An international study published in Nature Water has uncovered wide-spread sewage pollution in urban harbours across five continents.
Evidence: Researchers tested a variety of locations around Sydney Harbour including Watsons Bay, pictured, and found the presence of human sewage was a common problem.
The researchers used molecular techniques on harbour water samples which use human-gut microbial flora DNA to detect sewage contamination on a global scale.
Molecular Ecologist Associate Professor Anthony Chariton from Macquarie University said the researchers 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),” he says.
Led by Professor Sandra McLellan from the University of Wisconsin, Associate Professor Chariton from Macquarie University and Professor Peter Steinberg from the University of NSW and funded by the Sydney Institute for Marine Sciences World Harbour program, the study involved partners from Australia, China, USA, Italy, France, Spain, Singapore and Brazil.
Highlighting the source
“Pathogens are generally very difficult to detect as they are found in very low concentrations, so to monitor water quality, surrogates such as E. coli in freshwater and enterococci in marine environments are used,” says Associate Professor Chariton.
Molecular innovation: Scientists have used bacterial DNA from human-gut microflora to track sewage pollution in 18 global harbours, including Melbourne's Port Phillip Bay, pictured, revealing widespread contamination that current testing methods fail to detect.
However, most monitoring to test if water is safe for swimming, such as the Beach Watch and River Watch programs in NSW, uses culturing techniques which require the bacteria to be alive, and hence only measure recent events.
They are also not animal-specific; for example, whether an E. coli outbreak occurs because of a large bird population, or because of a sewage system failure, will have very different health risks and management solutions.
To address these limitations, in this global study, encompassing 18 harbour cities across five continents, the research team introduced a new way to measure water samples collected from each harbour, using molecular tools to measure bacteria associated with human gut flora as indicators of sewage.
Sydney, Melbourne, Darwin Harbours were part of the Australian group of waterways tested, with Hong Kong, San Francisco, Honolulu and Singapore 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,” says Associate Professor Chariton.
New test method reveals sewage pollution
The advanced techniques showed around half of all water samples from around the world contained measurable concentrations of human faecal bacteria markers, showing evidence of sewage contamination in harbours.
Global testing: Water samples from Hong Kong's Victoria Harbour, pictured, were tested for bacteria linked to human gut flora as part of a world-wide research project examining water quality.
“These samples far exceeded previous estimates, and our own data based on conventional testing methods showed just 18 per cent of samples were polluted,” says Associate Professor Chariton.
Using this new approach to water quality testing can highlight when harbour pollution comes from inadequate sewage treatment, overflow and other structural problems - and will allow harbour cities better monitor for their water treatment infrastructure.
The findings have far-reaching implications for the health of urban waterways.
“An estimated 40 per cent 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,” says Associate Professor Chariton.
The research also revealed that many of the contaminated sites had bacterial communities that originated in sewage infrastructure – that is, they showed bacteria which normally live within pipes.
“This approach can highlight more long-term, structural issues," Associate Professor Chariton says.
He says the findings provide urban planners, policy makers 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 says.
While the findings are concerning, they also highlight opportunities for improvement.
“By adopting more sensitive and specific testing methods, cities can gain a clearer picture of sewage contamination in their waters and take more targeted action to address the problem,” says Associate Professor Chariton.
Associate Professor Anthony Chariton, pictured, is a molecular ecologist in the School of Natural Sciences, Macquarie University.
