Microplastics are everywhere in Pennsylvania’s water – but the tide may be turning

Researchers have long known that . But how much plastic is trapped, and where, before it reaches the ocean is far less understood.

As professors of , , and at Penn State, we recently led studies mapping how across Pennsylvania. What we found was striking: Microplastics are nearly everywhere, their concentration in sediment has been doubling every 20 years, and some of the most common types are among the most toxic.

Plastic is everywhere, including inside us

Since the 1950s, about every 20 years. The world now produces annually - roughly the combined weight of every person on Earth.

Today, ends up in landfills, and less than one-tenth is recycled globally. The U.S. generates annually, and approximately 86% is sent to landfills. The domestic , making the U.S. a leading producer of plastic pollution. The rest enters the environment, where it breaks down slowly, potentially over , into microplastics. These particles range in size from 5 millimeters, which is about the size of a pencil eraser, to 1 nanometer - for reference, a single strand of human hair is about 80,000 nanometers wide.

are now found in the air, water, soil, food and living organisms, including humans. Microplastics enter the body through ingestion via what we drink, inhalation and skin contact. Studies have found microplastics accumulating in human , and .

To understand how plastics become a health threat, it helps to know how they’re classified in the first place. Plastics are sorted by the into seven categories in the U.S., identified by the numbered recycling triangle on the bottom of containers.

The mystery of missing plastic

- plastic that’s littered, dumped or otherwise not properly contained - is estimated to be transported by rivers to coastal environments.

Perhaps you’ve heard of the ? It’s the largest accumulation of ocean plastic in the world, located between Hawaii and California. It’s undeniably huge — but there is still than models predict there should be, given how much is produced and lost to the environment each year. In fact, millions of tons remain unaccounted for. Our team set out to investigate, in part, the mystery of the “.”

Our study focused on Pennsylvania’s Raystown Lake, Conemaugh River Lake and the John Heinz National Wildlife Refuge at Tinicum - .

We collected two types of sediment samples and asked three questions:

• Does land use - whether it’s urban, agricultural or forested - predict microplastic concentrations?
• Do reservoirs and estuaries trap plastic before it reaches the ocean?
• Which plastic types are most common - and most toxic?

Sediment cores - long cylinders of material drilled from riverbeds and lakebeds - gave us a chronological record of what was deposited over decades. We also collected surface sediment samples at intervals along each waterway, moving from densely populated areas near Philadelphia to sparsely populated regions, such as Raystown Lake and Conemaugh River Lake in central Pennsylvania.

Surprisingly, samples collected from a rural watershed in Raystown, a largely forested region in central Pennsylvania, exhibited similar microplastic levels to samples taken from John Heinz National Wildlife Refuge, a watershed located close to Philadelphia International Airport.

On average, we found about 1,125 microplastic particles per pound (2,500/kilogram) of sediment. But concentrations varied widely enough that land use alone can’t reliably predict how much plastic can be found in any given waterway.

Estuaries, which are partially enclosed coastal bodies where freshwater from rivers and streams mixes with saltwater from the ocean, - but not enough to account for the ocean’s missing plastic.

The most abundant types of plastic we found were polypropylene and polyurethane - both - along with . Single-use plastic, or disposable plastic, is any plastic item that is used once - such as bread bags, plastic bottles or straws - and then thrown in the trash.

Finally, we found that microplastic accumulation in Pennsylvania sediment has been doubling roughly every 20 years since 1950, mirroring the rise of global production. We determined this by drilling deep into sediment in reservoirs and estuaries, where layers of sediment build up over time like rings in a tree - older material on the bottom, newer on top. By of each layer, we could estimate when it was deposited and how much plastic it contained.

We dated the sediment layers using , the same basic principle behind . One method tracks , which decays at a known rate, allowing researchers to date each sediment layer. The other uses , a man-made isotope whose 1964 peak - tied to nuclear weapons testing - serves as a fixed time stamp in the sediment record. Together, these methods help build a timeline of when each layer of sediment and the plastic trapped in it were deposited.

A little bit of hope

Here’s where it gets slightly more encouraging. In the most recent sediment layers, which can be dated by depth and accumulation rate to roughly the 2000s, we found a small but measurable concentration. That could reflect better recycling rates and broader awareness of plastic waste. It’s modest, but it suggests the problem is at least partially responsive to human behavior.

Beyond recycling plastics, what can you do to decrease your exposure to microplastics and help decrease their spread? You can stay informed about which plastics carry the greatest health risks and check the recycling number on the bottom of containers before you buy. You can also swap out single-use plastic cups, straws and food containers for alternatives, such as glass, stainless steel or unbleached paper.