Microplastic in aquatic systems | Technology Org

We live in the Plastic Era. Synthetic materials are almost everywhere. They can be found in medicine, pharmacy, automotive industry, cosmetics, and even in food. Slowly plastics became our “natural everyday environment.” Why?

Synthetic materials are lighter than glass, so it became the most common packaging material. Unfortunately, plastic is used in larger amounts than recycled due to human activity, making it easier for the environment. The ocean is full of this material also in the microplastic form. Once it gets to the aquatic systems, it stays there for a long time and affects living organisms. To some extent, it starts to form an entirely new ecological niche – Plastisphere. Within this article, we focus on the microplastic in the Big Blue waters.

Image credit: Agnieszka Pregowska & Science Embassy

Plastic-elastic-not fantastic

Plastics are synthetic materials made of polymers from many different chemical compounds that can be molded into shape. Depending on the chemical composition, they can be soft or set into a slightly elastic or rigid form. There are many materials that are commonly called plastics, but before we focus on them, let’s talk about polymers. In general, it is a group of chemical compounds that can be compared to the long chains in which particular cells are connected together.

When the material is made of polymer, it is made of repeating chains of molecules. Nature created many natural polymers that we use in everyday life. Cellulose is a polymer used to make paper; gelatin is used to make jelly-bears, silk, or wool is also made of natural polymers. Even our own DNA is a polymers [1]. Their list is so long that we cannot even imagine.

What about synthetic polymers? The group of man-made polymers that we are going to talk about is thermoplastics. These are materials that soften and melt at elevated temperatures. However, as soon as they cool down, they quickly harden again [2]. They are used in house-hold applications and are very popular even for toy manufacturing.

Polyethylene (polymer made of repeating ethylene molecules), commonly known as PET, can be found in plastic bottles, sealing foil, and many other food-packaging products. The next one is polypropylene (propylene molecules form a chain-like structure) that is widely applied in pipes, plastic boxes, and even bottle caps [3].

Microplastic poses a growing concern in oceans and other aquatic habitat. Image by 5Gyres, courtesy of Oregon State University via Flickr, CC BY-SA 2.0

Another example is polystyrene (styrene molecules make a polymer) that is the primary component of styrofoam used for insulating concrete forms, egg packaging, and even beanbags [4]. These are just a few examples of thermoplastics. There are also some other types of polymers, like duroplastics, which cannot be melted again after shaping [5]. Once they are melted, they remain solid. Thus they are rather not used for plastic bags and packaging.

The main advantages of these polymers are longevity and resistance, which become their major drawback when it comes to disposable materials. Although used just once, they are still durable and persist for ages in the oceans – their ultimate sink. The most common in Blue Waters are currently: polypropylene, polyethylene, and polystyrene.

Microplastic

While plastics have good elastic properties and can be easily taken in various types of shape, it is eagerly applied even in clothes [6]. Their global production is much higher than the recycling level, which generates tremendous pollution, especially in aquatic reservoirs. In turn, large plastic objects like plastic bags or bottles and great “sailors” like straws or toothbrushes are not the only problem that we struggle with when thinking about the Big Blue.

Why the ocean? The main mode of transport for plastics into the environment is water [7]. First of all, the synthetic materials are mechanically fragmented into smaller pieces. They also undergo degradation when exposed to UV radiation. So, when the common single-use plastic bags do not undergo biodegradation are fragmented, these small pieces flow in the water for a very long time. Moreover, their surface is covered with many microorganisms that are commonly called plastisphere when they live on the surface of plastics.

Did you know that wearing clothes made of synthetic fibers generate pollution of water? While doing laundry, a whole lot of synthetic microfibers are released into the water [8]. As for plastic particles from roads and cities, they are washed away by rain. Unfortunately, sewage treatment plants are not able to catch such small pollutants, and the vast majority of them end up in rivers and further into seas and oceans.

What about other fields? No matter what kind of plastic is used for, let’s say, food packaging, the pieces of plastic that have a size below 5 mm are called microplastic [9]. Recently, these tiny plastic pieces became a serious, global problem. It can be found everywhere on Earth. It was even found on Mount Everest as well as in the Antarctic regions [10]!

Harmful chemical compounds

No one needs to be told about the toxicity of synthetic materials. Thus, synthetic materials are not made only with polymers. They are full of plasticizers, pigments, flame retardants, and many other chemical compounds that can be toxic.

When the plastics are mechanically damaged and form small microplastic pieces, they release easier such harmful substances into the environment. The first are polycyclic aromatic hydrocarbons (PAH) that have a negative influence on living organisms [11]. They are rarely found as sole pollutants in the environment, which means that high concentrations of one compound from this group are equivalent to high levels of the others.

It is also worth mentioning plasticizers, e.g., phthalates, which are used as additives to improve the physical and chemical properties of plastics. They are suspected of influencing a higher incidence of asthma, allergies, and even mental disorders [12]. That is not the end of toxic chemicals.

Some plastics can release compounds like organotins. They are compounds that are used as catalysts in the production of silicone sealants, polyesters, and polyurethanes, and as biocides [13]. It is often found in inflatable bath toys but is also added (as a germicide) in the manufacture of plastic footwear (flip-flops) and sports and functional clothing.

Depending on the type of compound, they are toxic and lead to numerous disorders – mainly of the immune and nervous systems [14]. The next compound that can be released into the environment is bisphenol-A. That molecule is well-known for its neurotoxicity and endocrine disruption [15]. Once it affects the organisms, the health consequences can be serious. There are so many chemicals that can be released from microplastic into the environment that it is even difficult to count them.

Unfortunately, the scale of the problem is larger than we can even imagine. Microplastic have already been found in all kinds of marine organisms and plankton, invertebrates, fishes, birds, and even mammals [16]. It is known to accumulate in food chains.

Ingestion of microplastic by living organisms, especially those of smaller size, can lead to gastrointestinal lesions, tissue inflammation, liver stress, tumor formation, and endocrine disruption [4]. Because plankton forms the basis of marine food chains, threats to them can have serious and enormous consequences for the entire ocean.

The impact of microplastic on terrestrial organisms is still largely unexplored. However, there is growing evidence that it can act on organisms such as soil invertebrates, fungi, and plant pollinators. Due to its occurrence in the environment and various interactions with living organisms, microplastic may pose a growing global threat to ecosystems. [5]

Did you know that?

  • Microplastic is found everywhere, including in drinking water.
  • It was detected in the rain over the Rocky Mountains.
  • Microplastic is used to make glitter, toothpaste, and sunscreen.
  • A WHO report shows that according to some studies, bottled water contains more microplastics than tap water, which can also have microplastics seeping into it.

Summary

Since the first application of plastics in everyday life and their growing popularity, they became so commonly used and that we cannot imagine living without them. All we knew two decades ago was the fact that fossil-derived plastics need a few hundred years to degrade. Now we know that we pay the highest price, the health, for the use of plastics.

Fragmented pieces of plastics like microplastics easily get to the soil and water where release many chemical compounds that are harmful to living organisms. That is not the worst news! The microplastic can also be fragmented into smaller pieces having even nanometric size. They, they easily cross biological barriers and have devastating and yet unknown details influence on health, while that is the story for another time.

This article is a joint work of Oliwia Raniszewska (Faculty of Chemistry, University of Warsaw), Emilia Cywińska (Faculty of Chemistry, University of Warsaw), Agnieszka Pregowska (Institute of Fundamental Technological Research, Polish Academy of Sciences), Agnieszka Dąbrowska (Faculty of Chemistry, University of Warsaw), and Magdalena Osial (Faculty of Chemistry, University of Warsaw) as a part of the Science Embassy project. Image Credit – Agnieszka Pregowska $ Science Embassy

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[11] Lisbet Sørensen, Emilie Rogers, Dag Altin, Lurgi Salaberria, Andy M.Booth (2019) Sorption of PAHs to microplastic and their bioavailability and toxicity to marine copepods under co-exposure conditions https://www.sciencedirect.com/science/article/pii/S0269749119346408 [accessed 12 Feb. 2021]

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[13] Hamdy A. Hassan, Somya E. Dawah, Mostafa M. El-Sheekh, Monitoring the degradation capability of novel haloalkaliphilic tributyltin chloride (TBTCl) resistant bacteria from butyltin-polluted site, Revista Argentina de Microbiología, 10.1016/j.ram.2017.12.002, 51, 1, (39-46), (2019).

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