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BOMB-MAKERS or chemists with Breaking Bad crystal-meth labs better watch out. A sewer system full of chemical sensors could sniff out their homemade labs as part of a €4.5 million European Union-funded research programme called Emphasis.
The idea is that once a sewer sensor finds telltale traces of home-brewed explosives, it sounds an alarm and a police team carrying a portable, high-resolution sensing unit can be dispatched to narrow the search and pinpoint the exact location. The technique could also be modified to look for signs of illegal drug factories.
Emphasis is led by Hans Önnerud, an analytical chemist with the Swedish Defence Research Agency in Kista, north of Stockholm. His approach relies on the fact that some liquids and gases from bomb or drug production will leak into the sewers through sinks, baths or toilets, and into the air of a city via windows and skylights. He says a hint that such gases might be detectable became clear in the wake of the London bombings on 7 July 2005 that killed 54 people. Fumes from the explosives made at a house in Leeds, UK, killed plants in the garden.
Önnerud's team told the ISADE symposium on explosives detection in The Hague, the Netherlands, on 10 October that they have successfully tested their sensors in the lab. The sensors are designed to pick up signs of explosives precursors, such as chemical reagents and reaction breakdown products. Each sensor comprises a number of 10-centimetre-long devices called ion-selective electrodes that are submerged in the wastewater flow of a sewer.
Only ions that come from the breakdown products of bomb-making chemicals can diffuse through the membranes in the electrodes, changing a resistor's voltage in a telltale way. Software looks for patterns in the concentration of target ions. Above ground, an infrared laser carries out a sweep of an area looking for the spectra of target gas molecules.
The Emphasis sensors have been developed and tested on faeces-rich wastewater in the lab and will be tested in real sewers next year.
The idea could have other uses. For example, epidemiologists have sampled wastewater to gauge urban drug habits. In 2011, Chang Chen and colleagues at the University of Adelaide in Australia used sewer data to demonstrate that ecstasy use in the city rose five-fold at weekends.
Instead of ad-hoc sampling, sensors could track drug use in real time – for example, monitoring usage patterns to inform public-health programmes. "We are thinking about illicit drugs detection and this could be the next aim we focus on," says the project's sensor specialist Frank Schnürer of the Fraunhofer Institute for Chemical Technology in Karlsruhe, Germany. The country's Ministry of Education and Research will be looking for research proposals for sewer-based drug detection soon, he says.
"Placing sensors in the sewer system may be a cheap and quick way to monitor illicit drugs, particularly by-products of their production which will be present in much higher concentrations than metabolites from users," says Chen.
Detecting explosives and drugs will not be easy, warns Rachel Cunningham of the innovation lab at Thames Water, which manages London's sewers. In addition to faeces and bacterial biofilms, the presence of detritus collectively known as "rag" – face wipes, sanitary products, condoms, and so on – means sensors will struggle to stay clean enough to operate.
And London's sewer architecture encourages solidification of cooking fat into pipe-blocking "fatbergs". One the size of a bus was removed in August. "It would be brilliant to have online sewer sensors that detect rising fat concentrations," says Cunningham's colleague Philip Thomas. "But no one has been able to develop one that works down there yet.
This article appeared in print under the headline "Flushed with success"
