Anneka Johnson F23’s Div III Focuses on Microplastics in Fish in Different Ecosystems

As part of their experience, students each complete an independent research project working with top scientists in the field. Anneka’s work became the basis of her Div III on pollutants in fish. We caught up with her to talk about her research and what comes next.

Tell us about your project.

My project was titled “Contaminants in Organisms Across Trophic Levels: Microplastics and Metals,” which, in simpler terms, means I was looking at microplastics and other pollutants, such as copper and zinc, in fish and their prey to see if microplastics biomagnify up the food web (increase in concentration at successively higher levels on the food chain), as heavy metals do not.
 
I sampled from a highly populated area (expecting more pollutants) called Childs River and a less populated area (expecting fewer pollutants) called Sage Lot Pond. I collected shrimps, mussels, crabs, snails, small fish, and large predator fish, then performed isotope analysis as well as nitric acid digestion and heavy metal measurements on them.
 
Isotope analysis consists of drying samples, grinding them into a fine powder, packing them into tin capsules, and running them through a machine called the isotope ratio mass spectrometer in order to gauge their carbon and nitrogen ratios, which explain an organism’s trophic level (where it sits on the food chain).
 
To perform nitric acid digestion, I dry my samples, apply a specific quantity of nitric acid, and heat them. Once the samples are cooled, I filter each one to separate any plastics from the remaining liquid. I then observe the filters under a microscope and count the plastics present within each sample.
 
When looking for heavy metals, I run the remaining solution from the filtering process through an atomic absorption spectroscopy instrument to look for copper and zinc, in addition to running standards and blanks that allow my measurements to be accurate.
 
Averaging data for each site, a clear difference emerged, suggesting that although contamination varies among species, the overall contamination levels in Childs River are substantially higher than in Sage Lot Pond, likely influenced by the levels of population density and land use surrounding the two sites.
 
When examining the relationship between contaminants and trophic levels in both bodies of water, an interesting trend emerged: Organisms with lower trophic levels (such as shrimp) often exhibited higher concentrations of microplastics and metals than species at the top of the food web, like striped bass, which had near-zero microplastics. No evidence of bioaccumulation of plastics up the food web.

Conclusion?

Microplastics, zinc, and copper were not observed to biomagnify as trophic level increased in our two study sites, suggesting that these contaminants don’t accumulate as they move up the food web. Microplastics were, however, detected in the majority of organisms sampled, demonstrating their persistent presence in the environment.

What’s next for you after graduation?

I’m planning to look for a career where I can be outside. I’ve always been deterred from the thought of being inside an office or building for the next 40 years of my life. Possibly, I’ll try to get a job with Mass Wildlife or even move back to Woods Hole to conduct more research, since there’s still a lot unknown on microplastics and how they act in the environment. If getting a job without a master’s seems to be difficult, I’ll go to grad school.

Any words for a student considering Hampshire?

Hampshire is a great school. It lets students explore specific fields and subjects that interest them without restriction. Students can learn what they want to instead of having to take classes they don’t find important.