Spying on our sewage

As well as picking up Covid-19, wastewater can tell how much we're smoking and how stressed out we are.

When looking for an infection like Covid-19 in the community, wastewater testing can pick it up on a scale of one part of the virus in one trillion parts.

"That's the equivalent of if you're looking at somewhere like the Auckland region, being able to see a single ping pong ball somewhere within that thousand kilometres," says Brent Gilpin, the science leader in the environmental science team at crown research entity ESR.

Before 2022, when New Zealand was treading the road less travelled of stamping out the virus, wastewater testing was a steel-capped boot. Outbreaks in places like Northland, Gisborne and Wellington were effectively tracked by picking up infected people's viral loads collected through the wastewater treatment systems.

"As it comes in, we have an autosampler set up that's collecting a little bit of waste every 10 or 15 minutes, so we get a 24-hour composite," Gilpin says of wastewater testing.

"We then take about a litre of that and send it to the laboratory, where we're able to concentrate that down, extract out the particular component we're interested in...chemicals, or DNA, or RNA or other microorganisms that might be present.

"It's a raw sewage sample, full of everything that sewage has. So mixtures of all the poo, wee, everything that comes from your sink, industrial inputs...it's not the most pleasant sample when it arrives."

Gilpin says New Zealand knows a lot more about the possibilities with wastewater testing now than it did three years ago.

He tells The Detail about the other areas where wastewater can shed light on how New Zealanders are living.

ESR has been monitoring the levels of drug usage around the country for years. The data is used by the government to evaluate the success of targeted policies, or to identify what areas may need them.

"The Southern region has cocaine usage...down in Queenstown. Places like Dunedin tend to have more ecstasy or MDMA, and Invercargill has higher levels of methamphetamine."

Cocaine usage is concentrated in Auckland and Queenstown because it is an expensive drug, meaning the people who live there tend to be more likely to afford to use it. 

"When we look at some of the drug usage over a week, then things like ecstacy or MDMA really peak in usage on a Friday and Saturday night...whereas methamphetamine [usage] we see it much more even over the week. Many people unfortunately become addicted and are really just having to consume that drug all through the week."

Abroad, wastewater surveillance has helped cities and countries defend against bioterrorism, detecting the spread of deadly diseases like polio and smallpox.

Gilpin says there is a risk of countries with preserved samples of eradicated diseases letting them loose - countries like Russia.

"The predecessors of ESR used to have smallpox vials in our laboratories, but they were - as part of a WHO decree - destroyed, so we don't actually have any of the live virus anymore stored in freezers. But I think some of the countries in the world may well still have them...countries that may be more inclined to use biological warfare."

Gilpin says ESR is exploring the use of wastewater testing to measure communities' tobacco and alcohol consumption, as well as people's stress levels expressed through stress hormones found in waste.

"I mean really, we can look at almost anything in wastewater. The question becomes what you want to do with the information, and what questions you want to ask about it," he says.

"One of the powerful things with wastewater-based epidemiology is trends over time. Is whatever you're looking at improving, or getting worse? And wastewater can be quite an objective way of making those measurements that's perhaps not influenced by political or government activities."

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