Source: Su, L.; Cai, H.; Kolandhasamy, P.; Wu, C.; Rochman, C.; Shi, H. (2018). Using the Asian clam as an indicator of microplastic pollution in freshwater ecosystems. Environmental Pollution, 234, 347-355. doi: https://doi.org/10.1016/j.envpol.2017.11.075
What are microplastics?
Microplastics are pieces of plastic that are less than 5 mm in size; that is smaller than an ant! Microplastics are generally formed when larger pieces of plastic debris degrade into smaller ones (click here to learn more). Plastic pollution in the oceans has been an issue since the 1970s. However, in recent times researchers have shifted their focus from larger pieces of plastic to microplastics. These tiny pieces of plastic can accumulate in seafood that is eaten by humans. In addition, chemicals bound to the plastic can also be transferred to humans. This potential risk to humans has resulted in extensive research on microplastics in marine environments. In this paper, however, the researchers focused on microplastics in freshwater. Freshwater environments could be a source and transport pathway of plastics to the ocean, yet little research has been done on microplastics in freshwater.
How can clams help?
In marine environments bivalves (aquatic organisms enclosed in hinged shells, such as a mussels) are often used as bioindicators of microplastic pollution. A bioindicator is a living organism that reflects the condition of the environment it lives in. Bivalves are good bioindicators because they filter nutrients from the water to eat. While removing nutrients they can also remove pollutants and accumulate them in their tissue. The researchers in this study wanted to determine if another bivalve (clams) could be used as bioindicators of microplastic pollution in freshwater environments. As mentioned before, far less is known about microplastic pollution in freshwater than marine systems.
Specifically, the researchers were interested in the Asian clam (Corbicula fluminea) (Figure 1). There are several reasons the researchers focused on the Asian clam. First, the clam has been used as a bioindicator for other pollutants in freshwater environments. Second, they are found all over the world in many different types of freshwater systems. Lastly, in a previous study conducted by the same set of researchers, they found microplastics in an Asian clam.
What: The researchers measured the amount of microplastics in clams, water, and sediment.
When: The study was conducted from August to October.
Where: The samples were collected from the Middle-Lower Yangtze River Basin in China. The researchers examined three types of freshwater systems: lakes, rivers, and estuarine areas.
Why: To determine if the Asian clam can be used as a bioindicator for microplastic pollution in freshwater environments.
How: The researchers used a filter to collect microplastics from the clams, water, and sediment. They also used a special microscope to take photos of the microplastics found.
The researchers found microplastics in the clams, water, and sediment from all of the sites sampled, but the amount differed between sites. The researchers hypothesize that the difference in abundance of microplastics is related to the amount of industrialization and hydrological conditions. For example, some of the highest microplastic pollution was in rivers located in urban areas that have small water volumes.
The researchers also determined that the amount of microplastics in clams was similar to that in both the water and sediment. Therefore, the researchers concluded that the Asian clam can be used as a bioindicator of microplastic pollution in freshwater ecosystems.
There are three advantages of using the Asian clam as a bioindicator. First, it allows researchers to evaluate which microplastics pose ecological risks. Second, the Asian clam is found all over the world and is easy to sample through collection. Finally, because the Asian clam is consumed by humans, it could be an important step to understanding the risk of microplastics to humans.
Long story short
To summarize, freshwater systems are polluted with microplastics that could potentially harm both humans and wildlife. However, this study showed that Asian clams can be used as bioindicators (or in other words to monitor) for microplastics in freshwater environments. This will help us determine hotspots of microplastic pollution and better understand how microplastics can move up the food chain.