Microplastic is found everywhere in the sea, from the beaches to the shallows to the deep sea. It is eaten by numerous marine animals, including the fish and shellfish we eat (Kühn et al. 2015).
A Japanese research team has reported that plastic has been found in the digestive tract of Engraulis japonicus, a species of sardine that is dried and boiled before being eaten (Tanaka & Takada 2016).
The research team investigated the digestive tracts of 64 Engraulis japonicus 10 cm in size that were caught in Tokyo Bay. They found that 49 of them, or about 80%, had a total number of 150 pieces of microplastic in their digestive tract, with 2.3 pieces on average (Tanaka & Takada 2016).
Among these 150 pieces, 80% were between 0.1 and 1 mm (Tanaka & Takada 2016).
This is not only true for Engraulis japonicus in Japan. Microplastic is accidentally eaten by various kinds of edible fishes (Anastasopoulou et al. 2013, Foekema et al. 2013, Lusher et al. 2013, Collard et al. 2017, Collard et al. 2015, Romeo et al. 2015, Romeo et al. 2016, Neves et al. 2015).
In Europe, the very popular edible fish species living in the English Channel, such as herring, sardine, anchovy, mackerel, whiting, John Dory, gurnard, and flounder, were found to have pieces of plastic inside them (Lusher et al. 2013, Collard et al. 2015, Collard et al. 2017).
In the North Sea and Baltic Sea, pieces of plastic were also found in the digestive tracts of herring, mackerel, cod, haddock, and flounder (Foekema et al. 2013, Rummel et al. 2016), while on the Portuguese coastline, plastic was also found in 26 kinds of edible fish (Neves et al. 2015).
According to research on fish purchased at markets in the US and Indonesia, 1 in 4 fish (25%) were reported to have either pieces of plastic or fibrous plastic in their digestive tract (Rochman et al. 2015).
It is thought that filter feeding fish (planktivores) such as herring, mackerel, and sardines eat microplastics that are mixed with plankton.
On the other hand, fish like cod eat invertebrates, such as shellfish, living at the bottom of the sea. They may eat the invertebrates and plankton that have eaten plastics. This is called the secondary consumption of plastic.
The secondary consumption of plastic also happens when fish that have eaten plastic are themselves eaten. In the Mediterranean Sea, large types of migratory fish, such as swordfish, Atlantic bluefin tuna, and albacore tuna were investigated; 20% were found to have plastic in their digestive tract (Romeo et al. 2015).
However, most of the tiny microplastics, less than 1 mm, may contain various toxic substances, such as the additives that are added when plastic products are made, endocrine disruptors that have been absorbed from seawater, etc. (Rochman 2015).
An Italian research team has reported that contaminated substances that stick to microplastic affect the health of fish (Pedà et al. 2016) in an experiment using European sea bass. First, they prepared microplastics made of PVC. They also prepared microplastics that had been soaked in a contaminated area of the ocean and had them absorb toxic substances. Then, they gave these two types of microplastic to the fish.
The result was clear. Both the fishes that had ingested intact microplastics and contaminated microplastics were found to have moderate to severe deformation at the bottom of the intestine after 60 to 90 days (Pedà et al. 2016).
It is said that people around the world eat an average of 20 kg of fish in a year, while 17% of protein consumption is supported by seafood (FAO 2014). Therefore, it is very likely that plastics are accidentally being eaten by humans as well.
We usually don’t eat the guts of the fish and, therefore, we may seldom directly eat microplastic. However, we sometimes eat small fish whole, while the chemical substances that have transferred from the plastic to the fat of the fish cannot be avoided.
Even so, we still don’t know the exact impact on our health that results from eating microplastic with our seafood. It is crucial that further studies are made (Lusher et al. 2017).
But this is the food we eat. No matter how much we worry, it is not enough.