**5. Discussion**

Numerous studies were conducted around the world to characterize microplastic abundance in water, sediment, and biota. However, still the methodology and reporting unit is not yet standardized. Different sampling procedures for sediment can be found in the articles. For example, sample quadrat varies in the studies from 1 × 1 m to 0.3 × 0.3 m [34, 35], and the most common quadrat is 0.5 × 0.5 m. This is the case with sampling thickness in which some studies collect the sample from 5 cm [36] while others take only the top 1 cm [33, 36, 37]. Also, density separation fluid density varies from 1.2 g/ml for NaCl to 1.8 g/ml for NaI. In this study, NaCl was used since it is the most popular choice, easy to use, and low cost. Moreover, reporting units in the published papers are different such as particle/kg, particle/m2 , mg/g sediment, mg/m2 , and particle/0.0125m3 . Weight in some studies is presented as dry sediment weight, while in others is a wet sediment weight. Therefore, comparison between the results is not a straightforward process. Multiple published articles and review papers summarized the methodologies and results of many microplastic studies done around the world [38–40].

*Microplastic Contaminants in the Sediment of the East Coast of Saudi Arabia DOI: http://dx.doi.org/10.5772/intechopen.109019*

**Figure 5.**

*Spectrum for different shapes and colors of microplastic.*

Microplastic abundance per area was estimated in this study since part of the studies done in the Arabian Gulf described microplastic abundance as particle/m2 [33, 41]. To calculate the abundance in particle/m2 , equal vertical distribution along the 5 cm depth must be assumed. Also, it is important to clarify that the reporting unit is a particle of microplastic in an area of 1 m2 and at 1 cm depth. The results showed an average abundance of 112.5 particles/m2 for the low tide zone and 106.3 particles/m2 for the high tide zone.

Comparing microplastic abundance on the east coast of Saudi Arabia against worldwide countries shows that the Saudi east coast of the Arabian Gulf is among the least polluted coasts (5.5 to 21.2 particles/kg, 50.6 to 204.5 particles/m<sup>2</sup> ). Multiple studies with similar microplastic extraction procedure done on the southwestern side of the USA coast and at several European beaches [42, 43] shows a higher abundance of microplastic [42–44]. Same with Asian countries where microplastic abundance tends to be higher than our results [12, 45, 46]. **Table 2** summarizes some results of

various studies around the world taking into consideration similar methodologies and reporting units. Higher abundance in smaller particle sizes is also observed in most of the studies. Black and blue were the most common colors in these articles, and fiber is the common shape.

With regards to the gulf countries, a review paper by Saif Uddin et al. [38] summarizes all the studies carried out in the Arabian Gulf in terms of the type of samples, sampling methodology, and results. From the Iranian coast to the Oman sea through the Strait of Hormuz to Bander Abbas city beaches, studies show greater microplastic abundance compared to the Saudi east coast [36, 41, 47, 48]. This might be due to the geology of the area and the counterclockwise movement of the seawater [29]. In these studies, density separation was done using brine density higher than NaCl which led to extracting more microplastic particles. As stated by Naji et al. [49] in their study that around 74% of microplastic was extracted using NaCl, while the remaining 26% was recovered by NaI. However, the studies done in Qatar by Abayomi [50] and UAE by Aslam [33] used the KI solution for density separation and it shows much lower microplastic abundance than that of the Iranian coast. The results of both studies are comparable with this study's numbers and that gives more confidence in our methodology. This was also supported by the similarity in having fiber, blue, and PE as the most common properties of the collected microplastic.

Despite that the average of low tide and high tide abundance is very close to each other; it may vary a lot when compared site by site. The difference is observed in all the sites except Jubial which has the lowest abundance among all the sites. Low tide shows higher abundance in Dammam and Khafji samples while it was less in Salwa. Therefore, there is no trend between the high tide and low tide abundance which was also observed [47]. It was expected to have higher microplastic abundance in Dammam, Jubail, and Khafji since they are both crowded and industrial cities. However, Jubail shows a very low number which was unexpected for the biggest industrial city in the eastern region. Several reasons might cause these low numbers which are as follow:


On the other hand, Salwa which is considered a rural city showed high microplastic abundance and this also can be explained by the following reasons:


*Microplastic Contaminants in the Sediment of the East Coast of Saudi Arabia DOI: http://dx.doi.org/10.5772/intechopen.109019*

Since Salwa is located near the border of Qatar, it will be useful to compare its results with Abayomi's results [50]. Umm Bab sampling site is the closest one to Salwa beach, and it shows a microplastic abundance of 8.3 particles/kg which is similar to our results for Salwa average low tide (8.4 particles/kg) (**Figure 4**).

Microplastic with a size ≤2 mm was the most common size among the samples (77%). It is expected to have even smaller (<0.5 mm) microplastics that already passed the 0.5 mm stainless steel sieve. The smaller the microplastic particles are, the more vulnerable they became to a smaller organism. Based on a study done by Naji et al. [49], microplastics with sizes ranging from 0.02 to 1.68 mm were the most common size found in cyclopoids, shrimps, and zoea. Having microplastic induced in the organisms at the base of the food web could cause biomagnification in the bigger organisms that feed on them.

As mentioned before, around 96% of the collected particles were fiber. This result is similar to all the studies done in the Arabian Gulf and most worldwide studies (**Tables 2** and **3**). This could be due to disposing sewage rich in synthetic fiber released from textiles, or clothes into the sea [6, 57]. Degraded fishing ropes and nets are considered a source of microplastic fiber in seawater. Treatment of wastewater before disposing to the sea may remove more than 80% of the microplastic [58]. Unfortunately, some countries dispose of the wastewater without primary treatment [59] which may increase the microplastic fiber in the oceans. Microplastic fibers were found to be one of the most shapes to be ingested by zooplankton [33, 60, 61]. More studies also showed that microplastic fiber is the most ingested by turtles, fish larvae, and Mesoplodon mirus [62–64].

Transparent and blue colors like most of the studies in the area were the most common colors followed by black color (**Figure 6**). No significant change in color distribution was found among the sampling sites. The importance of quantifying microplastic color was described by Shaw et al. [65] research which shows that colored microplastic is more likely to be ingested by organisms as prey, and the white, transparent, blue, and black colors were the most commonly found [65]. During microscope analysis, some particles were found with a partially faded color. This indicates that some of the originally colored microplastic particles turned into colorless particles and that could be because of the physical or chemical reactions between the particles and the surroundings. The changing of color was also mentioned by Chen et al. [66] and by Wibowo et al. [67] which show that time is playing a role in changing the microplastic color and size.

Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) analysis shows that different colors of microplastic fibers had similar polymer types which are polyethylene terephthalate (PET). Since fiber was the most common shape (96%), then this suggests that PET is the most common polymer type in the collected samples. This result is consistent with the studies done in the Arabian Gulf, and most of the studies around the world. PET is commonly used in making ropes and drinking bottles which are heavily used in KSA specifically for water bottles. Fragments and filaments particle were identified as polyethylene (PE) and high-density polyethylene (HDPE). These polymer products are also commonly used in our daily life, such as bags and shampoo bottles. Only one particle was identified as polypropylene (PP) which was also reported in Qatar by Abayomi et al. [50]. This suggests that most of the microplastic contamination in Saudi east beach is coming from the daily used plastic product which reaches the sea through wastewater effluent, direct dumping of plastic into the sea, or run-off.


**Table 2.**

*Examples of microplastic studies around the world.*

*Advances and Challenges in Microplastics*

**176**


**Table 3.**

*Microplastic studies in the Arabian Gulf (sediment).*
