Microplastics (MP) are synthetic elements produced directly or indirectly by man, with sizes up of to 5 mm (^{Iannacone et al., 2019}; ^{Zhou et al., 2020}). There is currently more research on MP in marine ecosystems compared to coastal marine ecosystems, and even less in coastal wetlands (^{Ayala et al., 2021}). Therefore, it is of great importance to characterize and identify the environmental impacts generated by MP in wetlands (^{Reynolds and Ryan, 2018}; ^{Faria et al., 2021}).

In recent years, the presence of MP in protected natural areas in several Ibero-American countries is being evidenced (^{Mazariegos-Ortíz et al., 2021}). The Pantanos de Villa Wetlands (PVW), known locally as Los Pantanos de Villa, is a natural area protected by the Peruvian state and is an international RAMSAR site (^{Pulido-Capurro, 2018}; ^{Edo et al., 2020}). Wetlands can become MP sinks, which are preserved and accumulated continuously over a long period of time. Variations in the color, shape and size of MP can lead to their being mistakenly ingested by aquatic biota (^{Carlin et al., 2020}; ^{Valencia et al., 2020}). The presence of plastic garbage in PVW could be the first indication of MP generation, with an impact on resident and migratory birds that use plastics to build their nests (^{Blettler et al., 2020}).

RAMSAR wetlands are of great global importance for hosting a great diversity of life that is dependent on coastal marine ecosystems (^{Sruthy and Ramasamy, 2017}). It is important to characterize MP deposited in sediment and water of the PVW due to the impact on aquatic biota. Therefore, the objective of the present investigation was to characterize the MP in water and sediment of the PVW.

PVW is located in the district of Chorrillos, in the Province of Lima, Peru (Figure 1) (^{Pulido-Capurro, 2018}). Its waters correspond to underground outcrops, covering an approximate area of 263 ha located at 5 m above sea level (Pulido-Capurro, 2018). The Laguna Mayor is the object of study because it is the largest body of water within the PVW. This lagoon has an area of 50,000 m² and is adjacent to industrial and urban areas and paved roads (^{Alarcón and Iannacone, 2014}).

Sampling: Sampling was carried out from 6:30 a.m. to 6:45 p.m. during the winter season in September 2019 using a boat for four people (1.5 x 4.2 m). A Garmin 64s GPS (The Environment Management’s CEO, Kansas, USA) was used to locate the sampling points. At each point, a water sample and a sediment sample were collected. Between one point and another there was an approximate distance of 125 m. A total of 16 sampling points were established in the Laguna Mayor according to quadrants based on the recommendations and method used by ^{Yuan et al. (2019)}. Chairmaker’s bulrush (Schoenoplectus americanus Pers.) and southern cattails (Typha domingensis Pers.) covered and produced islets that appear to surround some areas of the lagoon evaluated. The 16 water and sediment sampling points (P) were divided into three sectors (A: P11-16, B: P4, 6-7, 9-10 and C: P1-3,5,8) (Figure 1).

Figure 1 Satellite image of the Laguna Mayor of PVW with the sectors and areas of possible direct influence of MP or solid waste. A. (P11-16). B. (P4, 6-7, 9-10). C. (P1-3,5,8). P = sampling points. 

Sector A was delimited by six areas (areas 4, 5, 6, 7, 8 and 9) and two vehicular routes (via 1 and 4). Areas 4 and 5 are predominantly urban residential areas and have foundations by clearing and affirmation. Areas 6 and 7 are vacant lots with a high load of clearing and garbage. Areas 8 and 9 are semi-industrial areas, with a greater predominance of urban transport bus companies (where buses are maintenenced and kept). Via 01 is the busiest route and shows the greatest amount of dumped garbage throughout the year. On the other hand, route 4 is an auxiliary road with less traffic; however, it is a route used to reach areas 6 and 7 that are used as a dump.

Sector B has only one area of possible influence, which is area 3 containing a school, a brewery and a church. In addition, this sector has track 3; an auxiliary route with little traffic.

Sector C is an area with possible influence of MP contamination towards the right bank, just 100 m from large industrial warehouses and factories. We included area 2 within the wetland since food wrappers were found at the viewpoint of the lagoon and on the sides. This area has route 1 with the same high-traffic and medium-traffic auxiliary route as route 2.

The water samples were taken starting from the bottom to the surface and for the sediment a minimum of 250 g was collected. The water samples were collected using a 25 µm Red Sparenet (The Environment Management’s CEO, Lima, Peru) with a diameter of 17 cm and a 250 mL glass collection vessel. The average volume filtered by the Sparenet net in each vertical trawl was 40 L (^{Su et al., 2019}). The sediment samples were collected with a Van Veen Dredge (The Environment Management’s CEO, Lima, Peru) with a sampling surface of 0.025 m² and a 600 mL collection vessel (^{Di and Wang, 2018}). During the collection of the water and sediment samples, there was no uniform depth in the area evaluated in the lagoon, and an average of 1.77 ± 0.47 m was obtained, with 1.33 m being the point of least depth.

MP extraction in water: The samples were placed in 150 mL 30 % H₂O₂ for two days due to the large amount of suspended plant matter in the water samples (^{Sruthy and Ramasamy, 2017}; ^{Edo et al., 2020}).

Extraction of MP in sediment: The samples were processed using the method of ^{Nuelle et al. (2014}) with some modifications. To increase the density of the water and separate the MP by density, 300 mL of a saturated solution of NaCl prepared with 380 g L^-1 (Willis method) was added and 100 mL from the surface, solids in suspension were manually separated (^{Edo et al., 2020}).

The MPs were fixed on 20-25 µm filter paper and placed inside Petri dishes of 60 mm in diameter, for analyzing the color, shape and size. The colors were separated into eight categories: blue, red, transparent, white, black, green, light blue/turquoise, and other colors (fuchsia, pink, gray, brown, and orange). The forms were separated into five categories: fragment, fiber, film, foam and pellet, while the sizes were classified into five levels: 50-100 µm, 101-200 µm, 201-300 µm, 301-400 µm and 401-500 µm (^{Zhang et al., 2017}; ^{Iannacone et al., 2019}; ^{Faria et al., 2021}). Units for MP in particulate water were expressed in L^-1 and in kg^-1 for MP in particulate sediment (Su et al., 2016; ^{Di and Wang, 2018}; ^{Edo et al., 2020}; ^{Huang et al., 2020}; ^{Zhou et al., 2020}).

The comparison of means of the MP values ​​in water and sediment among the sectors of the largest PVW lagoon was carried out with ANOVA and posteriori comparison with the Tukey test. Pearson correlation was perform between the amount of MP in water and sediment based on the sampling points. For all descriptive statistical calculations, the SPSS Statistics statistical package was used. For the shape, color and size of MP in water and sediment, tables based on their frequency were used. The level of significance was at an alpha of 0.05.

The total abundance of MP in the 16 water samples was 607 MP particles with a mean of 37.93 ± 16.87 MP particles·sample^-1 and 0.94 particles·L^-1. The total sum of MP in the 16 sediment samples was 162 MP with a mean 10.13 ± 3.68 MP particles·sample^-1 and 64 particles·kg^-1. The characterization of MP in water and sediment based on color and shape is described in Table 1 and the size is shown in Table 2.

Table 1 Shape and color of microplastics (MP) in water and sediment in the total samples from Laguna Mayor (PVW). 

Table 2 Ranges in size of the microplastics (MP) found in water and sediment samples from the Laguna Mayor (PVW). 

All the water and sediment sampling points presented MP (Figure 2). Differences were observed between MP (particles/sample) in water for sectors A (49.66 ± 15.57b), B (20.2 ± 4.81a) and C (41.61 ± 1.19b) (F = 8.86, P = 0.003). There were significant differences in sector B, which were well below the means of the other two sectors. Differences were noted between MP in sediment (particles/sample) for sectors A (13 ± 2.75b), B (6.4 ± 2.40a) and C (10.4 ± 2.40ab) (P = 0 .18, F = 9.19, P = 0.003).

Figure 2 Various shapes and colors of microplastics (MP) found in water and sediment from the Laguna Mayor (PVW). (A) MP blue fiber, (B) MP light blue film, (C) MP blue fragment, (D) turquoise fragment, (E) pink fiber, (F) transparent film, (G) blue fiber, (H) blue fragment, (I) yellow foam. 

The Laguna Mayor is subject to various sources of pollution, including urban and industrial anthropogenic activities, illegal destination of clearing, dumps and garbage disposal, as well as neighboring vehicular and pedestrian traffic (Su et al., 2016; ^{Di and Wang, 2018}; ^{Yuan et al., 2019}). The main cause of the accumulation of garbage, dry leaves, feathers and other light materials on the eastern edge of the Laguna Mayor is possibly due to drag by the direction of the wind. Indeed, sampling points from this side of the lagoon showed the highest amount of MP (P2, P5, P8, P11, P14 and P15) (^{Zhang et al., 2017}).

The first possible source of contamination is likely direct dumping of garbage by people into the lagoon or PVW perimeters, while the second possible source is air transport by the wind of plastic garbage with less mass such as styrofoam, bags or films. A third possible source is the transport of plastic waste ingested by birds or other representative PVW species and excreted in resting areas such as PVW, while the fourth possible source of contamination is the transport of plastic waste by birds to build nests. Finally, a likely fifth source is decomposition of the bodies of animals, such as fish, birds, rodents or small mammals, that had ingested plastics (^{Reynolds and Ryan, 2018}; ^{Blettler et al., 2020}).

In PVW, one of the possible sources of contamination of plastic garbage that can generate MP has been related to adjacent human activities, such as mechanical workshops, industrial warehouses, land with construction clearing, and garbage dumps, among others (^{Cepeda et al., 2019}). White MP (23 %) appeared in greater abundance. Several studies have demonstrated that zooplankton communities have a predisposition to ingest white MP because it resembles their prey (^{Iannacone and Alvariño, 2007}; Cepeda et al., 2019), while other studies have shown that the light blue/turquoise and blue colors of MP pose a greater threat to aquatic biota (^{Yuan et al., 2019}).

MP from water and sediment samples predominantly ranged from 401 to 500 um in size. MP less than 500 um in size have a longer retention time in the aquatic environment leading to greater accumulation in fish (^{Yuan et al., 2019}). Sector B of water samples presented less MP contamination than sectors A and C. Sector B was much more isolated by vegetation, which acted as a windbreaker, forming isolation areas and preventing the deposition of MP transported by the wind (^{Reynolds and Ryan, 2018}; ^{Carlin et al., 2020}).

In relation to sediment samples, sector B presented less contamination by MP (particles/sample) than sector A, but was similar to sector C. The transport of MP by air and the proximity to anthropogenic activities could be factors that explain the differences observed between sectors (Su et al., 2016; ^{Yuan et al., 2019}; ^{Zhou et al., 2020}).

In other studies of MP in continental waters, a greater amount of MP has been found in sediment. This may be due to three factors: the first is a greater amount of very dense MP, the second is the adhesion capacity of MP to join with other particles or form biofilm, causing its decline, and finally the third factor is environmental conditions such as temperature, wind, storms and internal waves (^{Di and Wang, 2018}; ^{Yuan et al., 2019}).

Fragment-type MPs predominated in both water (54.20 %) and sediment (51.85 %). These fragments are associated with shavings, drops or seams from the manufacture of plastics, especially as plastic material for packaging food and other products, as well as plastic bags (^{Bayo et al., 2019}).

In relation to the characterization of MP in water and sediment in the PVW in Chorrillos, in water there were 37.93 ± 16.87 particles of MP·sample^-1 and 0.94 particles·L^-1, and in sediment there were 10.13 ± 3.68 MP particles·sample^-1 and 64 particles·kg^-1. The predominant MP in water and sediment were white and light blue/turquoise color, with fragment and film forms, ranging from 401 to 500 um in size. There were differences between the MP in water and sediment when comparing the MP among the three PVW sectors. A correlation was observed between the abundance of MP in the water and sediment samples. Urban and industrial anthropic activities, illegal destination of clearings, dumps and garbage disposal, as well as vehicular and pedestrian traffic adjacent to the Laguna Mayor PVW, and the transport of MP by wind could be factors that explain the differences in MP in water and sediment from the different wetland sectors. Finally, further research is essential to evaluate the plastics and MP ingested by birds or other species in this wetland.