Mercury & Microplastic Pollution

Latest update October 11, 2018 Started on August 17, 2018

How does microplastic pollution in the ocean impact mercury chemistry? Join me as I explore San Francisco Bay and Lake Erie to discover the interplay between these two marine contaminants.

In The Field

San Francisco Bay is swimming with microplastics. A study published in 2016 found that on average, every square kilometer of the Bay contains 700,000 microplastic particles -that’s over 12 million tiny pieces of plastic floating in an area the size of a football field. Yikes. Treated wastewater discharged legally into the Bay is thought to be the leading contributor. Millions of fibers shed from synthetic clothing (i.e polyester, nylon) in commercial washing machines surpass filtration units in water treatment plants every day, gaining a free pass into San Francisco Bay. The authors of this study (5 Gyres Institute and the San Francisco Estuary Institute) have been busy with a follow-up investigation to quantify all sources and fates of microplastics in the waters surrounding one of America’s most populated cities.

Microplastic pollution may be front news page news today, but San Francisco Bay also has a long history with mercury contamination. During the California Gold Rush, mercury was used to extract gold from the Sierra Nevada mountains. Liquid mercury sticks to gold creating an amalgam that is easily separated by heat – mercury vaporizes into thin air leaving the gold behind. An estimated 8 million pounds of mercury were lost to the environment during this process, some making its way into San Francisco Bay. Mercury falls in the category of "legacy" pollutants – a group of contaminants that are toxic, bioaccumulate (increase in concentration) in the food web, and most importantly stick around for long periods of time.

The history of mercury contamination and documented microplastic pollution makes San Francisco Bay the perfect location for my study. I employed the help of the Bay Keeper, a local nonprofit that conducts regular boat patrols to monitor pollution in San Francisco Bay. I was joined by their Field Investigator Sienna and volunteer Skipper Fabio, a sailor and former Green Peace activist who took two days of vacation from his tech job to navigate us around the Bay. We were a cohesive team over two days of sampling, brought together by a shared eagerness to understand how microplastics are changing our environment. Tracking the incoming tides, Fabio guided us through the Central and South sections of the Bay where wastewater and river water are discharged. California receives little to no rain during the summer and the lack of precipitation resulted in low microplastic concentrations gathered in our manta net. Other researchers have found more microplastics in the Bay during the winter rainy season, but even under dry conditions we were able to collect enough samples to investigate our research questions.

image-1 image-1 image-1 image-1

Kaitlin, I'm loving your updates! Thanks for sharing your work with us

One of my main objectives for this study is to understand how mercury adsorbed to microplastics impacts wildlife. Sea birds, fish, and even organisms as small as zooplankton ingest microplastic particles, which they most likely mistake as food. Physical blockage of the stomach by indigestible plastic may causes death in some organisms, and those that survive are at risk of exposure to toxic chemicals concentrated on the plastic. Before leaving Cleveland, Ohio I stopped by the Westside Market to purchase local perch and walleye caught in Lake Erie. From each individual fish, I collected the stomach and a piece of fillet – I will dissect the stomach to search for microplastics and measure mercury concentration in the fish. My hypothesis is that fish with more microplastics in their gut will have a higher mercury concentrations in their fillet. Fish gut dissection beings this week!

image-1 image-1

I had originally planned to study microplastics in San Francisco Bay, but added Lake Erie as a study site after traveling home for the holidays. I was visiting my brother in Cleveland, Ohio on an unusually warm winter afternoon, and went for a run along the shores of Lake Erie. As I made my way down to the beach, I was struck by rainbow-colored sand. Plastic debris was covering the beach, it looked like the aftermath of a confetti strewn birthday party. I immediately made plans to ship my manta net to Ohio and include Lake Erie in this microplastic study.

As an oceanographer, I’ve spent a lot of time at sea and if there’s one thing I’ve learned about field work, it’s to be prepared for anything. After weeks of discussion and planning, the boat I hired canceled four days before our planned trip (mechanical issues). I scrambled to book the first company with a boat available and landed a rusty old walleye charter (that came with a salty old captain). This would do. I was joined by my friend and former lab mate Alison Agather from Wright State University. Alison and I have worked together everywhere from Ohio, to the North Pole, to the Mediterranean Sea. She was the perfect person to have by my side for this adventure.

At 6 AM, one hour before our schedule departure time, the rusty old walleye charter called to cancel. The waves had built up overnight during a thunderstorm and it wasn’t safe to go out. Determined to make this sampling trip happen, we convinced the captain to wait around and see if the winds calmed down. They eventually did, and at 9 AM, two hours behind schedule, we began our day.

For 8 hours the waves tossed around our tiny little boat as we trawled the manta net. Each trawl was filled with microplastics and trash flushed from the land into the Lake during the previous night’s storm. Cigarette butts, Black & Mild tips, bottle caps, Styrofoam, plastic wrappers. The heaviest loads of plastic debris came from the mouth of the Cuyahoga River near downtown Cleveland. We were surprised to find microbeads and nurdles at many of our sampling sites. Microbeads are used in cosmetic products like facewash and they’re small enough to bypass filtration systems at wastewater treatment plants. Nurdles are small plastic pellets that are melted and poured into molds to make plastic products; finding them in Lake Erie suggests an industry spill somewhere nearby.

No matter how far you live from the ocean, you are connected by a watershed. If you throw a piece of plastic on the streets of downtown Cleveland, Ohio, that plastic may drop down into the sewers and head straight for Lake Erie. If it missed the sewers, it will wash into a creek. That creek will drain into a river, eventually reaching Lake Erie. Water from Lake Erie crashes over Niagara Falls into Lake Ontario, eventually making it to the Atlantic Ocean through the Saint Lawrence Seaway.

Our captain chain-smoked Marlboro Reds the entire day while navigating through the waves. The combination of cigarette smoke, diesel fuel, and wave motion made our stomachs churn more than once, but Alison and I were able to keep it together. The day ended with bittersweet feelings, we had collected more microplastic samples than I imaged possible in one day. I was happy with my cooler of samples, but disappointed by how easy it was to collect.

Join Drink Local Drink Tap for a beach clean-up in Cleveland, Ohio to help prevent plastic waste from entering the Lake! (

image-1 image-1 image-1 image-1

One of the most important (and least glamorous) steps in expedition preparation...bottle washing! I use diluted hydrochloric acid and ultrapure water to wash away mercury and contaminants from all sample bottles and collection tubes to prepare for field sampling.

Microplastics are collected using a manta net. The manta has two large “wings” to help it stay afloat and a fine mesh net (< 1 mm openings). I borrowed a net from 5 Gyres, a non-profit organization that manages a trawl share program. The program lends manta nets to citizen scientists around the globe interested in collecting samples for a global data set of microplastics in the ocean. The two wings are easy to detach from the manta frame, I disassembled my net and shipped it to Cleveland, Ohio.

Before embarking on my first field day in Lake Erie I joined a group of researchers for a practice sampling trip in Monterey Bay. We embarked on a foggy morning passing under the Golden Gate Bridge and into the Pacific Ocean. I learned how to deploy and recover the manta net and how to collect microplastic samples while avoiding contamination. Microfibers from synthetic clothing are a big issue in San Francisco Bay, and all scientists had to wear natural clothing (i.e. cotton) to avoid contaminating the samples.

image-1 image-1 image-1 image-1
Expedition Background

Mercury is the most complex metal that cycles through our environment. Found naturally in Earth’s crust, solid mercury turns into an invisible gas when heated. Molten lava rising to Earth’s surface releases mercury that’s spewed into the air with volcanic ash and dust. The same process – heat turning solid mercury into a gas – occurs when we burn fossil fuels, especially coal, which is combusted around the globe to generate electricity. Much like increasing carbon dioxide in the atmosphere from human emissions, mercury is also on the rise. And this gaseous mercury can remain in the atmosphere for up to one year; as a result, mercury blankets our planet from pole to pole. No region is spared, not even the most remote corners of our planet.

Rain and dust transport mercury from the atmosphere to Earth’s surfaces where the chemistry of this toxic metal continues to change. Mercury is transformed to an organic compound called methylmercury by bacteria found in soil and water. Methylmercury is sticky and would much rather grab on to organic material (like phytoplankton and algae) than stay in the water. This results in bioaccumulation, or increasing concentrations of methylmercury moving up the food chain. Humans are exposed to mercury through consumption of fish, and top predator species (i.e. Tuna, Swordfish, King mackerel) deliver the highest dose. Methylmercury exposure has been linked to lower IQ in children and impaired cardiovascular health in adults. Many populations across the globe depend on fish and sea food as their main source of protein and have no other option than to risk mercury exposure to survive.

Plastic debris in the ocean breaks down into tiny fragments called microplastics that fish and sea birds mistake for food. Scientist have recently discovered the broad scope of plastic pollution in the ocean and are working towards solutions. Microplastics are important to the mercury cycle because they absorb mercury and provide a surface for bacterial biofilms. Follow my expedition to Lake Erie and San Francisco Bay to explore the interplay between mercury and microplastics in our environment.


Contribute to this expedition

Email Address
Number card
Postal Code

Review Your Contribution

You have chosen to contribute to expedition.

Confirm your details:

  • Name:

  • Email:

  • Last 4 digits:

Click below to proceed.

Thank You for Your Contribution!

Fundraising Details:


Tell us how raising these funds will impact your expedition
You're almost there, we just need to know three more things:
Is any part or component of your project funded by the National Geographic Society or a National Geographic Society Grant?
Is anyone on your expedition/project team affiliated, either currently or in the past, with the National Geographic Society?
Did you apply for a grant/funding from the National Geographic Society for this project?
You have a goal to raise by for:
How will raising these funds impact your expedition?
Is any part or component of your project funded by the National Geographic Society or a National Geographic Society Grant?
You’ve responded:
Is anyone on your expedition/project team affiliated, either currently or in the past, with the National Geographic Society?
You’ve responded:
Did you apply for a grant/funding from the National Geographic Society for this project?
You’ve responded:

Thank You

Fundraising is almost live!
Thank you for applying to collect contributions! We will review your request and follow up with next steps via email.
Feel free to email us if you have any questions.