has analyzed warning errors at Huntington Beach, Calif. His findings, published the May 1 issue of Environmental Science & Technology, suggest that even if sample turnaround were almost instantaneous, error rates in beach warnings would still be quite high. Grant's work points to a more fundamental problem: the current ¿binary" advisory scheme--wherein a warning sign is either posted or not, giving the public no further information--is intrinsically error prone, he asserts. He recommends switching to an ¿analog" system, similar to the one used to issue ozone warnings in urban areas, assigning a letter grade to beaches from "A" to "F."
Other researchers maintain faith in rapid indicators. Stephen Weisberg, executive director of the Southern California Coastal Water Research Project, agrees with Grant that if officials are taking only one sample each day, then decreasing sampling time will do little good. ¿But if you sample once in the morning, then get the results right away and find out you have a high level, you can sample again five times in different places before noon," he counters. Weisberg and Sobsey were among the experts on the committee for a recent National Research Council (NRC) report that addressed indicators of waterborne disease. The report stressed the importance of rapid indicators but placed them in the context of a three-phase approach to monitoring beaches.
The first phase is simply an early warning, attainable through fast and cheap pollution detection techniques. ¿You don't need a lot of specificity," Weisberg explains. ¿You can have some false positives, but what you don't want is a lot of false negatives." A false negative means people are swimming in polluted water.
Phase two of the NRC framework--confirmation--requires a larger set of tools to put the problem in a public risk context. ¿Invariably, that means human health or epidemiological studies, where you quantify the risk of people becoming ill from swimming," Sobsey says. He advocates following the lead of European scientists, citing a study conducted by British researchers from the 1990s in which they made a grid in the water and sampled continually for days, simultaneously measuring water quality and exposure levels for specific swimmers.
The EPA is now conducting just such a study in collaboration with the Centers for Disease Control and Prevention, Calderon reports. The National Epidemiological and Environmental Assessment of Recreational (NEEAR) Water Study is combining data from rapid indicators with beachgoer interviews to get a clearer picture of the link between water quality and human health. So far researchers have studied two freshwater beaches on Lake Michigan and Lake Erie, but the data await analysis.
In the third and final phase of the NRC framework, the emphasis shifts to ascertaining what caused the problem and how it can be fixed. This phase requires that investigators use genetic techniques to distinguish human and animal sources, which can indicate different pollution sources. If, for example, a human source is detected, it is most likely from a leaky sewer pipe, Weisberg notes. Pinpointing the source is also important because it is possible, although not well established, that animal feces are less virulent than human feces. ¿Not that we're saying you want to swim in bird poop," Wesiberg says. ¿But in the longer term, we may be in a position to set different standards and adjust our warning systems." Tools that quickly differentiate between human and animal sources using complex libraries of genetic information are still years away. A simpler method, however, might be to test the samples for viruses rather than sequencing DNA from source organisms. Finding a human virus would automatically rule out an animal source, Dufour explains.
A detailed understanding of contamination sources could also pave the way for models that forecast pollution events. Grant's study this past spring noted that pollution levels at Huntington Beach were consistently higher at high tide, and rain has long been considered a good predictor of troubled ocean waters. ¿The numbers almost invariably go up dramatically when it rains," Sobsey says, because storms tend to overwhelm sewage systems.
The EPA has put together a small group of researchers to develop a forecasting system aimed at keeping officials a day ahead of problems. ¿This [would be] far better than the 'I can tell you tomorrow what you swam in today' scenario we are in," Calderon asserts. But is an accurate forecasting system really just a pipe dream? Dufour says no: ¿After all, just think about the weathermen; they're getting better all the time."
Jason Gorss is based in upstate New York.