By Hannah Hoag
Chemicals flushing into sewer systems have been in the news for years. From opiates and hormones to heart medications, studies have detected a range of pollutants. Tests of sewage from hospitals have uncovered antibiotics, and investigations of sewage systems have exposed widespread illicit drug use in cities worldwide.
But now a group of water-management scientists claim that some of these studies may be making exaggerated claims, producing dramatic variation in concentration estimates or not detecting substances because of fundamental flaws in sampling protocols.
Christoph Ort, an environmental engineer at the University of Queensland in Brisbane, Australia, and his colleagues looked at 87 peer-reviewed journal articles that investigated the fate of pharmaceuticals, illicit drugs and personal-care products such as cosmetics. The articles, published online July 26 in Environmental Science & Technology, quantified the concentrations or fluxes of these compounds based on samples taken from sewers.
"There can be cases where you really get the wrong conclusions," says Ort. Less than 5 percent of the studies offered a proper analysis of the system under investigation, and they didn't take into account sewer type, substance and source when setting up their sampling methods, he says.
Mosaic of discharges
Rather than suggesting that there isn't a problem with pharmaceuticals and other substances in waste water, the review questions the legitimacy of the assigned values.
Ort hopes that the review leads scientists to scrutinize their methods. "I really think it is ignorance. I'm not accusing anyone of doing it on purpose," he says.
Although the sewage en route to a treatment plant may seem to be a continuous foul-smelling stream, it is in fact a mosaic of wastewater pulses discharged from toilets, dishwashers, hospitals and industries.
"The study is a wake-up call," says Chris Metcalfe, an environmental scientist at Trent University in Peterborough, Ontario, who has analyzed -blocker drugs in sludge and waste water in Canada and Germany. "It's the kind of thing that analytical chemists will read and say, 'Maybe we need to clean up our act a little bit in terms of not only designing our sampling schemes but also how we interpret our data and the limitations of the data we're collecting'."
Although some will see the review as a swipe at the literature and those behind it, Ort chose not to point fingers at any single paper included in the analysis. Instead, he and his colleagues demonstrated the sampling risks in an accompanying study of pharmaceuticals in two different sewer systems using a variety of sampling methods. The magnitude of the sampling artifacts ranged from not significant to more than 100 percent.
Ort and co-author Michael Lawrence, now at the Department of Environment and Resource Management in Queensland, had previously questioned the behavior of gadolinium, a medical-imaging contrast agent, during wastewater collection and treatment because they deemed the field sampling strategy to be lacking.
"Sampling becomes more of an issue for compounds that aren't as widely used," says Patrick Phillips, a hydrologist at the United States Geological Survey in Troy, N.Y. A daily "grab sample"-- dunking a bottle into a sewage stream for little more than a second--can fail to detect peaks and underestimate concentration.
Focus on reproducibility
Environmental chemists used to look for the presence of personal-care products in wastewaters. However, it is now more important to quantify those substances to understand their environmental flux, the options for controlling their entry into the system and their removal by sewage treatment plants. They can also help reveal the number of drug users in a catchment area, facilitating public-health planning.
"The issue that Christoph studies is an important one, especially if one is trying to make decisions about what wastewater data means," says Jennifer Field, an environmental chemist at Oregon State University in Corvallis, who is currently collaborating with Ort on a study of illicit drugs in waste water.
"If we're getting to the point where the wastewater treatment plant is going to spend millions of dollars to put in a technology, we need to have data that's as accurate as possible to let them know how the technology will benefit them," says Metcalfe.
Although he's pained by the current situation, Ort says it can be fixed. "If only a small fraction of the effort that is being put into the analytical chemistry is put into understanding the potential dynamics in sewers and developing the sampling, we would not have this problem," he says.
"Taking a representative sample and quantifying full-scale environmental flows is an extremely challenging task," says Ort. "But researchers should not only rely on luck, but on reproducibility."