Thursday, June 19, 2014

What your sewage tells about you

Here’s my latest piece for BBC Future, pre-editing. I was going to illustrate it with that scene from Trainspotting, but I feared no one would have the stomach to read on.


“They found him in the toilet covered in white powder and frantically trying dispose of cocaine by emptying it down the toilet.” But it’s not just during a drugs bust, as in this report of an arrest in 2012, that illicit substances go down the pan. Many drugs break down rather slowly in the body, and so they are a pervasive contaminant in human wastewater systems. The quantities are big enough to raise concerns about effects on ecosystems – but they can also offer a way to monitor the average levels of drug use in communities.

“Sewage epidemiologist” does not, it has to be said, sound like the kind of post that will bring applications flooding in. But it is a rapidly growing field. And one of the primary goals is to figure out how levels of drug use obtained by more conventional means, such as questionnaires and crime statistics, tally with direct evidence from what gets into the water. Over the past six years or so, sewage epidemiology has been shown to agree rather well with these other approaches to quantifying drug abuse: the amounts of substances such as cocaine and amphetamines in wastewater in Europe and the USA more or less reflect estimates of their use deduced by other means.

A new study, however, shows that the figures don’t always match, and that some previous studies of illicit drugs in sewage might have under-estimated their usage. To appreciate why, there’s no option but to dive in, in the manner of the notorious toilet scene from the movie Trainspotting, and embrace the grimy truth: you might not discover as much by looking at drugs carried in urine and dissolved in water as you will by studying the faecal residues in suspended particles and sewage sludge, since some drugs tend to stick more readily to the solids.

While a few studies have looked at illicit drugs in sewage solids in Europe, Bikram Subedi and Kurunthachalam Kannan of the Wadsworth Center of New York State’s Department of Health in Albany have conducted what seems to be the first such study in the USA. They took samples of wastewater and sludge from two sewage treatment plants handling the wastes of many thousands of people in the Albany area, and carried out chemical analysis to search for drug-related compounds. They looked not only for the drugs themselves – such as cocaine, amphetamine, morphine (the active component of heroin) and the hallucinogen methylenedioxyamphetamine (a designer drug known as “Sally” or “Sass”) – but also for some of their common ‘metabolites’, the related compounds into which they can be transformed in the body. The two researchers also measured amounts of common compounds such as nicotine and caffeine, which act as chemical markers of human excretion and so can serve to indicate the total number of, shall we say, contributors to the sewage.

To measure how much of these substances the samples contain, Subedi and Kannan used the technique of electrospray mass spectrometry. This involves converting the molecules into electrically charged ions by sticking hydrogen ions onto them, or knocking such ions off, and then accelerating them through an electromagnetic field to strike a detector. The field deflects the ions from a straight-line course, but the more massive they are the less they are deflected. So the molecules are separated out into a “spectrum” of different masses. For fairly large molecules like cocaine, with a molecular mass of 303, there’s pretty much only one common way atoms such as carbon, oxygen, nitrogen and hydrogen can be assembled to give this mass (formula C17H21NO4). So you can be confident that a spike in the spectrum at mass 303 is due to cocaine.

From these measurements, the researchers estimated a per capita consumption of cocaine in the Albany area four times higher than that found in an earlier study of wastewater in the US, and a level of amphetamine abuse about six times that in the same previous study, as well as 3-27 times that reported for Spain, Italy and the UK. It’s still early days, but this suggests that sewage epidemiology would benefit from getting to grips with the solids.

Subedi and Kannan could also figure out how good the sewage treatment was at removing these ingredients from the water. That varied widely for different substances: about 99 percent of cocaine was removed, but only about 4 percent of the pharmacologically active cocaine metabolite norcocaine. A few drugs, such as methadone, showed apparently “negative removal” – the wastewater treatment was actually converting some related compounds into the drug. The researchers admit that no one really knows yet what effects these illicit substances will have when they reach natural ecosystems – but there’s increasing concern about their possible consequences. It looks as though we might need to start thinking about the possibility of “passive drug abuse” – if not in humans, then at least in the wild.

Reference: B. Subedi & K. Kannan, Environmental Science & Technology online publication (2014).

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