Why we’re searching through your sewage for drugs

Wastewater testing provides an objective, standardised way of assessing levels of drug usage, and that has manifold benefits, writes Brent Gilpin of ESR.

There are suggestions from time to time that wastewater drug testing is an erosion of our civil liberties and freedoms, as if we’ve unwittingly dropped our trousers and given our “information” to the national database without giving our consent.

I’ve seen wastewater testing compared to camera surveillance, to work drug testing, and to consumer behaviour tracking.

However, it is clearly very different from those activities, all of which target individuals, and collect data, which can be traced back to named individuals.

Wastewater drug testing is community level evaluation, where no individual can be identified, and drug usage represents average usage of thousands of people contributing to a sewer.

The value of the current wastewater testing programme is that it provides an objective, standardised way of assessing levels of drug usage in New Zealand. The initial results from the first three months of the national wastewater testing programme covering about 80% of the population were released recently. Those results showed drug usage is a nationwide issue with patterns of drug usage differing around the country.

However, the real value of this type of testing is going to be in assessing the impact of interventions or changes in government policy.  What effect will potential changes to our cannabis laws, in terms of medicinal marijuana, decriminalisation, legalisation, or greater discretion by police in pursuing drug related prosecutions have on overall usage of various drugs? Will we see an increase or decrease in the use of different types of drugs, or no change at all?  For police and customs what impact do seizures, and drug busts have on usage? Is there a significant reduction in use, a change in usage (in some cases to potentially more harmful drugs) or does the drug stockpile and supply chain keep usage levels largely unchanged? In conjunction with other measures, it is hard to see a more objective and unbiased approach than the testing of our wastewater.

The drugs in sewage information are also useful for health agencies to assess the effectiveness of their drug abuse prevention activities and the resources required for drug treatment or rehabilitation. Clearly, the information so far demonstrates that illicit drugs are not just a big city problem. Ensuring regions receive sufficient specialist resourcing in hospitals and in support services should be a priority.

Of course, the drugs in wastewater is just one source of information, and data from that testing needs to be evaluated with that from other sources. While, it won’t reveal who

in a community is using drugs, whether it’s a small number of people using a lot of drugs, or a lot of people using a small amount of drugs, it should, however, be a quite robust indicator of changes in patterns of drug usage.

The issue of consent is an interesting point for discussion, and a discussion we as a society should have on all sorts of issues. What we flush down our toilets is stuff we want to dispose of, and it could be seen in the same way as rubbish.

The United States Supreme Court determined that when property or rubbish is thrown away or abandoned, anyone, including the police, could look through it and claim ownership once it has left the owner’s property. New Zealand law follows a similar approach, with case law based on an assessment of whether someone could reasonably be assumed to have abandoned something, in which case a finders keepers rule applies. Urine and faeces are not things too many of us are interested in finding, and I think it is fairly safe to assume that most of us are keen to abandon the stuff that enters our sewerage systems.  At that point, it is essentially in ownership of the council charged with transporting and treating it. Permission has been gained from each council involved for ESR to undertake testing of wastewater for drugs.

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Councils test the air for pollution from our fires and cars without our consent, and they test our rivers for bacteria and nitrates without our consent. The results are then published and reviewed so that trends in air and water quality can be assessed.

With no cost to individual privacy or time in gathering this information, this data can assist in provision of health services and policy decisions that ultimately impact (and hopefully benefit) all of us.

Wastewater has been described as a window on the soul of a city. Illicit drugs are just one of the things for which we can test wastewater. Antimicrobials, antimicrobial resistance genes, diseases, micro-plastics, organic and inorganic contaminants, are just some of the items we could evaluate which could inform on the actions, health and behaviours of our citizens.

I think part of our societal obligation is to support this use of science, which provides the opportunity to contribute not just to a fuller understanding of our society, but also to society’s needs.


The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.


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