Microplastics in the ocean

In recent years, news such as "the ocean is polluted by microplastics, can seafood be eaten" and "microplastics are also contained in salt" have been frequently reported in the media. What is microplastics? Is eating seafood the same as eating plastic?

Microplastics in the ocean

Plastic is a general term for a large class of synthetic polymer materials. Because they have the advantages of light weight, waterproof, cheap, plastic shape, more durable, and colorful colors, they have been deeply integrated into all aspects of our daily life since the birth of the industrial revolution in the early 19th century. However, while it provides convenience for people, it also brings "white pollution" to the environment.

In order to curb the expansion of "white pollution", on June 1, 2008, my country began to implement the "plastic restriction order" to "brake" the unlimited use of plastic bags, causing many consumers to change their habits. For example, plastic bags are reused many times, or cloth bags or baskets are used instead. However, with the rapid development of e-commerce and express delivery industry, "online shopping" has become a new lifestyle, and disposable plastic consumables such as packaging bags, tapes, and anti-collision foam pads have ushered in a rapid increase. According to the 2018 data released by the State Post Bureau, the total business volume of the national express service industry has completed 50.71 billion pieces. It is not difficult to imagine that the number of plastic products involved in these express delivery must be an astronomical number.

So, where did all the plastic garbage we discarded go?

Will not disappear out of thin air

In 1997, the American Charles Moore (Charles Moore) discovered a large amount of floating garbage for the first time in the North Pacific Circulation Zone (located between the coast of Hawaii and the west coast of the United States), including beverage bottles and plastic bags printed in Chinese and Japanese. Common daily-use plastic products pollute an area of 2.5 million square kilometers, equivalent to 150 Hawaiian islands. After a lapse of 14 years, Moore's team once again found plastic waste widely distributed on the sea surface in the South Pacific Circulation Zone (located between Australia, New Zealand and the west coast of South America). The difference is that these plastic garbage floating on the sea surface have become plankton-sized microplastics, which are almost imperceptible to the naked eye. The same situation also appeared in the Atlantic circulation belt, the Indian Ocean circulation belt and the Arctic Ocean circulation belt.

It turns out that for those plastic garbage that "disappeared" from our lives, except for part of it is recycled, landfilled or incinerated, the rest has entered the ocean. Under the action of ocean currents, monsoons, tides and other external forces, large and small garbage debris drifts from the offshore to the open sea, and transfers from the ocean surface to the ocean abyss.

The degradation of plastics is essentially the process of breaking the long chains of high molecular polymers. After the plastic enters the water body, it is fragmented and degraded under the effects of ultraviolet radiation, wave hitting, biological habitat, and freeze-thaw cycles, and the particle size gradually becomes smaller, forming a huge number of microplastics. A lot of evidence shows that the process of forming microplastics from large plastic fragments is faster, while the process of microplastics degrading to smaller particles until mineralization is extremely slow. This means that the impact of microplastics is cumulative.

Microplastics in the ocean

As early as 2004, British scientist Richard Thompson (Richard Thompson) referred to plastic particles or fragments with a particle size of less than 5 mm as "secondary microplastics", and correspondingly, "primary microplastics", which refers to specially made Industrial products of tiny plastic particles. If some cosmetics are added with "scrubs" that enhance the cleaning ability, they are microplastic particles, which are washed into the sewer once they are used. Similarly, after washing clothes, we can always find a large amount of thread in the filter pocket of the washing machine. In fact, most of them are polyester fibers in the clothes. Those polyester fibers that are not captured are directly flushed into the sewer. According to statistics, at least 1,900 plastic fibers are produced every time laundry is washed. However, the current urban sewage treatment systems mostly use traditional treatment processes, usually equipped with 2-15 mm aperture grilles to mechanically clean the sewage, which cannot effectively treat the smaller microplastic particles and synthetic fibers. Therefore, a large amount of microplastics could not be removed and directly discharged into rivers and into the ocean.

Although research work related to marine microplastics had been carried out as early as the 1970s, people did not pay enough attention to this small particle size pollutant. In recent years, as scientists have successively discovered microplastics in water bodies and sediments in many sea areas, people have realized that microplastic pollution has become a global environmental problem. In addition, in inland areas far from the ocean, people have also found traces of microplastics in soil, rivers and lakes. From this point of view, microplastic pollution is like PM2.5 particles in the air, no one can stay out of it.

Alarm bells repeatedly

It is estimated that there are currently 150 million tons of plastic in the ocean, and this value is still increasing at a rate of 8 million tons per year, meaning that 15 tons of plastic garbage are dumped into the ocean every minute. If it continues to develop at the current rate without control, it is estimated that by 2050, the total weight of plastic waste in the ocean will exceed the total weight of fish resources.

Although a large amount of plastic waste enters the ocean through various channels every year, as we have seen, the ocean surface is not covered with a layer of plastic waste. Over time, some plastic waste will even "disappear" from the surface of the ocean. This phenomenon has also been confirmed by scientists. Kara Lavender Law, a professor of oceanography at the Woods Hole Oceanographic Institution in the United States, conducted a survey of plastic-rich areas in the Northwest Atlantic Circulation Zone. The results showed that plastic waste in the surface waters of the area was between 1986 and 2008. Did not increase significantly.

The vertical distribution of plastic in the ocean is also related to its density. The density of common plastics is mostly lower than that of fresh water or sea water, such as low-density polyethylene, high-density polyethylene, and polypropylene floating in water. And polystyrene and polyvinyl chloride will sink in water.

Even the microplastic particles floating on the surface of the ocean, their position in the water body is not static. Marcus Eriksen, an American environmentalist who focuses on the study of plastic pollution worldwide, believes that the surface of microplastics is prone to attaching microorganisms and plankton, and the hydrophilic "biofilm" will increase. The density of large and micro plastics gradually decreases to the bottom of the ocean.

In fact, the impact of microplastics on the ocean goes far beyond the pollution and destruction of the environment itself, and it also has a huge impact on marine life. Even Sagitta, which is only 1 to 2 cm in size, can ingest microplastics, which can cause serious effects. Richard Kirby, a plankton biologist from the United Kingdom, captured the scene of arrow worms eating microplastics for the first time. In fact, this phenomenon of plankton ingesting microplastics is very common. Because plankton plays an important role in the ecosystem, this phenomenon means that microplastics can be passed up level by level through a food web composed of multiple food chains.

Microplastics in the ocean

Organisms ingesting fluorescent microplastics: 1. Copepods ingesting 7.3 micron polystyrene beads (back view), 2. Copepods ingesting 20.6 micron polystyrene beads Flea (side view),/3. Early bivalve larvae ingested 7.3 micron polystyrene beads, 4. Decapod crab larvae ingested 20.6 micron polystyrene beads (side view), 5. Ingestion 30.6 micron decapod porcelain crab larvae (side view), 6. 30.6 micron polystyrene microbeads in the dorsal intestine of the long-horned water fleas, 7. 1.4 micron polystyrene microbeads stacked between the cilia of the tail fork Beads, 8. 30.6 micron polystyrene microbeads in the feces of Daphnia longhorni. (Source: Cole et al. EnvironmentalScience & Technology, 2013)

Microplastics have also been detected in salt

It is precisely because of a large amount of research evidence that microplastics are transferred layer by layer in the food chain (web), people have begun to pay attention to the problem of human ingestion of microplastics.

In October 2015, the research team of Professor Shi Huahong from East China Normal University published a paper in the journal Environmental Science & Technology. It mentioned that microplastics were found in edible salt from multiple brands and sources. The content of microplastics in sea salt is 550-681/kg, lake salt is 43-364/kg, and well salt is 7-204/kg. The comparison shows that the content of microplastics in sea salt is the highest.

After this result was reported by some media, it caused panic in the society for a while. Some people are beginning to worry about their own salt shakers, and some media even use the title "Eating salt is equal to eating plastic" to attract attention.

This experiment is actually tested in accordance with internationally accepted methods. After the salt sample is fully dissolved, it is filtered through a nitrocellulose membrane with a pore size of 5 microns (1 micron = 1/1000 mm). After drying at room temperature, the particles on the filter membrane are observed. First, observe the physical characteristics of plastic particles such as color and shape with an optical stereo microscope, and then randomly select some particles, and measure the spectrum with a micro-Fourier transform infrared spectrometer to determine the composition.

Microplastics in the ocean

The membrane pore size is 5 microns, and the membrane diameter is 47 mm. From the morphological point of view, microplastics are often in the form of small balls, flakes, fibers, and irregular pieces.

In fact, not only salt has fallen, but lobsters, shellfish, fish, honey, tap water, beer and other foods have all been detected to contain microplastics.

Although most seafood has been confirmed to contain microplastics, the amount of microplastics people consume when eating fish is less than that when eating shellfish. Because when we are cooking fish, we usually first remove the internal organs of the fish and discard them, and the microplastics in the digestive tract are also discarded. However, the microplastics in bivalve animals will still be ingested during people's consumption of shellfish. In October 2018, Philipp Schwabl, a medical scientist at the Medical University of Vienna, Austria, collected stool samples from 8 volunteers (3 males and 5 females, 33 to 65 years old) from different European countries and Japan. Microplastics were detected in. The investigation revealed that they had eaten food packaged in plastic bags a week ago, and 6 of them had also eaten seafood. These results show that the plastic garbage that was once thrown away by us has turned into "PM2.5" in the water, quietly returning to our side and even on our body.

What are the hazards of microplastics?

Many experiments have confirmed that microplastics can be ingested by organisms. In addition to reducing the feeding efficiency of organisms, lack of energy, injury or death, scientists have found in the laboratory that the intake of microplastics can cause toxic effects on organisms, including poor growth and development, reduced reproductive capacity, behavioral activities and Abnormal gene expression and reduced survival rate. When the particle size is further reduced, the microplastics in the digestive tract of marine organisms may pass through the intestinal epithelial cells and transfer to the circulatory system, immune system and even tissue cells through the digestive tract, triggering an inflammatory response in the body's immune system. However, the actual water environment is often difficult to reach the high-concentration exposure conditions in the laboratory. In most cases, although organisms ingest microplastics, there will be no related toxic effects in the short term.

But there are also small particulate matter no less than microplastics in nature, such as fly ash, diatom fragments, clay minerals, etc. Why only microplastics are listed as a key target? This is because microplastics are not only small in size and large in specific surface area, but also because of the nature of polymer compounds that determine their strong surface hydrophobicity and are easy to interact with pollutants, especially organic pollutants, in the environment. Microplastics can accumulate pollutants millions of times the environmental concentration from the environment. When they are ingested by organisms, under certain conditions, these exogenous pollutants will be desorbed from the microplastics and enter the digestive tract. Biological tissue absorbs and causes toxic effects. At the same time, in the plastic production process, flame retardants, plasticizers and other substances added in order to improve its special properties may also be released into the environment after weathering, which will adversely affect the health of organisms.

Philip Schwab’s research confirmed that people swallow microplastics into their stomachs in their daily lives. He also said that because these microplastics are large enough, they will not enter other tissues through intestinal epithelial cells, but It is directly excreted out of the body. A report from the United Nations Food and Agriculture Organization (FAO) in 2017* also believes that for rodents and dogs, microplastics with a particle size greater than 150 microns will not be absorbed and will be excreted through feces. If the human body ingests microplastics, 90% of them will eventually be excreted through the digestive system and may not cause harm to the human body.

However, due to the complex structure of the human digestive tract, microplastics cannot be completely excreted from the body, and a small part of them may be accumulated inside the human body. When the particle size is less than 20 microns, there is still the possibility of entering the blood circulatory system. On the other hand, "whether the internal environment of the human digestive system will aggravate the release of toxic substances in microplastics" is still unclear, and scholars need to further study.

As far as the environment is concerned, current research has confirmed that microplastics can cause changes in species diversity and indirectly destroy the balance of ecosystems. The most direct example is the report by L. Chapron and others in the Scientific Reports in 2018 that they were in the 540-meter-deep Raqqa-Dhière in the northwestern Mediterranean Sea ( Lacaze-Duthiers canyon) studied the effects of bulk plastic and microplastics on the growth of a cold-water stony coral Lophelia pertusa. The results prove that both large pieces of plastic and microplastics can cause the decline of coral calcification rate, and they interfere with the normal predation of coral insects and hinder their energy acquisition and distribution. This phenomenon has significantly slowed down the growth of coral skeletons and seriously threatened the accumulation of coral reefs. If things go on like this, it may cause a devastating blow to the coral reef ecosystem.

This article is excerpted from "Science World" Issue 3, 2019