Findings from a new study published in the journal Environmental Pollution show that clams can act as a litmus test for ecological risks of plastic pollution.
Researchers in China discovered microplastics in Asian clams in the Yangtze River to be representative of microplastic pollution in the river’s ecosystems.
“The levels of microplastics in the Asian clam can serve to track the amount of microplastics that may be available to marine animals of a similar size,” say the authors. “From an ecological perspective, Asian clams can provide a snapshot of what can be ingested across a large area.”
Microplastics are tiny plastic particles that are smaller than 5mm—or about the width of a pencil.
These small particles were detected at high levels in 96% of Asian clams sampled. At these levels, researchers say, habitat contamination and transfer to other organisms is likely.
Clams were chosen as “indicators” of microplastic pollution because they are filter feeders—essentially acting as a strainer trapping food and other small particles in water.
Along with clams, sediment and water were collected for microplastic analysis at 21 sites along the Yangtze river. Within those study areas, three different ecosystems were selected: lakes, rivers, and estuaries—transition zones where saltwater meets freshwater.
To isolate microplastics, the researchers used a series of elaborate filters, nets, and vacuums.
Levels of microplastics varied greatly across the three ecosystems. Rivers contained higher levels, which could be attributed to lower water volume, or even proximity to industrial plants.
“Some of the rivers are located in urban areas and receive more wastewater than lakes,” the authors say. “Sediments in river drainage areas are also likely hotspots for microplastics.”
Microplastics are ubiquitous in marine environments. These particles have pervaded every marine ecosystem in the world. Plastic pollution found in marine animals has ran the gamut from sea birds, sea snakes, and sea turtles to penguins, seals, and sea lions.
The extent of microplastic pollution in freshwater systems—like lakes and rivers—is less clear. However, recent studies are beginning to paint a bigger picture.
A few months ago, scientists in Germany discovered that rivers are responsible for a considerable amount of marine plastic pollution—with rivers in Asia being a heavy contributor.
Although this pollution can seem distant to humans, we are not isolated from it. Shellfish, such as the Asian clam, are a source of nutrition for billions of people, and are widely consumed throughout China. People typically eat clams without removing the digestive tract. As a result, the contents of a clam’s stomach—and plastics within it—become the contents of the consumer’s stomach. Ingestion of these microplastics is a possible health risk and has been shown to cause inflammatory reactions.
“Few studies have determined the level of microplastics exposure from freshwater shellfish consumption,” say the researchers of the current study. “So, it will be valuable to set the baseline for microplastic consumption by humans. Potential human health risks should not be ignored.”