Delaware River may be dumping more plastic into ocean than any other U.S. waterway

New report cites large number of landfills in region as part of the problem, along with population density, river size
Credit: Public Domain Photos via Creative Commons licensed under CC BY 2.0
Plastic pollution along riverbank

Each year just over 283,000 pounds of plastic waste are carried by the Delaware River and ultimately dumped in the ocean.

That puts the Delaware at the low end of the 1,656 rivers the authors of a new paper published in the journal Science Advances say contribute 80% of the plastic waste that ends up in the sea.

The study, which underwent two years of peer review, was funded by The Ocean Cleanup, a Dutch nonprofit that has gained international attention — though some might say notoriety — for its attempts, so far unsuccessful, to build a collection device to clean up the Great Pacific Garbage Patch, a swath of Pacific Ocean where currents have created a large concentration of plastic trash. The paper refines to a great degree a pair of 2017 studies that claimed between 10 and 20 rivers account for the vast majority of the riverine-derived plastic waste that ends up in the oceans.

Those early studies largely focused on river size and outflow and adjacent population density. The Ocean Cleanup considers those factors, but also the proximity of rivers to ocean coasts; rainfall and wind conditions; land slope; and contiguity of landfills, paved surfaces and other elements of the built environment that can fast-track trash into waterways.

Plenty of blame to go around

The striking shift in blame for such pollution coming from just a handful of rivers to over 1,000 underscores the fact that much more research needs to be done into the precise sources of plastic trash in the oceans, both micro and macro. Microplastics are typically the size of an eraser tip and smaller and are often fragments of larger items; macroplastics are generally intact, like plastic bottles, caps and food wrappers.

Studies like this one are important but shouldn’t be taken as conclusive, said Bob Chant, a physical oceanographer and Rutgers professor who studies the transport of plastic waste from New Jersey’s urban estuaries to the ocean.

“This is a new and developing field,” Chant said. “It’s challenging because you have all these sources of data collected using different sorts of techniques, from actually collecting the trash to simply observing it from bridges — it’s a hard problem that’s really variable.”

Chant points to his own research into New Jersey’s rivers. “We can go out there one day and collect 100 microplastics per cubic meter, then go out a month later and find one,” he said.

Needs further study

Even the study’s authors concede that “riverine plastic transport remains understudied, especially in areas that are expected to contribute most to global plastic emissions into the ocean,” which they estimate ranges from 0.8 million to 2.7 million metric tons per year — the equivalent to about 146,000 dump trucks.

Nevertheless, Chant says that the study’s estimate of 283,000 pounds of plastic waste entering the Delaware River annually seems reasonable. “It’s densely populated,” he said. “And pollution scales with population, so it’s not surprising that the Delaware is in the top 1,000.

“What we really learned,” said Lourens Meijer, the study’s lead author, “is that areas where the population lives near rivers, lives near coastlines, these areas have the highest probability of emitting plastic into the ocean.”

In other words, with people comes more trash.

Of the U.S.’s 550 operational landfills, 75 are located in New York, Pennsylvania, New Jersey and Delaware, according to the Environmental Protection Agency. Pennsylvania’s 37 is the third-highest number in the country. A 2016 study by the electricity brokerage SaveOnEnergy found that Pennsylvania holds 35.4 tons of waste per person in its landfills, a volume eclipsed only by Nevada. New Jersey and Delaware aren’t far behind.

A glut of landfills

These landfills are not intentionally dumping plastic waste into the river and its tributaries, of course, but the fact that they account for nearly 15% of the U.S.’s operational landfills serves to highlight just how many people live within the Delaware River Basin — 8.3 million, according to the Delaware River Basin Commission.

But not all of our waste makes it into — or remains contained in — landfills. People litter or dump illegally. Wind and rain transport trash from dumpsites. Plastics that should be recycled are not. All of this “mismanaged plastic” in the Delaware River Basin, The Ocean Cleanup study noted, amounts to some 50 million pounds annually.

Much of this mismanaged plastic never makes it as far as the ocean. Nevertheless, plastic is pervasive throughout the landscape, from creek- and riverbanks, to vacant lots, storm drains and beyond. It has been estimated that 60% of all the plastics ever made have been dumped into landfills or directly into the environment — and virtually all of it still exists in some form.

And it is only accumulating. China once took in nearly half of the world’s recyclable waste, but in 2018 the country banned plastics imports. With its primary pipeline cut off, the United States experienced an immediate backup of trash with nowhere to go. Many landfills have now stopped accepting some recyclables.

“It’s a big concern,” said Sen. Linda Greenstein (D-Mercer and Middlesex), who was one of the lead sponsors of the single-use bag ban signed into law by Gov. Phil Murphy in September. “That change means we have to think about how we’re going to handle all those recyclables, and how we can come up with new methods here.”

Last June, along with Sen. Bob Smith (D-Middlesex and Somerset), Greenstein also introduced a bill that would require trash bags and plastic, glass and paper carryout containers to be made in part with recycled content, and ban the sale of polystyrene packaging. “The bill is one example that would help the economy for recycled plastic,” Greenstein said. “Coupled with the single-use bill, that would make us generate less plastic.”

The Ocean Cleanup spent years focused on plastic pollution in the Pacific Garbage Patch, drawing intense criticism from oceanographers and other experts who said the tens of millions of dollars the nonprofit was spending to build an improbable midocean collection system would have been far better spent on addressing rivers, where plastic trash is concentrated and can be captured far more easily. With the failure of the scheme, the group has been forced to pivot, finally redirecting their enormous sources back toward the land.

“Going to the rivers is a much more intelligent way of tackling the problem,” said Chant. “Some plastic washes off of beaches or is dropped off of boats, but the vast majority of it is going to go through rivers and into the ocean.”

A dataset as granular as the one developed for this study — the authors analyzed observations of nearly 32,000 river mouths — also provides crucial insight that national, state and local leaders can use to pinpoint areas in their districts where plastic waste is entering the water. Along the Delaware River and Bay, for example, the study includes more than a dozen tributaries and the volume of plastic waste they’re contributing to ocean plastic waste.

“The public may question some of the steps we’re taking,” Greenstein said, referring to the single-use ban and recycled contents bill. “We want to make sure that we can tell them what studies like this have shown. This is all very important information, so that as we make these policy changes, they are based on the science.”

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