Ingestion and accumulation of microplastics in small marine fish and potential human exposure: case study of Binh Dinh, Vietnam

Abstract The present study investigates microplastic (MP) accumulation in five small marine fish species living in the nearshore sea of Binh Dinh, Vietnam that are commonly consumed by the local coastal communities. Fish (Oxyurichthys ophthalmonema, Stolephorus commersonnii, Decapterus macrosoma, Upeneus moluccensis, Sardinella gibbosa) were collected from four sites in the nearshore sea of Binh Dinh in rainy and dry seasons. The temporal, spatial, and species variations in MP accumulation were evaluated to understand environmental exposure of MPs to fish and potential human exposure to MPs via fish consumption. Microplastics of different types, sizes, and colors were found in the digestive system of the fish species. Microplastic composition included polyethylene, polyvinyl ether, polymethacrylate, polydichloroethylene, polydivinyl ester, poly ester, polyfluoroethylene, and other additives of plastic materials. Microplastic abundance in the fish was dependent on species, site, and season. Overall, microfiber was the dominant MPs. The average total MP abundance range was 4.70–23.80 particles/fish or 0.29–6.21 particles/g fish. There were statistically significant differences in MP abundances between fish species, sites, and seasons. The presence of MPs in the digestive system of fish suggests that MPs are in the nearshore environment of Binh Dinh. The local communities along the coast of Binh Dinh can ingest MPs from consuming small fish at a weekly rate equivalent to one five-hundredth number of rice grains they consume/week.


Introduction
Plastic production and use have been steadily increasing during the past two decades regardless of our concern about plastic pollution and impacts on the ecosystems and efforts to reduce plastic use.According to Plastic Europe, the world plastic production has increased from 200 million tons in 2000 to over 390 million tons in 2021 (Plastics Europe 2022).To the present time, most used plastic materials are directly or indirectly discarded into the environment at the end of their life cycle despite the human's efforts for reuse, recycling, and recovery of plastic materials (Wu et al. 2019;Hale et al. 2020).As a result, humanity is facing a global crisis of plastic pollution problem.The problem is more serious in developing countries where plastic consumption is increasing but waste processing facilities and environmental management are at a level that needs more development and improvement to tackle the pollution problem.Vietnam has been believed to be among the five countries in the world that release most plastic waste into the ocean.This can contaminate the coastal environment of Vietnam and contribute to plastic pollution in the ocean.
Once entering the environment, large plastic materials can be broken into small pieces via chemical and biochemical degradations causing by photochemical and biochemical reactions and physical and mechanical fragmentations causing by wave forces and collisions with other environmental objects (e.g., rock, soil, plant litter) (Andrady 2011;Weinstein et al. 2016;Wu et al. 2019;Li et al. 2020).Plastic particles with sizes of 1 mm-5 mm are considered microplastics (MPs) (Alimi et al. 2018).Nanoplastics (NPs) are plastic particles with sizes less than 1 mm (Alimi et al. 2018).Microplastics and NPs coming from the natural degradation and fragmentation processes are called secondary plastic particles.Primary MPs and NPs are synthetic plastic particles used in industrial and commercial products, such as plastic microbeads used in cosmetic products, hand soaps, cleaning agents, coatings and paints, drilling fluids in oil and gas industry, and precursor resins and pellets for manufacturing finished plastic products (Hale et al. 2020).In addition, synthetic fibers from commercial and household laundries and plastic product making plants and recycling facilities are important primary MP and NP sources for the environment (Kay et al. 2018;Wu et al. 2019;Li et al. 2020;Tran et al. 2023).The problems of primary MPs and NPs sources can be more profound in developing countries, where industrial and residential waste waters are usually released into the environment without treatment.
Plastics are persistent in the natural environment.They can last for hundreds of years and be transported with waterflow in freshwater ecosystems and the ocean current in marine ecosystems.Microplastics and NPs are ingested by living organisms and transferred through the food chain and food web, especially in the aquatic ecosystem (Canniff and Hoang 2018;Guzzetti et al. 2018;Wu et al. 2019;D'Souza et al. 2020;Hoang and Felix-Kim 2020;Hoang and Mitten 2022).More than 150 fish species in the natural environment have been widely reported to ingest MPs in different amounts (Su et al. 2019) including fish for human consumption (Daniel et al. 2020).The ingestion of MPs by marine organisms has been reported to increase by 2.4% during the last decade (Savoca et al. 2021).The transfer of MPs and NPs through the food chain and food web enhances and further spreads their transport and fate in the ecosystem and increases exposure potential and effects to biota, including humans (Sharma and Chatterjee 2017;Hoang and Mitten 2022;Makhdoumi et al. 2023).
To assess risks and effects of MPs and NPs on biota, measurement of MP and NP ingestion and accumulation in living organisms is necessary.Ingestion and accumulation of MPs and NPs in organisms are dependent on the particle abundance in the environment and their shape and relative size to the size of organisms (Akhbarizadeh et al. 2018;Makhdoumi et al. 2023).Therefore, the accumulation is expected to be varied temporally and spatially, depending on the sources of MPs and NPs to the receiving environment (Canniff and Hoang 2018;Wu et al. 2019;Hoang and Felix-Kim 2020;Hoang and Mitten 2022).In addition, feeding and living habitat of organisms also determine potential direct ingestion of plastic particles from water or through the trophic chain (Akhbarizadeh et al. 2018).The coastal environment of Vietnam has been reported to have MPs at abundances that are within MP abundances in marine environments worldwide (Lahens et al. 2018;Wu et al. 2019;Strady et al. 2021).Several studies have reported MPs accumulation in bivalves (Nam et al. 2019;Hue et al. 2021;Do et al. 2022;Tran-Nguyen et al. 2023;My et al. 2023a) and shrimp (My et al. 2023b) in Vietnam.Most studies on MP accumulation in organisms in Vietnam were conducted with organisms living along the shoreline.However, MP and NP ingestion and accumulation in marine fish in Vietnam have not been reported.Lacking information on MP and NP accumulation in fish will limit our ability to conduct ecological and human health risk assessments for MPs and NPs because seafood is one of the main protein sources for the Vietnamese, especially for the local communities along the coast of Vietnam.The present study investigates MP accumulation in five small marine fish species living in the nearshore sea of the Province of Binh Dinh, Vietnam that are commonly consumed by the local communities.The temporal, spatial, and species variations in MP accumulation were evaluated to understand environmental exposure of MPs to fish and potential human exposure to MPs via fish consumption, especially for the local communities in the coast of Binh Dinh that mostly consume fish they catch from the ocean.

Sampling
To achieve the study objectives, five common small saltwater fish species belonging to five family groups were chosen for measuring MP accumulation in their digestive system.The species were Oxyurichthys ophthalmonema (Goby), Stolephorus commersonnii (Anchovy) Decapterus macrosoma (Pompano), Upeneus moluccensis (Goatfish), and Sardinella gibbosa (Hering) (see their pictures in Figure S1).These fish species can be found in water within 10 km out from the shoreline.Oxyurichthys ophthalmonema and U. moluccensis are demersal fish.The other three species are pelagic fish.The fish are small and usually consumed as a whole body by the local communities.Therefore, MPs in their digestive system can be transferred to humans when they are consumed.To determine spatial difference in MP accumulation in fish, fish were caught by local fisherman from four sites in the nearshore sea of Thi Nai Lagoon (Site 1), De Gi of Phu Cat District (Site 2), Xuan Thanh of Phu My District (Site 3), and Tam Quan (Site 4) (Figure 1).These land sites are approximately 25-30 km apart north to south.Fish were caught approximately 2 km southeast from the shoreline of Thi Nai Lagoon.For De Gi, Xuan Thanh, and Tam Quan sites, fish were caught at approximately 6, 3, and 4 km east out from the shoreline, respectively.Sampling was conducted in the rainy season (December 5-24, 2020) and dry season (March 20-29, 2021) that allows comparison of temporal differences in MP accumulation in fish (see Table S1 for the detailed sampling date of each site).Three fish species per site were designed for the study.However, fish sampling was based on fish availability for each site and season.Among the five species, S. commersonnii was the only species that was available at the four sites in both seasons.Three fish species for Site 1 were O. ophthalmonema, S. commersonnii, and S. gibbosa.For Site 2, the fish species were S. commersonnii, D. macrosoma, and U. moluccensis.Site 3 and Site 4 species were O. ophthalmonema, S. commersonnii, and D. macrosoma.Fish were sampled when the fisherman returned to the beach from the fishing sites.On the beach, ten individual fish of each species were randomly selected, purchased, placed in a plastic zip bag (one bag/species), and kept in a cooler with ice for transporting to the biology laboratory of Quy Nhon University for analysis.In the laboratory, fish were frozen in a freezer at −10 � C until analysis.A total of 240 fish representing 240 samples were purchased for the study (3 fish species/site/season � 10 individuals/fish species � 4 sites � 2 seasons).
To estimate MP ingestion by the local communities from fish consumption, a survey was conducted to assess their fish consumption.The survey was conducted with ten participants in Hoai Nhon Town (Tam Quan site) that represents the study sites, and in Tuy Phuoc District, a district bordering Thi Nai Lagoon, at which the local communities usually purchase fish caught from Thi Nai Lagoon for consumption.The participants were chosen to equally represent gender, occupation, and site as much as possible.Five males and five females and five participants in each district were asked questions to obtain information for their fish consumption amount per week.Detailed questions of the survey can be seen in the supplemental information (Table S2).The survey information was used to estimate the average amount of fish consumed per person per week for each fish species.The number of MP particles ingested per person per week was calculated by multiplying the MP abundance by fish weight with the amount of fish consumed per person per week (Table S3).

Analysis of microplastics
To prepare samples for MP analysis, each individual fish was first thawed under the laboratory temperature of 25 ± 1 � C, rinsed carefully with deionized water (DI) three times to remove dirt and potential MPs on the fish body, and weighed on a Shimadzu Analytical Balance BL-620S with the readability of 0.01 g to determine the wet weight of the fish.After measuring the fish weight, the total fish length (from the tip of the mouth to the tip of the tail) was measured with a regular ruler to the nearest mm (Figure S1) on a tempered glass cutting board.Fish were then rinsed carefully with DI water three times to remove potential MP contamination during measuring weight and length and dissected on the tempered glass cutting board for the digestive system (stomach and intestine) using a standard dissection test kit.The tempered glass cutting board was also washed carefully with ID water to remove potential MP contamination during measuring weight and length before use for dissection.The digestive system was transferred to a glass beaker that has been acid and acetone washed, dried, and covered with aluminum foil to prevent airborne MP deposition.The sample was digested with 10% KOH at 60 � C following the most common procedures for MP analysis published by Masura et al. (2015).However, density separation was not applied for the sample because it did not contain sediment.The digestion was conducted for 3-5 days, depending on fish species and the sample size, until the digestive system was totally digested.The solution was filtered with Whatman glass fiber filters with the pore size of 1 mm.The filters were dried at laboratory temperature of 25 ± 1 � C for approximately six hours and kept in a glass petri dish with cover until analysis of MPs at Quy Nhon University.A Leica Stereomicroscope S9i was used to look for and count MPs on the filters.The microscope was equipped with a high-resolution camera and LASX software that allowed measurement of particle size (length for fibers, area for fragments).Microplastic color was also recorded.The analysis was conducted on individual fish.The composition analysis of plastic particles was conducted using a Jasco Fourier Transform Infrared Spectroscopy (FTIR, 6800) in Dr. Yaniv Olshansky's laboratory at Auburn University, Alabama, USA.A subset of 43 samples with large size MPs (18% of the total samples) that would be grabbed by a forceps was analyzed using reflection mode.Microplastics were transferred from filters to the FTIR for analysis.A blank sample was included in each set of samples for digestion and serves as a QC sample for the digestion process.A blank filter was also set on the lab station during counting and measuring MPs under microscope.This blank filter serves as a QC sample for MP measurement.A total of 30 QC samples were included throughout the course of the study.In addition, to minimize and prevent potential MP contamination during preparing samples, the surface of the lab station was wiped using Kim wipe papers wetted with DI water before use.The lab floor was swept before preparing samples.A cotton lab coat was worn during sample preparation and measurement.The samples were covered with aluminum foil during digestion to prevent airborne MP deposition.

Data analysis
Microplastic abundance was calculated and expressed in number particles/fish and number particles/g fish.The latter measurement unit was calculated by dividing the number of particles by the fish weight.The abundance data were used for comparison for statistically significant differences between fish species, seasons, and sites.The comparison was conducted using the student t-Test method by Minitab 19.Square root, inversion, and log transformation methods were used to transform the data that did not meet the assumption of homogenous variance and normal distribution for the comparison.Relative abundance of MPs by size, type, and color was also calculated.Pearson Correlation analysis was conducted to determine the correlations between MP abundance with fish length and fish weight.

Fish length and weight
The total length and weight of fish samples in the present study varied by species, site, and season.The average total fish length by site and season of the five species ranged from 5.48 to 8.89; 4.52 to 9.50; 10.39 to 11.85; 6.89 to 12.50; and 5.93 to 6.12 cm for O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis, respectively (Table 1).Their respective average weight ranges were 3. 78-12.32, 3.52-9.31, 20.97-27.18, 4.80-26.05, and 3.18-3.46g (Table 1).No statistical comparison for significant difference in length and weight was conducted because they were wild caught.Their age, life stage, and sex that influence the fish size were unknown.Overall, U. moluccensis appeared to have the smallest weight among the fish samples.D. macrosoma had the largest weight.The total length of S. gibbosa was the longest.The overall population of U. moluccensis appeared to have the shortest total length, although the shortest total length of 3.50 cm was measured for an individual S. commersonnii from Site 3 in dry season.According to the length and weight data reported by El-Betar and Osman (2021), Tampubolon et al. (2021), andNair et al. (2021), the population of S. gibbosa and S. commersonnii sampled in the present study would have reached at least the first maturity stage.The total length recorded for D. macrosoma and U. moluccensis in the present study was below their matured length reported by Widodo (1988), Syahailatua (2004), andIsmen (2005).Therefore, D. macrosoma and U. moluccensis in the present study would be younger than the maturity stage.No egg was observed when dissecting fish for their digestive system.This suggests that the fish likely have not reached reproductive stage, including O. ophthalmonema.

Microplastic accumulation in fish
Microplastics with different types (fiber, film, fragment), sizes (length, area), and colors (clear/white, blue, black, brown, green, purple, pink, orange, red, gold) were found in the digestive system of all individuals of the five fish species in the present study (Figure 2).Among 30 QC samples, two samples had two MPs.For fish samples, at least one MP was found in an individual digestive system.The fish that accumulated the most MPs was S. gibbosa from Thi Nai Lagoon (Site 1) and in the rainy season (49 MPs, Table 1).Plastic composition analysis was conducted for large size MPs.Two out of 43 samples analyzed did not appear to contain chemical components of plastic materials.The composition of the other 41 samples were polymers and chemical components ) § MPs (total # particles/fish) MPs (# particles/g fish, ww) of plastic materials, such as polyethylene, polyvinyl ether, polymethacrylate, polydichloroethylene, polydivinyl ester, poly ester, polyfluoroethylene, and other additive components of plastic materials (e.g., such as plasticizers) (Table S1).
Microplastics were classified into two categories: fiber and fragment (fragment and film).The fiber length varied largely.The shortest fiber with a length of 92 mm was found in the digestive system of O. ophthalmonema collected from Thi Nai Lagoon (Site 1) in the rainy season (Table 1).The longest fiber with a length of 10,888 mm was detected in the digestive system of U. moluccensis from De Gi Sea (Site 2) in the dry season (Table 1).The average fiber length by site and season ranged from 1,220 to 2,164, 1,358 to 1,945, 1,245 to 1,521, 986 to 1,900, and 1,549 to 1,569 mm for O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis, respectively (Table 1).The smallest fragment had an area of 800 mm 2 , which was detected in the digestive system of S. commersonnii from Thi Nai Lagoon (Site 1) in the rainy season ((Table 1).D. macrosoma from De Gi Sea (Site 2) in the dry season accumulated the largest fragment with an area of 3,734,275 mm 2 (Table 1).The average area of fragments ranged from 83,888 to 353,484, 114,164 to 452,368, 51,676 to 178,113, 120,581 to 615,034, and 142,781 to 184,260 mm 2 for O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis, respectively (Table 1).
The lowest and highest average total MP abundances by individuals were found in D. macrosoma from De Gi Sea (Site 2) in the dry season (4.70 particles/fish, Table 1) and Xuan Thanh Sea in the dry season (23.80 particles/fish, Table 1), respectively.The average total MP abundance (by individuals) by site and season in O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis ranged from 6.20 to 17.20, 9.70 to 20.30, 11.60 to 11.60, 4.70 to 23.80, and 12.10 to 14.30 particles/fish, respectively (Table 1).These MP abundance data were based on MP counts by microscope.The lowest and highest average total MP abundances by fish weight were found in D. macrosoma from De Gi Sea (Site 2) (0.29 particles/g fish) and in S. commersonnii from Xuan Thanh Sea (Site 3) in the dry season (6.21 particles/g fish), respectively (Table 1).The average total MP abundance (by fish) by site and season weight for O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis ranged from 1.30 to 3.20, 1.09 to 6.21, 0.44 to 0.59, 0.29 to 5.16, and 4.12 to 4.35 particles/g fish, respectively (Table 1).
Comparison of MP accumulation between fish species and seasons showed statistically significant differences for some species between sites and seasons.For Thi Nai Lagoon (Site 1), there was no statistically significant difference in the average total MP abundance by individuals.However, the average total MP abundance by fish weight for S. gibbosa in the dry season was statistically significantly lower than the abundances by fish weight for O. ophthalmonema and S. commersonnii in the same season (Figure 4A).For De Gi Sea (Site 2), the average total MP abundance by individuals for D. macrosoma in the dry season was statistically significantly lower than the abundances by fish weight for S. commersonnii and U. moluccensis in the same season.There was also a statistically significant difference in the average total MP abundance by individuals for D. macrosoma between the rainy and dry seasons (Figure 4B).The average total MP abundance by fish weight for U. moluccensis in the rainy season was statistically significantly higher than the abundances by fish weight for D. macrosoma and S. commersonnii in the same season (Figure 4B).For the dry season, the average total MP abundances by fish weight for the three fish species were statistically significantly different.There was a statistically significant difference in the average total MP abundance by fish weight for D. macrosoma between the two seasons (Figure 4B).For Xuan Thanh Sea (Site 3) and within a season, the average total MP abundances by individuals for three fish species were not statistically significantly different.However, the abundances by individuals were statistically significantly different between the two seasons for S. commersonnii and D. macrosoma (Figure 4C).The average total MP abundance by fish weight for O. ophthalmonema in the rainy season was statistically significantly higher than the abundances by fish weight for S. commersonnii and D. macrosoma.There was a statistically significant difference in the abundance by fish weight between the two seasons for S. commersonnii and D. macrosoma (Figure 4C).With Tam Quan Sea (Site 4), the average total MP abundance by individuals for O. ophthalmonema in the rainy season was statistically significantly lower than the MP abundances by individuals for S. commersonnii and D. macrosoma (Figure 4D).There was no seasonal difference in MP abundance by individuals for each fish species.The average total MP abundances by fish weight for three fish species in the rainy season were statistically significantly different from each other (Figure 4D).For the dry season, the average total MP abundance by fish weight for D. macrosoma was statistically significantly lower than the abundances by fish weight for O. ophthalmonema and S. commersonnii.There was a statistically significant seasonal difference in MP abundances by fish weight for S. commersonnii (Figure 4D).
Comparison of MP accumulation in the same species from different sites showed that the accumulation was site dependent.The average total MP abundance by individuals for O. ophthalmonema from Tam Quan Sea in the rainy season was statistically significantly lower than the abundances by individuals for O. ophthalmonema from Xuan Thanh Sea and Thi Nai Lagoon in the same season (Figure 5A).However, the average total MP abundance by fish weight for O. ophthalmonema from Xuan Thanh Sea in both seasons were statistically significantly higher than the MP abundances by fish weight for O. ophthalmonema from Tam Quan Sea and Thi Nai Lagoon (Figure 5A).With S. commersonnii, only average total MP abundance by individuals for fish from Xuan Thanh Sea in the dry season was statistically significantly higher than the abundances by individuals for fish from other three sites in the same season (Figure 5A).A similar difference in MP abundance by fish weight between the four sites was found for S. commersonnii in the dry season (Figure 5B).In addition, the average total MP abundances by fish weight for S. commersonnii from Tam Quan Sea and Thi Nai Lagoon were statistically significantly higher than the MP abundances by fish weight for fish from Xuan Thanh Sea and De Gi Sea in the rainy season (Figure 5B).For D. macrosoma, the average total MP abundances by fish weight for fish from Tam Quan Sea, Xuan Thanh Sea, and De Gi Sea in the dry season were statistically significantly different (Figure 5C).The average total MP abundances by fish weight for fish from the three sites in the rainy season were statistically significantly different (Figure 5C).For the dry season, the MP abundance by fish weight for fish from Xuan Thanh Sea was statistically significantly higher than the MP abundance by fish weight for fish from the other two sites (Figure 5C).
The results of correlation analysis showed that except for D. macrosoma it displayed some levels of weak correlations, the MP abundance by individuals was negatively weakly correlated with fish length and fish weight when the correlation analysis was conducted for each species separately or all species together (Table 2).However, the MP abundance by fish weight appeared to have a negative weak (i.e., O. ophthalmonema, S. gibbosa) to strong correlation (i.e., S. commersonnii, D. macrosoma, all fish) with fish length and fish weight.These results indicate that MP abundance by individuals for the five fish species is not dependent on the fish length and fish weight, but the abundance by fish weight would decrease when fish length and fish weight increase.Fish length and fish weight were strongly correlated.

Fish consumption and microplastic ingestion by the local communities
The survey showed that on average each person regardless of gender consumed one of the five species at the amount of 125.00, 145.83, 208.33, 91.67, and 100.00 g fish/week for O. ophthalmonema, S. commersonnii, S. gibbosa, D. macrosoma, and U. moluccensis, respectively (Table 3).The respective MP ingestion per person from consumption of these fish species was 308.54, 337.97, 107. 29, 140.40, and 423.50 particles/week or 16,044.17, 17,574.38, 5,579.17, 7,300.94, and 22,022.00particles/year (Table 3).On average, the weekly and yearly MP ingestions were 263.54 and 13,704 particles, respectively (Table 3).

Environmental contamination, exposure, and risk of microplastics to marine organisms
The MP abundances found in the digestive system of the five fish species in the present study varied largely and were dependent on species, study site, and season.The MP abundances in fish ranged from 1 to 49 particles/fish or 0.05 to 11.94 particles/g fish.The species average MP abundances ranged from 4.70 to 23.8 particles/fish or 0.29 to 6.21 particles/g fish.These MP abundances are within the abundances in the digestive tract of marine fish published by previous research.For example, Abadi et al. (2021) reported an abundance of 11.4 MPs/individual for Rutilus Frisii.Feng et al. (2019) found abundances of 3.00-6.32MPs/individual in the gut of six fish species or 1.61-11.19MPs/g fish (Thryssa kammalensis, Amblychaeturichthys hexanema, Odontamblyopus rubicundus, Cynoglossus semilaevis, Chaeturichthys stigmatias and Collichthys lucidus).According to Zakeri et al. (2020), the digestive system of Chelon aurata and Rutilus kutum accumulated MPs at an abundance of 2.95 MPs/fish.The MP abundances found in the present studies are also within the MP abundances reported for non-fish species in Vietnam.My et al. (2023a) found an average MP abundance range of 2.5-8.6 MPs/individual or 0.5-1.1 MPs/ g farmed or wild caught shrimps (greasy-back shrimp (Metapenaeus ensis), green tiger  � Data for each species were the site and season average of MP abundances for each species reported in Table 1.
shrimp (Penaeus semisulcatus), white-leg shrimp (Litopenaeus vannamei), giant tiger shrimp (Penaeus monodon)).Another study by Do et al. (2022) detected MPs in framed oysters in Vietnam at an abundance of 18.55 MPs/individual or 1.88 MPs/g oyster (Crassostrea gigas).However, lower MP abundances in the digestive system of marine fish have been reported in the literature.According to Pereira et al. (2020), the average MP abundances in the stomach of six fish species including blue Jack mackerel (Trachurus picturatus), chub mackerel (Scomber japonicus), skipjack tuna (Katsuwonus pelamis), blackbelly rosefish (Helicolenus dactylopterus), and blackspot seabream (Pagellus bogaraveo) ranged from 0.04 to 0.22 MPs/fish.Another study by Klangnurak and Chunniyom (2020) found MPs in the digestive tract of 15 marine fish species in the Gulf of Thailand and Andaman Sea at an abundance range of 0.03-0.4MPs/fish.Similarly, Koongolla et al. (2020) found MPs in 12 out 24 marine fish species in Beibu Gulf, South China Sea at an abundance range of 0.027-1.000MPs/fish.Their later study with other 32 marine fish species in Beibu Gulf found an average MP abundance of 1.02 MPs/fish (Koongolla et al. 2022).Previous research with non-fish species in Vietnam also found lower MP abundances.For example, Hue et al. (2021)  Vietnam detected MPs at abundances ranging from 1 to 9 MPs/individual or 0.1 to 1.0 MPs/g organisms (My et al. 2023b).The literature MP abundances of aquatic organisms are up to several fold lower than the abundances found in the present study.The differences in MP accumulation found in the present study and reported in the literature would be due to different factors, such as the level of environmental contamination, species of organisms which is related to their feeding habitat, organism size, life stage, sex, and ability to excrete MPs after ingestion.However, information for these influencing factors was not reported with the MP accumulations.Microplastic accumulation in the five fish species investigated in the present study have not been studied.Although MP accumulation in marine fish is largely different between species, the relative distribution of MP types is similar regardless of fish species and study site.The dominant plastic particle type was microfibers.The percentage of microfibers found in the present study ranged from 56 to 74% (average of 69%) (Figure 3C).Koongolla et al. (2020Koongolla et al. ( , 2022) ) found 96% and mostly > 80% microfibers in their fish samples, respectively.Another study by Klangnurak and Chunniyom (2020) found that microfibers accounted for 57 to 83% in the samples analyzed.Most MPs found by Feng et al. (2019) and Huang et al. (2020) were microfibers (> 60% and 98%, respectively).The dominant microfibers found in fish can be explained by the dominance of microfibers in the aquatic environment.It also reflects a contaminant exposure-accumulation relationship.
For microfiber length distribution, the dominant length found in the present study was from greater than 1,000 to 5,000 mm (55-64%) (Figure 3A).Microfibers at length of 100-1,000 mm accounted for 34 to 44%.Fibers with lengths less than 100 mm or greater than 5,000 mm were less than 3%.These results indicate that most plastic particles found in the digestive system of the five fish species in the present study are microplastics.The microfiber length distribution in the present study is similar to that reported by Huang et al. (2020).However, the microfiber length distribution is different from that of Koongolla et al. (2020Koongolla et al. ( , 2022)), who reported a dominant microfiber length range of 20-1,000 mm.Feng et al. (2019) found most microfibers at lengths of less than 1,000 mm.These comparisons suggest that fish in the present study would ingest longer microfibers than fish in the studies by Koongolla et al. (2020Koongolla et al. ( , 2022) ) and Feng et al. (2019).
Among the colors of MPs found in the present study, white/clear, gold, and blue occurred more frequently than other colors and accounted for 16-49%, 27-41%, 12-23%, and respectively (Figure 3D).It is important to mention that for certain colors, such as pink versus purple, orange versus gold and light yellow, and white versus clear and transparent, the recognition can be influenced by the lighting condition of microscope, resolution of camera, and direct observation from the microscope eyepiece or observation from the computer monitor.The colors can be easily misrecognized.Therefore, caution should be taken when comparing these colors of MPs, especially between studies by different researchers.Nevertheless, the color distribution of MPs found in the present study appears to be similar to the color distribution of MPs reported by Huang et al. (2020) with the consideration of orange and gold colors in the present study similar to brown and yellow colors in Huang et al. (2020).However, the color distribution reported by Koongolla et al. (2020Koongolla et al. ( , 2022) ) are different.The dominant color in Koongolla et al. (2020) was transparent (83%).Red, blue, and green colors accounted for 17%.Koongolla et al. (2022) observed more black, blue, and red MPs but less white and transparent MPs.The color distribution reported by Klangnurak and Chunniyom (2020) seems to be more similarly distributed among red (29-31%), blue/blue light (14-24%) and transparent (21-29%).Aquatic organisms can have color and species preference for prey items.The question of whether the different colors of MPs found in the digestive system of fish would reflect their color preference for prey items is still unanswered.More laboratory research with MP color control should be conducted to answer this question.
The present study found MPs of different types, sizes, and abundances in five fish species living in the nearshore marine areas of the Province of Binh Dinh.The presence of MPs in the digestive system of fish suggests that the environment where they live must have MPs.This suggestion can be supported by Strady et al. (2021) who reported MP contamination with high abundances of microfibers in freshwater and marine environments of Vietnam, including Thi Nai Lagoon.The microplastic abundances in fish found in the present study are site, season, and species dependent.Overall, the abundances for fish sampled from Xuan Thanh Sea in the dry season were higher than those for fish from other sites (Figures 4C and 5).These results suggest that MPs in the nearshore marine area of Xuan Thanh Sea, where the fish were caught from, would have more MPs than other the nearshore marine areas of Binh Dinh.The results also suggest that the nearshore marine environment of Xuan Thanh Sea would have more MPs in the dry season than the rainy season.Microplastic contamination in nearshore marine environments can be more influenced by local sources than ocean current driving sources and atmospheric fallout.Results of the present study signify potential local MP sources to the nearshore environment of Xuan Thanh Sea of Binh Dinh.Although the detailed sources are unknown, there are several large garment factories (i.e., Vinatex, Oasis) and numerous smaller clothing manufacturers in Phu My District (e.g., Quang Hiep, Phuc Hung, Huy Hoang, Binh Duong, Tuan Vinh).Fibers can be released into the environment from the garment industry if waste and exhaust air are not properly managed.
The results of the present study indicate that the nearshore marine ecosystem of the Province of Binh Dinh is contaminated with MPs.Aquatic organisms in addition to the five fish species researched in the present study are at risk of MP exposure.The question of whether MP contamination could affect aquatic organisms is still unanswered.Monitoring of MPs in the inland and nearshore environments in these coastal areas of Binh Dinh should be conducted to determine potential local MP sources.Research including control fish should be conducted to understand potential effects of MP exposure in the nearshore ecosystem of Binh Dinh.

Potential human exposure and ingestion of microplastics from fish consumption
The local community in Vietnam, especially for the fishermen communities along the coast of Vietnam usually consume fish they catch from the ocean for protein source.Although the living conditions nowadays have been significantly improved, their traditional eating habit of seafood remains.They usually eat small fish as a whole body.As a result, they can be exposed to MPs in the fish.Results of the survey showed that consuming small fish like the five species in the present study can result in an MP ingestion rate of 107.29-223.50particles/person/week or 55,79.17-22.022particles/person/ year, depending on fish species.This yearly ingestion of MPs from consumption of small fish can be equivalent to up to one five-hundredth the number of rice grains, the main carbohydrate source, the Vietnamese people consume per week (4.23 kg rice/person/week � 30,000 grains/kg ¼ 126,923 grains/person/week, Helgi Library 2023; Kitsunerestaurant 2023).These are conservative estimations and did not include MPs with sizes of less than 92 mm and MPs that might have accumulated in other parts of the fish body.The accumulation of MPs in gills, blood stream, liver, muscles, and on fish body have been reported in the literature (Abbasi et al. 2018;Feng et al. 2019;Huang et al. 2020;Koongolla et al. 2020Koongolla et al. , 2022;;Savoca et al. 2021;Ugwu et al. 2021).In addition, the eating habits of the local coastal communities in Vietnam would lead to more MP exposure and ingestion.They, in fact at some levels, prefer to eat smaller fish, especially for S. commersonnii.Other aspects of these conservative estimations are that some non-plastic particles as confirmed by the composition analysis and less than 3% of fibers that were longer than 5,000 mm were included in the estimations, while fibers of greater than 5,000 mm are not considered microplastics by the common definition.The concept and definition of microplastics by size have been controversially discussed (Hoang 2022).Fibers with lengths greater than 5 mm can be considered microplastics, but fragments with dimensions of greater than 5 mm or round estimated areas of greater than 25 mm 2 are likely too big to be considered microparticles.Zooplankton are unable to ingest these large plastic fragments but can ingest plastic fibers of 5 mm or some longer as fibers can fold and twist.Research has found twisted microfibers in the digestive system of Daphnia magna (Jemec et al. 2016).Microplastic abundance by individuals was weakly correlated with the fish length and fish weight, while the abundance by fish weight had a stronger negative correlation with the fish length and weight.These results of correlation analysis suggest that consuming more smaller individual fish would get more MP exposure and ingestion than consuming fewer larger individual fish at the same total consumption amount.
According to Mohamed Nor et al. (2021), the median MP intake rates for children and adults are estimated at 553 or 883 particles/person/day, respectively.Based on these estimated daily MP intake rates, the weekly MP intake rates would be 3,871 and 6,181 particles/person.These weekly intake rates are about 14 and 23 times higher than the average weekly intake rate estimated from consumption of small fish alone in the present study.All exposure routes including inhalation, drinking, and diet were taken into consideration for estimating the MP intake rate by Mohamed Nor et al. (2021), while the estimations in the present study were based on consumption of small fish only.More research should be conducted to better assess MP exposure, ingestion, and potential health impact on the local fisherman communities in the coast of the Province of Binh Dinh.

Conclusions
The present study found MPs of different types, sizes, and abundances in the digestive system of all individuals of five small marine fish species from the offshore sea of the province of Binh Dinh that are commonly consumed by the local fisherman communities.The MP abundances were dependent on fish species, site of collection, and season.Among the fish analyzed, fish sampled from the offshore sea of Xuan Thanh had the highest MP abundance.The presence of MPs in the digestive system of fish suggests that the offshore sea of Binh Dinh where fish were sampled from must have MPs.The results also signify potential local MP sources to the offshore sea of Xuan Thanh.Marine organisms other than the five fish species in the present study would be at risk of MP exposure.The local fisherman communities along the coast of Binh Dinh can be exposed to MPs from consumption of MP contaminated fish.More research should be conducted to determine potential local sources of MPs to the inland environment and nearshore and offshore seas of Binh Dinh and to evaluate potential health risks of MP exposure to the local fisherman communities of the Province of Binh Dinh.

Figure 2 .
Figure 2. Microplastics in the digestive system of fish collected from the nearshore sea of the Province of Binh Dinh, Vietnam in December 2020 and March 2021 (A: O. ophthalmonema; B: S. commersonnii; C: U. moluccensis; D: D. macrosoma; E: S. gibbosa).

Figure 4 .
Figure 4. Comparison of microplastic accumulation between fish species and seasons (A: Thi Nai Lagoon; B: De Ghi Sea; C: Xuan Thanh Sea; D: Tam Quan Sea; Error bars represent standard deviations of the means; data for the same season with different label letters are significantly different; asterisks represent significantly different accumulations between two seasons).

Figure 5 .
Figure 5.Comparison of microplastic accumulation in fish at different sites (A: O. ophthalmonema; B: S. commersonnii; C: D. macrosoma; Error bars represent standard deviations of the means; data for the same season with different label letters are significantly different).

Table 1 .
Fish length and weight and microplastic accumulation. 2

Table 2 .
Correlation between microplastic abundance, fish length, and fish weight.

Table 3 .
Microplastic ingestion by humans from fish consumption.