The Effect of Microplastics on Oysters

Plastics continue to be produced at an unprecedented rate. While they may be cheap and convenient, plastics can also take hundreds of years to decompose, and are accumulating at an increasing speed in our environment.

Microplastics, composed of plastics that are 100 nm to 5 mm in size, are a classification of plastic that has either been deliberately manufactured at that size or has degraded from larger pieces of plastic. Plastics have been found almost everywhere in the environment, from the tops of remote mountains to the depths of oceans, with samples even collected from snow in the Arctic. In addition to polluting our air, water, and soil, recent studies have confirmed the presence of unwanted microplastics in common consumer products such as salt and bottled water.

At the University of Mississippi, we are conducting research to help us better characterize and understand the prevalence of microplastic pollution in oyster reefs and other coastal sites in the Mississippi Sound along the Gulf Coast. Through this research, it’s our aim to better understand the prevalence and threat of microplastics in order to better inform our ability to regulate and prevent this emerging containment from further entering our environment and our food chain.

Understanding Microplastics as an Emerging Environmental Contaminant

Microplastics have polluted our environment and are now pervasive in our oceans, lakes, rivers, air, and soil. Our oceans face an acute threat, with an estimated four to 12 million tons of plastic waste entering the oceans every year, posing a serious environmental threat to aquatic species.

Microplastics are damaging our ecosystem and negatively impacting our ocean life, threatening disruption and damage to the digestive tract if ingested. They also raise the risk of entanglement and a host of other negative consequences for aquatic species.

This interaction between microplastics and seafood can also have a negative impact on our food chain, both by contaminating the seafood we eat and by harming seafood populations. The majority of our seafood comes from estuaries and coastal areas, such as oyster reefs. It is in these estuaries and coastal areas that microplastics accumulate, due to the continual input and degradation of plastic litter from rivers and runoff.

Filter feeders like mollusks and oysters (Crassostrea virginica) are particularly vulnerable to microplastic pollution. However, few research papers have investigated the exposure of microplastics in oysters or by oyster reefs.

A Closer Look at Oyster Populations in the Mississippi Sound

Microplastics pose a significant threat to oyster populations, which have already decreased in recent years due to a combination of pollution (e.g., oil spills) and weather events, such as hurricanes and flooding.

To better understand this issue of microplastic prevalence in oyster habitats, we recently conducted a study examining the concentration of microplastic pollution in oyster reefs and other coastal sites in the Mississippi Sound, as well as the impact of freshwater inflows from flooding to these sites. We collected water samples from 10 sites, of which four were directly above oyster reefs.

Recent studies show that oysters nearer urban centers often contain higher concentrations of microplastics, which, given the prevalence of commercial fishing, oil drilling, and shipping ports in the area, implies that the Gulf Coast could be accumulating a considerable number of microplastics.

This was consistent with our findings, which estimated that oysters may be exposed to nearly 24,000 microplastics daily (range ~5,600 to ~36,000), understanding that concentration and filtering rates vary depending on other factors such as site-specific conditions and oyster species. To put this into perspective, humans are estimated to consume anywhere between 39,000 to 52,000 microplastic particles a year, meaning oysters are potentially exposed to half of our annual exposure every day. Overall, the study concluded that seawater along the Mississippi Gulf Coast had higher abundances of microplastics than what was observed in the Mississippi River and its tributaries to coastal areas.