Characteristics and Seasonal Distribution of Microplastics in the Surface Waters of Southwest Coast of the Caspian Sea (Guilan Province, Iran)

Assessing Chlorophyll-a Variations in Caspian Sea during the COVID-19 Pandemic

The COVID-19 pandemic's disruptions to human activities prompted serious environmental changes. Here, we assessed the variations in coastal water quality along the Caspian Sea, with a focus on the Iranian coastline, during the lockdown. Utilizing Chlorophyll-a data from MODIS-AQUA satellite from 2015 to 2023 and Singular Spectrum Analysis for temporal trends, we found a 22% Chlorophyll-a concentration decrease along the coast, from 3.2 to 2.5 mg/m³. Additionally, using a deep learning algorithm known as Long Short-Term Memory Networks, we found that, in the absence of lockdown, the Chlorophyll-a concentration would have been 20% higher during the 2020-2023 period. Furthermore, our spatial analysis revealed that 98% of areas experienced about 18% Chlorophyll-a decline. The identified improvement in coastal water quality presents significant opportunities for policymakers to enact regulations and make local administrative decisions aimed at curbing coastal water pollution, particularly in areas experiencing considerable anthropogenic stress.

Abundance and risk assessment of microplastics in water, sediment, and aquatic insects of the Nile River

Microplastics (MPs) are a serious threat in freshwater environments. The ecological risk and abundance level of MPs in abiotic and biotic compartments of the Nile River haven't been systematically reported. Thus, these issues were highlighted in the present study during different seasons of the sampling year. The results showed that MP concentrations in the river ranged from 2.24 ± 0.6 to 3.76 ± 1.1 particles/L, 298 ± 63 to 520 ± 80 particles/kg dry weight, and 0.081 ± 0.051 to 4.95 ± 2.6 particles/individual in surface water, sediment, and different species of aquatic insects, respectively. All the extracted MPs are colored blue, red, and black. Fiber-shaped polyesters (<500-1500 μm) were the most common MPs in all the river compartments. MPs' dominance was observed during the summer in comparison with that in the other seasons. Environmental risk indicators indicate the high ecological risk of MPs, which are widely distributed in the Nile River. In conclusion, MP consumption by aquatic insects may not only be related to levels of environmental contamination, since other variables, such as taxon size, weight, and particular feeding behavior, may also be significant. Additionally, the presence of MPs in insects (at lower trophic levels) creates the potential for predation-based inter-trophic level transmission. Thus, higher trophic-level investigations of various feeding groups should be carried out to identify any possible harm that MPs cause to various aquatic organisms.

Microplastics abundance, distribution and composition in surface waters, sediments and fish species from Amir-Kalayeh Wetland, Northern Iran

Microplastics (MPs) pollution is considered as a globally pervasive threat to aquatic ecosystems and many studies reported this pollution in different aquatic ecosystems. However, studies on MPs pollution in wetlands are still scarce. Therefore, the aim of present study was to investigate the presence of MPs in the surface water, sediment and different fish species of Amir-Kalayeh wetland, Northern Ian. Surface water and sediment samples were collected from six stations during June to July 2022. Moreover, the gills and gastrointestinal tract (GIT) of 54 fish specimens belonging to four species including Cyprinus carpio, Tinca tinca, Esox lucius and Silurus glanis were analysed. MPs were detected in all samples with an average of 2.15 ± 1.98 items/m3 for surface water, 51.66 ± 32.20 items/kg dry weight for sediments, 0.17 ± 0.17 items/individual for fish GIT and 0.12 ± 0.12 items/individual for fish gills. There was no significant relationship between MPs abundance in surface waters and sediments as well as between MPs abundance in environmental matrices and fish (P > 0.0.5). In terms of feeding habit, no significant differences were observed between the number of MPs found in omnivorous and carnivorous fish species (P > 0.05). Moreover, no significant relationship was detected between the MPs abundance in fish tissues and body size (P > 0.05). MPs were mainly fibers, mostly transparent, and in a range size of 70-5000 µm. The dominant MPs type was nylon in all samples. This study will help increase our knowledge about MPs pollution in inland freshwater systems and suggests that management policies take essential steps to reduce this insidious problem in freshwater ecosystems.

Interactions between microplastics and Culex sp. larvae in wastewater

Microplastics (MPs) are a growing issue because they endanger both aquatic organisms and humans. Studies have indicated that wastewater treatment plants (WWTPs) are one of the major contributors to MPs in the environment. However, studies on the abundance of MP contamination in WWTPs and its transmission into aquatic organisms are still scarce, especially in Egypt. The goal of this study was to examine the temporal fluctuations in the distribution of MPs in surface water and the dominant macroinvertebrate fauna (Culex sp. larvae) in a fixed wastewater basin in Sohag Governorate, Egypt. The average of MPs in the surface water was 3.01 ± 0.9 particles/L. The results indicated to seasonal variation of MP abundance in the wastewater basin that was significantly higher in winter than in the other seasons. The risk index for polymers (H), pollution load index (PLI), and potential ecological risk index (RI) were used to assess the degree of MP contamination. The basin has moderate H values (<1000) because of the presence of polymers with moderate hazard scores such as polyester (PES), polyethylene (PE), and polypropylene (PP). According to the PLI values, surface water is extremely contaminated with MPs (PLI: 88 to 120). The RI values of surface water showed higher ecological risk (level V). MPs in Culex sp. larvae were seasonally changed with an 85% detection rate, and an abundance average of 0.24 ± 0.65 particles/ind, MP concentration in Culex sp. larvae was influenced by the MP characters (shape, color, and polymer). The larvae of Culex sp. showed a greater preference for black and red fibrous polyester (PES) with sizes (<1000 μm) of MPs. These findings suggest that Culex sp. larvae prefer ingesting MPs that resemble their food. It is possible to overestimate Culex sp.'s preference for lower sizes because of their catabolism of MPs. To better understand the preferences of Culex sp. larvae for MPs, further controlled trials should be conducted. PRACTITIONER POINTS: Wastewater is highly contaminated with microplastics (MPs) in the different seasons. First report of detection of the seasonal abundance of MP in Culex sp. larvae. Culex sp. larvae showed a stronger feeding preference for MPs with specific characteristics. Smaller size and blue polyester fibers were the dominant characteristics of MPs in wastewater.

Analysis of microplastics in ships ballast water and its ecological risk assessment studies from the Persian Gulf

Transport of ballast water is considered a significant vector for dispersion of different pollutants, including microplastics (MPs), throughout the world's oceans. However, there is limited information on MPs in ballast water. Size distribution, polymer type, and ecological risks of MPs in ballast water were investigated for the first time in this study. The mean levels of MPs in ballast water and seawater samples were 12.53 and 11.80 items/L, respectively. MPs with a size category of 50-300 μm was the most abundant. Fiber, black, and polycarbonate (PC) were the predominant shape, color, and polymer type of identified MPs in ballast water and seawater, respectively. The pollution load index (PLI), hazard index (HI), and risk quotient (RQ) indicated high levels of MP pollution, potentially indicating an ecological risk. These findings increase our understanding of the major sources (such as ballast water), transportation routes, and related ecological risks of MPs to marine ecosystems.

Beadlet anemone: A novel bio-indicator of microplastic pollution in the marine environment

Extensive usage of plastic in different industries and household usage has degraded to microplastic due to environmental conditions over the last year. While several researchers conducted the determination of microplastic (MP) bioaccumulation from rivers to stormwater, except for some filter-feeding species used as a bioindicator, to achieve a holistic approach to the fate of MPs in the marine system, sea anemone was used as an indicator. Microplastics were extracted from surface seawater, sediment, and sea anemones from the same sampling area and characterized. The extracted MPs were confirmed by confocal micro-Raman spectroscopy, and the morphology of the MPs was investigated by scanning electron microscopy (SEM). The results showed that the accumulation of microplastics and the type of polymer, shape, colour, and size of these persistent pollutants varied in sediment, surface water, and sea anemone. The abundance of MPs was different, and grey-coloured MPs were detected at a relatively higher level in sea anemones, from 8.7 to 13.3%, and more minor MPs (less than 0.5 mm) at 43.4-56.8% were detected in sea anemones among the sampling stations. In terms of polymer type, there are relatively more types of polymers classified in sea anemones among the sampling stations (six different types of polymers). These results indicated that the utilization of sea anemones as a bioindicator for MPs could be a critical factor in a better understanding of their pathway in the marine ecosystem. This study proved that analysing sea anemones as an indicator could offer a reliable, fast, and time-saving approach for detecting microplastic accumulation in marine systems.

Seasonal variations of microplastic in sediment, Chironomus sp. larvae, and chironomid tubes in two wastewater sites in Sohag Governorate, Egypt

Microplastic (MP) contamination is an acknowledged global problem that poses a severe risk to aquatic ecosystem biota. Nevertheless, little is known about their prevalence in animal construction. The main objective of our study was to reduce the gap information of seasonal abundance, distribution, composition, and risk assessment of MP contamination. The concentrations of MPs in sediment, Chironomus sp. larvae, and their tubes were found to be higher in site 2 (S2) than in site 1 (S1) during the four seasons of the year. However, MP concentrations ranged from 312 ± 64.7 to 470 ± 70 items/kg dry weight, 0.79 ± 0.16 to 1.1 ± 0.3 particles/individual, and 0.5 ± 0.04 to 0.9 ± 0.04 particles/tube in sediment, Chironomus, and chironomid tubes, respectively. Blue and red polyester fibers are the most dominant MPs which are distributed in sediment, Chironomus, and chironomid tubes. The length of the dominant fiber accumulates in Chironomus, and their tubes are highly varied compared to that of the substrate. Additionally, we found that the mean number of MPs/individual larvae in the fourth instar was significantly higher than that in the second instar. Risk indicators for the environment, polymer risk assessment, and pollution load were estimated, where they were higher in S2 than in S1 correlated to MPs abundance and polymer type. The seasonal fluctuation in MP concentration, characterization, and risk in the two sites could depend on the amount of sewage effluent discharged into the wastewater treatment plants (WWTPs), which was reflected by Chironomus sp. larvae. Therefore, further research should be done to adopt the applicability of Chironomus as MP bioindicators in various freshwater environments throughout the world.

Microplastic Pollution in the Gastrointestinal Tract and Gills of Some Teleost and Sturgeon Fish from the Caspian Sea, Northern Iran

The increasing microplastic pollution in the marine environment has raised global concern. The main risk of microplastics in aquatic ecosystem is their bioaccumulation in aquatic organisms. A few studies have reported microplastic pollution in the digestive system of Caspian Sea fish species, but there is no research on sturgeon species, nor on fish gills. We investigated the occurrence of microplastics in the gastrointestinal tract (GIT) and gills of 62 specimens belonging to four species including three teleosts (Cyprinus carpio, Rutilus kutum, and Chelon aurata) and one sturgeon (Acipenser persicus, a valuable endangered species) from the Caspian Sea between January and March 2022. Fish tissues were removed, exposed for 24 h to 10% KOH, and then dried on filter paper. Particles were observed under a stereomicroscope and analyzed by Raman microspectrometry, scanning electron microscopy, and energy-dispersive spectroscopy. A total of 91 microplastics were detected in the GIT (average of 1.46 ± 1.17 items/individual) and 63 microplastics in the gills (average of 1.01 ± 0.62 items/individual). A significant correlation was not found between the number of microplastics found in both tissues and fish body length, body weight, GIT weight, and gill weight (p > 0.05), except between microplastics isolated from gills and gill weight in C. carpio (rs  = 0.707, p = 0.022). The abundance of microplastics in fish followed the order of A. persicus > C. aurata > R. kutum > C. carpio. The microplastics were in the size range of 45 to 5000 µm, with particles of 300 to 1000 µm being the most prevalent; 74.68% of the particles were shaped like fibers, 30.53% were red, and 70.6% were composed of nylon polymer. Environ Toxicol Chem 2023;42:2453-2465. © 2023 SETAC.

Seasonal distribution of microplastics in the surface waters of the Yellow Sea, China

Different studies are filling the gaps in the distribution map of global marine microplastics. However, the data on the seasonal variation is relatively limited, which may lead to overestimation or underestimation of the distribution level of microplastics. To understand baseline data and seasonal variations of the microplastics in the surface seawater of the Yellow Sea, a survey over four seasons was conducted during 2017-2018. Microplastics were collected using a 330 μm manta net. It was found that the abundance of microplastics was 0.63 ± 0.57 particles/m³. The seasonal abundance variation was spring > summer ≈ winter > autumn. The main categories were foam, line, and fragments, accounting for 32 %, 19 %, and 19 % of the total amount, respectively, and the dominant components were polypropylene, polyethylene, and polyethylene terephthalate, accounting for 38 %, 22 %, and 22 % of particles, respectively. The factors affecting the variation included wind-induced mixing, river input, and environmental topography.

Occurrence and risks of microplastics in the ecosystems of the Middle East and North Africa (MENA)

The ubiquitous nature of microplastics (MPs) in nature and the risks they pose on the environment and human health have led to an increased research interest in the topic. Despite being an area of high plastic production and consumption, studies on MPs in the Middle East and North Africa (MENA) region have been limited. However, the region witnessed a research surge in 2021 attributed to the COVID-19 pandemic. In this review, a total of 97 studies were analyzed based on their environmental compartments (marine, freshwater, air, and terrestrial) and matrices (sediments, water columns, biota, soil, etc.). Then, the MP concentrations and polymer types were utilized to conduct a risk assessment to provide a critical analysis of the data. The highest MP concentrations recorded in the marine water column and sediments were in the Mediterranean Sea in Tunisia with 400 items/m³ and 7960 items/kg of sediments, respectively. The number of MPs in biota ranged between 0 and 7525 per individual across all the aquatic compartments. For the air compartment, a school classroom had 56,000 items/g of dust in Iran due to the confined space. Very high risks in the sediment samples (Erⁱ > 1500) were recorded in the Caspian Sea and Arab/Persian Gulf due to their closed or semi-closed nature that promotes sedimentation. The risk factors obtained are sensitive to the reference concentration which calls for the development of more reliable risk assessment approaches. Finally, more studies are needed in understudied MENA environmental compartments such as groundwater, deserts, and estuaries.

Microplastic-associated pathogens and antimicrobial resistance in environment

The ubiquitous use of microplastics and their release into the environment especially the water bodies by anthropogenic/industrial activities are the major resources for microplastic contamination. The widespread and often injudicious use of antimicrobial drugs or antibiotics in various sectors including human health and hygiene, agriculture, animal husbandry and food industries are leading to the release of antibiotics into the wastewater/sewage and other water bodies, particularly in urban setups and thus leads to the antimicrobial resistance (AMR) in the microbes. Microplastics are emerging as the hubs as well as effective carriers of these microbial pathogens beside their AMR-genes (ARGs) in marine, freshwater, sewage/wastewater, and urban river ecosystems. These drug resistant bacteria interact with microplastics forming synthetic plastispheres, the ideal niche for biofilm formations which in turn facilitates the transfer of ARGs via horizontal gene transfer and further escalates the occurrence and levels of AMR. Microplastic-associated AMR is an emerging threat for human health and healthcare besides being a challenge for the research community for effective management/address of this menace. In this review, we encompass the increasing prevalence of microplastics in environment, emphasizing mainly on water environments, how they act as centers and vectors of microbial pathogens with their associated bacterial assemblage compositions and ultimately lead to AMR. It further discusses the mechanistic insights on how microplastics act as hosts of biofilms (creating the plastisphere). We have also presented the modern toolbox used for microplastic-biofilm analyses. A review on potential strategies for addressing microplastic-associated AMR is given with recent success stories, challenges and future prospects.