For more than 150 years, industrial pollution, chemical waste, and sewage have flowed into Brooklyn’s Gowanus Canal. The New York City waterway is often described as one of the most contaminated in the United States. It was dredged and developed from a tidal wetland and a freshwater creek into its current form in the mid-1800’s, in order to serve as an urban cargo transportation route. Though the paper mills, petroleum plants, tanneries, and manufacturers that once lined its banks are now gone, their legacy of toxic dumping and discharging remains–not to mention the combined sewer overflow that still spills directly into the canal.
“It’s accumulated anywhere from ten to twenty feet of contaminated sediment at the bottom of the canal,” says Elizabeth Hénaff, a computational biologist at New York University.
Yet amid all that toxic muck, life finds a way. Microbes in the Gowanus sediment have evolved methods of coping with and even subsisting off of the contamination, according to new research co-authored by Hénaff. Hundreds of hardy microbe species, equipped with dozens of metabolic pathways for breaking down pollution, live at the bottom of the canal, per the study published April 15 in the Journal of Applied Microbiology. These bacteria, archaea, and viruses are slowly sequestering heavy metals and eating their way through some of the worst compounds lingering in the mud.
The silver lining of the slo-mo environmental disaster is that engineers and biologists might have the chance to harness these superfund superbugs to help detoxify the Gowanus and polluted sites elsewhere. This process known as bioremediation has been applied to challenges like wastewater treatment and cleaning up oil spills, including the massive 1989 Exxon Valdez incident in Alaska. In this way, the “sludge” becomes a “reservoir of potential solutions,” says Sergios-Orestis Kolokotronis, a study co-author and an evolutionary biologist and epidemiologist at SUNY Downstate Health Sciences University.
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To discover the canal’s hidden potential, Hénaff, Kolokotronis, and their colleagues conducted the first detailed microbial and genetic survey of the Gowanus. They paddled out onto the infamous waterway and collected sediment samples from the top layer of sunken gunk using a PVC pipe. They also obtained a deeper sediment core from an environmental contractor working with the Environmental Protection Agency (EPA).
Simply getting the samples was no easy feat. “It’s not the same thing as going to the park and picking up soil,” says Kolokotronis. “This is dangerous for everyone involved in the canoes,” he adds. In many cases, the researchers had to trespass to access sites. Then, there’s the water and muck itself, which necessitated full personal protective equipment to minimize contact.
Back in the lab, the scientists analyzed the DNA in these samples to identify the species present and dig into their genetic makeup. They compared the Gowanus data with previously documented organisms and their functions from other databases.The team found 455 different microbe species (including salt and temperature extremophiles), 64 metabolic pathways known to degrade organic contaminants like phenols and toluene, and 1,171 genes related to heavy metal uptake. They also classified thousands of previously un-cataloged gene clusters and metabolites with potential for breaking down pollutants.
It’s the first step in what could be a valuable long-term project, says Max Häggblom, an environmental microbiologist at Rutgers University in New Jersey who was not involved in the new research. The Gowanus is “such a chemical soup,” Häggblom says. “That makes it really interesting for microbiologists because it’s basically a hot spot for selection and evolution of microorganisms with the ability to degrade these different chemicals.”
Häggblom agrees the canal could be a useful source of toxin-fighting organisms. But to know for sure, we’d need lab experiments tracking the presence and concentration of pollutants over time in a mini-Gowanus microcosm.
If the microbes really can break down pollution, they could be “mined” for all sorts of bioremediation projects. Organisms grown and stored in bioreactors might help filter through contaminated water and mud. Alternatively, shifting the environmental conditions of a waterway slightly (for instance, adding the right mix of nutrients) to promote beneficial bacteria could speed up environmental recovery with minimal cost and disruption. Sediment dredged up through the ongoing EPA superfund remediation project might be rendered less dangerous before landfilling by being purposefully mixed and steeped with these helpful bugs.
The findings also act as a ground truth of the types of pollutants in the canal, say Hénaff and Kolokotronis. “These microbially kept records can be more accurate than human kept records,” Kolokotronis explains. The microbe adaptations prove the presence of toxins that have gone otherwise undocumented in the environmental monitoring and regulation of the waterway. “There’s something poetic about the memory of these organisms,” he adds. In addition to the science, the researchers also synthesized their findings into a public art exhibit about the Gowanus Canal’s history and microenvironment, called CHANNEL.
According to Häggblom, it’s marvelous, though not surprising, that these types of microbes routinely emerge under such hostile conditions. Many microorganisms can swap genes with one another, allowing the spread of useful traits without each species having to individually go through the gauntlet of mutation and natural selection. Under the pressure of trying to survive in a toxic environment, and without the standard resources for energy production like oxygen, bacteria and viruses frequently share the alternate solutions they come up with: including methods of using chemicals like PCBs and hydrocarbons to breathe, he explains. “This is nature taking its course.”
Yet despite the wide array of pollution-munching microbes present in the Gowanus, they aren’t capable of fully cleaning up the canal on their own. For one, though many of the microorganisms sequester heavy metals like cobalt and arsenic, the microorganisms can’t actually eliminate those toxic elements. The only way to remove the metals is to scoop them out of the waterway once they’re contained. The microbes could play a role in recycling these metals for new uses. “It’s an exciting possibility,” says Hénaff. Many of the canal pollutants are resources in a different context. “A lot of the heavy metals among the toxic contaminants are being mined elsewhere to serve as a resource for technology and industry,” she notes. Though that, again, requires human-microorganism collaboration.
Other, non-metal, organic pollutants present in the Gowanus can be broken down into non-toxic forms by microbes alone. But not at the ideal speed and scale. Left to their own devices, the microbes would take centuries or even millennia to work their way through the contamination, says Häggblom.
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As the Gowanus continues to stew in the open, it poses a perpetual public health risk– exposing nearby residents to unhealthy air and soil. One of the less pleasant study findings was that the canal also harbors a wide variety of genes for antimicrobial resistance. The danger is why the EPA has been working to dredge and cap the Gowanus’ toxic sediments. Ultimately, that’s probably the correct call, says Hénaff.
But until the sludge is permanently buried and the microbes dead beneath a concrete tombstone, why not treat the canal as more than a mistake? Why not learn everything we can from the polluted world we accidentally built?
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