Alexei Volkov
Animals are known to eat plastic, which can lead to their deaths. Seabirds, albatross chicks, fish, turtles, seals, whales, camels, and other marine mammals are among the many species that have been found with plastic in their stomachs. The question of why animals eat plastic has been explored by scientists, who have found that plastic may smell like food to some animals, and can also resemble their natural food in appearance.
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What You'll Learn
Plastic smells like food to animals
Marine animals are known to eat plastic because it looks like food. Sea turtles, for example, often mistake flimsy, clear plastic bags for jellyfish. Other marine animals, including fish, eat bits of rice-sized microplastics broken down by sunlight and wave action because they resemble the small particles they normally eat.
However, the sense of smell also plays a role in marine animals' consumption of plastic. A study led by Matthew Sovaca, a doctoral student at the University of California, Davis, found that the stinky sulfur odor known as dimethyl sulfide (DMS) emitted by algae as it breaks down in the ocean attracts seabirds in search of krill, their primary food source. Floating plastic debris provides the perfect platform for algae to thrive, and as the algae break down, emitting the DMS odor, seabirds follow their noses into an "olfactory trap".
This does not disprove that plastic might look enticing, but it is far more likely that a seabird will eat it if it looks and smells like food. Seabirds are especially at risk, with a study by Australian scientists concluding that virtually all seabirds have consumed plastic.
The ingestion of plastic by wildlife was first observed in 1966, when researchers found plastic container lids and toys in dead Laysan albatross chicks. More than 200 animal species have been documented consuming plastic, including turtles, whales, seals, birds, and fish.
Plastic accumulating in our oceans and on our beaches has become a global crisis, with a direct and deadly effect on wildlife. Thousands of seabirds and sea turtles, seals, and other marine mammals are killed each year after ingesting plastic or getting entangled in it.
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Plastic looks like food to animals
Marine animals are known to eat plastic because it looks like food. Sea turtles, for instance, often mistake flimsy, clear plastic bags for jellyfish. Other marine animals, including fish, eat rice-sized microplastics because they resemble the small particles they normally eat.
Seabirds are especially at risk. A study by Australian scientists concluded that virtually all seabirds have consumed plastic. Seabirds are attracted to DMS, a stinky sulfur odor emitted by algae as it breaks down in the ocean. DMS is a reliable indicator of the presence of krill, a primary food source for seabirds. Floating plastic debris provides an ideal platform for algae, and as the algae break down, the DMS odor lures seabirds into an "olfactory trap".
However, the ingestion of plastic by animals is not always due to its resemblance to food. Animals may unintentionally eat microplastics along with their food. For example, filter feeders like oysters, scallops, and mussels eat algae off floating microplastics, thereby consuming the plastic as well. Plastic can then travel up the food chain from these filter feeders to larger predators.
Animals may also be attracted to plastic because it smells like food. A study by Matthew Sovaca of the University of California, Davis, found that DMS is the "keystone infochemical" that drew marine animals to plastic as if it were krill. Odor extraction tests confirmed that common varieties of plastic acquired a DMS signature in less than a month.
Some animals may also be attracted to plastic due to its appearance. Brightly colored plastic may be more likely to attract hungry animals than other types of marine debris. Additionally, deep-diving toothed whales, such as sperm whales, may mistake plastic trash for food due to its similar echolocation signature.
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Animals eat plastic accidentally
Another critical factor contributing to accidental plastic consumption by animals is its odour. A recent study identified dimethyl sulfide (DMS), a stinky sulfur compound emitted by algae as it breaks down in the ocean, as the "keystone infochemical" that attracts marine animals to plastic. Algae thrive on floating plastic debris, and as the algae break down and release DMS, seabirds, in particular, follow their noses in search of krill, a primary food source, and end up trapped in an "olfactory trap." This helps explain why seabirds are especially vulnerable to plastic consumption, with virtually all of them having ingested plastic, according to an Australian study.
The physical characteristics of plastic also make it more likely to be accidentally ingested by animals. Many plastics float, break into small pieces, and are colourful, making them more attractive to hungry animals than other types of debris. Additionally, plastics can carry and absorb harmful pollutants and chemicals from the surrounding water, which can then be released back into the environment or transferred up the food chain as smaller animals are eaten by larger predators.
The consequences of animals accidentally eating plastic can be dire. Plastic can block their gastrointestinal tract, causing chronic hunger, intestinal injuries, and even death. It can also weaken animals, making them more susceptible to other threats. In some cases, plastic may pass through the digestive system, but it can still have detrimental effects on wildlife, including reducing the amount of actual food consumed during feeding dives and potentially transferring plastic and associated toxins up the food chain.
While the exact reasons why animals eat plastic are still being studied, the impact of plastic pollution on wildlife is undeniable. With billions of pounds of plastic entering our oceans each year and over 200 animal species documented to consume plastic, finding solutions to reduce plastic pollution and protect vulnerable species is of paramount importance.
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Plastic is mistaken for prey
Marine animals often mistake plastic for prey. Seabirds, for example, are attracted to flimsy, clear plastic bags that resemble jellyfish. Other marine animals, including fish, eat rice-sized microplastics that have been broken down by sunlight and wave action because they look like small particles of food.
A study by Matthew Sovaca, a doctoral student at the University of California, Davis, found that the smell of plastic, which is similar to that of food, also plays a role in marine animals' consumption of plastic. As algae break down in the ocean, they emit a sulfur odor known as dimethyl sulfide (DMS), which seabirds associate with krill, their primary food source. Floating plastic debris provides a platform for algae to thrive, and as the algae break down, they release the DMS odor, attracting seabirds in search of krill.
In addition to visual and olfactory cues, some animals may be attracted to plastic due to auditory cues. Deep-diving toothed whales, such as sperm whales, pilot whales, and beaked whales, use echolocation to hunt for food, typically squid. It is possible that these whales mistake plastic trash for prey based on the sounds it produces.
The ingestion of plastic by animals can have serious health consequences. Plastic can block the gastrointestinal tract, causing starvation, or release harmful chemicals into the body. It can also carry pollutants that are absorbed by animals and transferred up the food chain, affecting larger predators and even human seafood eaters.
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Plastic travels through the food web
Animals, including fish, turtles, whales, seals, birds, and camels, have been found to consume plastic. This happens because plastic may resemble food in appearance or smell. Seabirds are especially at risk, with virtually all seabirds having consumed plastic, according to a study by Australian scientists.
Once plastic is consumed by animals, it can block their gastrointestinal tract, causing starvation and death. In other cases, plastic is ground into small pieces in the stomach and then scattered. This process is known as "trophic transfer" of microplastics, and it allows plastic to move through the food chain. For example, nanoplastics in algae are eaten by water fleas, which are then consumed by fish.
Microplastics can also enter the human food chain through contaminated foods such as seafood, honey, sugar, salt, alcohol, bottled and tap water, and even from the air. In fact, the US population is estimated to consume 39,000 to 52,000 microplastic particles per year. These microplastics can carry toxins and chemicals, which can accumulate in animal fat and tissue through bioaccumulation.
The presence of microplastics has been observed in various organisms, including zooplankton, chaetognatha, ichthyoplankton, copepods, salps, invertebrates, and vertebrates. They are not easily broken down and tend to build up over time. This accumulation of microplastics can disrupt the natural balance in the environment and endanger animal life, the food chain, and public health.
To reduce plastic in the food chain, it is important to properly dispose of plastic waste, support local organizations working towards this goal, and spread awareness through social media.
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Frequently asked questions
Animals may mistake plastic for food because of how it looks or smells. For example, sea turtles often mistake clear plastic bags for jellyfish. Seabirds are especially at risk as they rely heavily on their sense of smell to find food. A recent study identified DMS (dimethyl sulfide) as the "keystone infochemical" that draws marine animals to plastic as if it were krill.
Plastic can cause intestinal injury and death, and it can also transfer up the food chain to bigger fish, marine mammals, and humans. It can also cause a chronic, unrelenting hunger or lethargy, eventually leading to starvation.
To stop animals from eating plastic, we need to reduce plastic pollution, especially in the oceans. Individuals can do their part by making sustainable choices in their daily lives and raising awareness about the problem.
