The Invisible Scrubbers at the Bottom of the Gowanus
In the “black mayonnaise,” a microscopic community has evolved to break down the toxic sludge.
he Gowanus Canal is known as a place where things go to die. In 2007, a malnourished baby minke whale wandered into the canal and swam in its oily sediment (earning the nickname “Sludgie” in the process) and died two days later. In 2013, an injured dolphin lost its way in the canal and didn’t survive the night. A number of small boats have met their ends, too. It’s a notoriously inhospitable place, due in part to the industry that once made the canal a vital commercial shipping hub. For a century, coal-processing plants, and industry that included tanneries, flour mills, and concrete works operated along the 1.8-mile waterway in Brooklyn and dumped their industrial waste into the stagnant water. The factories shut down in the 1960s, but the contamination continued: For the past decades, after heavy rains, stormwater has surged into a sewer system that wasn’t built to withstand the volume of sanitary waste; the raw sewage overflows and ends up in the Gowanus, too. Today, reflective fragments of coal tar cling to the water’s surface, striated in bands like a marble countertop. But most of the toxic stuff lies underneath, in the ten to 15 feet of sediment known as “black mayonnaise”: a mixture of carcinogenic PCBs, pesticides, and heavy metals like lead and mercury.
The toxic sludge is also replete with life, though invisible to the naked eye. Since 2014, Elizabeth Hénaff, a computational biologist at the NYU Tandon School of Engineering, has been studying the universe at the bottom of the Gowanus Canal. What she, along with a team of six scientists and landscape architects, discovered is a community of extremophiles: a class of microorganisms that can survive extreme conditions, whether that be related to temperature, acidity, or chemical concentration. And these extremophiles, Hénaff and her colleagues found, aren’t simply surviving in the hazardous liquid — rather, they’ve developed a miraculous ability to break down the canal’s noxious substances into its less toxic components.
These extremophiles didn’t emerge from nothing. “We’re not recreating the Big Bang in the Gowanus Canal and having life emerge from the primordial soup all over again,” said Hénaff. What we’re witnessing is adaptation. Whereas humans have a generation time of, say, 20 years, microbes have a generation time of something closer to 20 minutes. “So in the time that we’re talking now,” said Hénaff, snapping her fingers, “there will have been three generations of microbes.” The microorganisms are descendants of earlier ones that, after being exposed to the canal’s compounds for more than a hundred years, evolved the ability to degrade its most toxic components: toluene, used in industrial solvents; cresol, a petrochemical byproduct; and atrazine, an industrial herbicide that has been shown to turn male frogs into female ones.
In 2010, the Environmental Protection Agency had named the canal a federal Superfund site, a designation given to the most contaminated locations in the country. But it wasn’t until 2020, close to 263,000 generations of microbes and nearly a decade later, that small barges began dredging the black mayonnaise and shuttling the sediment into bigger barges. Next, the bottom of the canal will be capped with layers of clay, gravel and sand. The cleanup, estimated to be in excess of a billion dollars, coincides with one of the biggest rezoning projects in recent New York history, set to transform the rapidly gentrifying Gowanus neighborhood of Brooklyn into a hub of residential high-rises and retail shops. (Months after the cleanup started, one of the barges sprang a leak and started to sink, delivering some of the dredged waste right back into the Gowanus Bay.)
There’s no question that the canal’s contaminants pose a risk to those who reside along its shores; prolonged exposure to the canal’s water and sludge carries the risk of cancer and of ingesting viruses and parasites. When Hurricane Sandy made landfall in 2012, and the canal flooded, residents of the Gowanus neighborhood found their homes filling with the same polluted water they’d been long advised to avoid. Even the lionhearted have their limits when it comes to the Gowanus, like Gary Francis, a member of the Gowanus Dredgers Canoe Club, a group of canoe-enthusiasts who have advocated for the care of the canal since 1999. Long before the pandemic, the Dredgers would bump elbows in lieu of handshaking and keep sanitizer on deck. (There are times when even Francis will avoid paddling in the water, “like after a heavy rainstorm when all the Combined Sewer Overflows have been flowing,” he said. “It’s disgusting. You see everything.”)
But when the EPA finally cleans up these toxic compounds, the record of life that persisted at the bottom of the canal will also be erased — and with it, a form of cooperation among microorganisms that couldn’t be engineered in a lab. By studying the Gowanus sludge and the life that flourishes in it, Hénaff believes we could learn a thing or two about surviving in a polluted environment. We might even be able to harness their ability to clean up our messes.
