Advanced method to detect harbour sewage

Macquarie University researchers have investigated the level of sewage pollution in 18 global harbours, with concerning results. Their work was part of an international study using a special DNA technique that the researchers say is more targeted than traditional methods.

The team’s findings have been published in Nature Water.

In contrast to other approaches, which may use E. coli or enterococci to detect sewage pollution, the researchers employed molecular techniques that use human-gut microbial flora DNA to detect sewage contamination.

This began by finding a ‘global signature’ that could be used to distinguish sewage from other harbour contaminants.

“We sequenced untreated sewage samples to find global-wide human gut markers; this approach makes indicators specific to humans, unlike E. coli which can also come from wildlife and domestic animals (such as bird and animal droppings),” said Molecular Ecologist Associate Professor Anthony Chariton from Macquarie University.

Led by Chariton, along with Professor Sandra McLellan from the University of Wisconsin, and Professor Peter Steinberg from the University of NSW, the research was funded by the Sydney Institute for Marine Sciences World Harbour program and involved partners from Australia, China, USA, Italy, France, Spain, Singapore and Brazil.

Sydney, Melbourne and Darwin harbours were part of the Australian group of waterways tested, while Hong Kong, San Francisco, Honolulu and Singapore were among the international locations included in the study.

“The study demonstrated that there is indeed a global molecular signature for raw sewage, making it possible to develop global indicators,” Chariton said.

The team’s advanced approach revealed that about half of all water samples from around the world contained measurable concentrations of human faecal bacteria markers, showing evidence of sewage contamination in harbours.

“These samples far exceeded previous estimates, and our own data based on conventional testing methods showed just 18% of samples were polluted,” Chariton said.

The new approach can cast light on whether harbour pollution comes from structural problems such as overflow or inadequate sewage treatment — this would allow harbour cities to more accurately assess the effectiveness of water treatment infrastructure.

“An estimated 40% of the world’s population lives within 100 kilometres of the coast, and rapid urban expansion puts massive pressure on water resources and their management, with sewage contamination posing a significant threat to both human health and the services water bodies provide,” Chariton said.

Many of the contaminated sites were found to have bacterial communities that originated in sewage infrastructure — that is, they showed bacteria that normally live within pipes.

Chariton said the findings provide urban planners, policymakers and water resource managers with a new range of tools to better manage and protect aquatic environments.

As cities continue to grow and climate change increases the frequency of extreme weather events that can overwhelm sanitation infrastructure, addressing sewage contamination of coastal waters will only become more critical, he added.

Image caption: Watsons Bay in Sydney Harbour, one of the locations tested by researchers. Image credit: iStock.com/RugliG