**1. Introduction**

The oceans perform a vital function as a regulator of the climate and absorb 25% of the CO2 generated [1]. Through the production and consumption of foodstuffs, industrial and consumer goods, humankind produces large quantities of waste, whereof a considerable proportion ends up in the ocean sooner or later. Three-quarters of the waste in the ocean consists of plastic. This plastic is a steadily growing problem, costs the lives of ten thousands of animals every year and can also endanger humans.

Over 80% of the plastic material entering the ocean annually originates from landbased sources, which correlates with the fact that half of the world population lives in coastal regions [2, 3]. Large plastic waste represents the main contribution, including everyday objects like drink bottles and other types of plastic packaging. An estimated 4.8–12.7 million tons enter here annually [2]. The remaining input comes from plastic, which is released at sea, mainly from fishing—for example, due to lost and discarded fishing gear, which is estimated at 0.6 tons a year [4]. About 94% of the large plastic parts, which end up in the sea, sink with time to the ocean floor. Today, an average of 70 kg of plastic can be found on every square kilometer of the ocean floor.

Approximately, 350–400 years can pass before the plastic is completely degraded. As it moves through the seas, the plastic changes. Through weather conditions and waves, for example, it disintegrates into smaller and smaller fragments and from the macroplastic, the so-called secondary microplastics are formed [5]. If it directly enters the environment, it is designated as primary microplastics.

By definition, microplastics are small, solid, and water-insoluble plastic particles under 5 mm in size. In the meantime, these particles can be found in all bodies of water. They could even be detected in the Arctic [6].

 The input of primary microplastics is estimated at 0.8–2.5 tons a year [7]. This enters mainly through tire abrasion and textile fibers, which enter the wastewater through washing clothes and thus end up in the environment. But also the dust from the wear on road paint, microplastics used in personal care products, marine coatings, and lost plastic pellets are important entry routes (**Figure 1**).

 In general, a strong correlation can be observed between the population density and the microplastics concentration [8, 9] .The proximity to densely populated regions and poor waste management lead to particularly high levels of contamination [10, 11]. Sewage treatment plants or plastics manufacturing respectively processing companies are also important point sources and can release high volumes of plastic and microplastics locally (**Figure 2**) [12, 13].

**Figure 1.**  *Global release of primary microplastics to the world oceans [7].* 

*Technological Approaches for the Reduction of Microplastic Pollution in Seawater… DOI: http://dx.doi.org/10.5772/intechopen.81180* 

#### **Figure 2.**

*Microplastic inputs and transport paths into the ocean [7, 15].* 

Ports and industrial areas are especially contaminated with microplastic particles [14]. The majority of the microplastics remain near the shore [10]. In the Arabian Gulf along the coast, 4.38 × 104 –1.46 × 106 microplastic particles/km2 could be detected in the surface water [15].

 Off the coast of South Africa, there were 257.9 ± 53.36 to 1215 ± 276.7 microplastic particles/m3 of water [12]. At the mouth of the Yangtze in the East China Sea, 4137.3 ± 2461.5 microplastic particles/m3 could be detected, whereby the concentration in the open sea was only 0.167 ± 0.138 microplastic particles/m3 [13].

The most common polymer types occurring in seawater are, in addition to polyethylene, polypropylene, and polystyrene, also polyamide, polyester, polymethylmethacrylate, polyvinyl chloride, polyoxymethylene, polyvinyl alcohol, polymethylacrylate, polyethylene terephthalate, alkyd resins, and polyurethane [16]. They are found in descending prevalence in the seawater.

The quantification of the inputs into the environment is, as a rule, based on a loss rate, which is calculated against the produced quantity of preproduced plastic [17]. The categorization of the industries, which manufacture preproduced plastic, is organized in producers (manufacture plastic material from raw materials), intermediaries, converters (convert preproduced plastic into products, or individual components), external waste disposers, and shipping companies (transport the material). By means of the difference between the respectively processed plastic quantities and the loss rate, the plastic quantities, which are released into the environment by the plastics industry alone, are revealed.

Forecasts assume an increasing plastic production volume in the future, which will lead to an increasing entry quantity of plastic and microplastics in the environment and seas [2]. In addition, microplastics arise continuously through the constant fragmentation of plastic already in the environment [5]. This leads to an ever higher contamination of the marine environment with microplastics.

Since the current analytical methods to detect microplastic in the aquatic environment have numerous shortcomings [18], the contamination of the marine environment can only be estimated. Particularly problematic here is that small plastic particles cannot be captured in most monitoring cases. The lower detection limit in the marine environment is usually 300 μm. With increased efforts, the lower detection limit can be reduced to 20–10 μm [16]. However, this is seldom practiced. Particles below the detection limit are not captured. Additionally, studies are not readily comparable, since there is no standardized monitoring procedure [18].
