Assessment of macro-, meso- and microplastics in wild and cultivated Perna perna mussels (Mollusca: Bivalvia)

Introduction

When improperly discarded or released into the environment, solid waste can travel great distances, contaminating various ecosystems, spreading invasive species, creating socioeconomic challenges, harming human health and negatively affecting tourism (Hirata et al. 2017Hirata G., Viana E., Filho H.F., et al. 2017. Caracterização de pellets plásticos na Praia do Tombo, município do Guarujá, SP, Brasil. Rev. Int. Cienc 7(2): 202-216. https://doi.org/10.12957/ric.2017.29271
, Olivatto et al. 2018Olivatto G.P., Carreira R., Tornisielo V.L., et al. 2018. Microplásticos: Contaminantes de preocupação global no Antropoceno. Rev. Virtual Quím. 10. https://doi.org/10.21577/1984-6835.20180125
, Silva et al. 2018Silva M.L., Castro R.O., Sales A.S., et al. 2018. Marine debris on beaches of Arraial do Cabo, RJ, Brazil: an important coastal tourist destination. Mar. Pollut. Bull. 130: 153-158. https://doi.org/10.1016/j.marpolbul.2018.03.026
, Machado et al. 2021Machado J.Á., Oliveira S., Nazário M.G., et al. 2021. Análise da presença de microplástico em bivalves (Perna perna): um estudo de caso em Matinhos, litoral do Paraná. Rev. Bras. Des. Territ. Sust 7(1). https://doi.org/10.5380/guaju.v7i1.76916
). Research has consistently shown that plastic is the most prevalent type of waste on beaches and coastal areas (Silva et al. 2018Silva M.L., Castro R.O., Sales A.S., et al. 2018. Marine debris on beaches of Arraial do Cabo, RJ, Brazil: an important coastal tourist destination. Mar. Pollut. Bull. 130: 153-158. https://doi.org/10.1016/j.marpolbul.2018.03.026
, Olivatto et al. 2019Olivatto G.P., Martins M.C.T., Montagner C.C., et al. 2019. Microplastic contamination in surface waters in Guanabara Bay, Rio de Janeiro, Brazil. Mar. Pollut. Bull. 139: 157-162. https://doi.org/10.1016/j.marpolbul.2018.12.042
, da Silva et al. 2022Da Silva E.F., Carmo D.F., Muniz M.C., et al. 2022. Evaluation of microplastic and marine debris on the beaches of Niteroi Oceanic Region, Rio De Janeiro, Brazil. Mar. Pollut. Bull 175: 113161. https://doi.org/10.1016/j.marpolbul.2021.113161
). This is largely due to plastic’s durability, resistance and low cost, which have made it integral across numerous sectors such as single-use products, food packaging, cosmetics (e.g. scrubs and abrasives), medical equipment, construction materials and textiles, effectively replacing traditional materials in these industries (Dehaut et al. 2018Dehaut A., Hermabessiere L., Duflos G., 2018. Current frontiers and recommendations for the study of microplastics in seafood. Trends Anal. Chem 116: 346-359. https://doi.org/10.1016/j.trac.2018.11.011
, Olivatto et al. 2018Olivatto G.P., Carreira R., Tornisielo V.L., et al. 2018. Microplásticos: Contaminantes de preocupação global no Antropoceno. Rev. Virtual Quím. 10. https://doi.org/10.21577/1984-6835.20180125
, Machado et al. 2021Machado J.Á., Oliveira S., Nazário M.G., et al. 2021. Análise da presença de microplástico em bivalves (Perna perna): um estudo de caso em Matinhos, litoral do Paraná. Rev. Bras. Des. Territ. Sust 7(1). https://doi.org/10.5380/guaju.v7i1.76916
).

According to Plastics Europe (2023)Plastics Europe. 2023. Plastics - the Facts 2023: An analysis of European plastics production, demand and waste data. Available at https://www.plasticseurope.org/application/files/1115/7236/4388/FINAL_web_version_Plastics_the_facts2019_14102019.pdf. Accessed on 01/02/2023.
estimates, global plastic production reached 400 million t in 2022, including thermoplastics, highlighting its widespread use. Given its high production and disposal rates, plastic is considered a highly contaminating product and a global threat to environmental issues, food safety and human health (Sharma et al. 2017Sharma S., Chatterjee S. 2017. Microplastic pollution, a threat to marine ecosystem and human health: a short review. Environ. Sci. Poll. Res24: 21530-21547. https://doi.org/10.1007/s11356-017-9910-8
, Bessa et al. 2018Bessa F., Barría P., Net J.M., et al. 2018. Occurrence of microplastics in commercial fish from a natural estuarine environment. Mar. Pollut. Bull. 128: 575-584. https://doi.org/10.1016/j.marpolbul.2018.01.044
, Peixoto et al. 2019Peixoto D., Pinheiro C., Amorin J., et al. 2019. Microplastic pollution in commercial salt for human consumption: A review. Estuar. Coast. Shelf Sci. 219: 161-168. https://doi.org/10.1016/j.ecss.2019.02.018
, da Silva et al. 2022Da Silva E.F., Carmo D.F., Muniz M.C., et al. 2022. Evaluation of microplastic and marine debris on the beaches of Niteroi Oceanic Region, Rio De Janeiro, Brazil. Mar. Pollut. Bull 175: 113161. https://doi.org/10.1016/j.marpolbul.2021.113161
).

Once in the environment, plastics undergo weathering processes such as photodegradation, chemical breakdown and mechanical wear, leading to fragmentation and changes in properties such as colour. When these fragments measure between 5 mm and 0.1 µm, they are classified as microplastics, either secondary (from the breakdown of larger plastics) or primary (originally manufactured at this size, such as pellets and microspheres). Particles smaller than 0.1 µm are categorized as nanoplastics (Castro et al. 2016Castro R.O., Silva M.L., Marques M.R.C., et al. 2016. Evaluation of microplastics in Jurujuba Cove, Niterói, RJ, Brazil, an area of mussels farming. Mar. Pollut. Bull 110 (1): 555-558. https://doi.org/10.1016/j.marpolbul.2016.05.037
, Olivatto et al. 2018Olivatto G.P., Carreira R., Tornisielo V.L., et al. 2018. Microplásticos: Contaminantes de preocupação global no Antropoceno. Rev. Virtual Quím. 10. https://doi.org/10.21577/1984-6835.20180125
, Mercogliano et al. 2020Mercogliano R., Avio C.G., Regoli F., et al. 2020. Occurrence of Microplastics in Commercial Seafood under the Perspective of the Human Food Chain: A Review. J. Agric. Food Chem 68: 5296-5301. https://doi.org/10.1021/acs.jafc.0c01209
). Studies have widely documented microplastics and nanoplastics across aquatic, terrestrial and aerial environments, highlighting their extensive dispersion and ingestion across trophic levels, from plankton to humans (Sobral et al. 2011Sobral P., Frias J., Martins J. 2011. Microplástico nos oceanos - um problema sem fim à vista. Lisboa. Rev. Ecol. 3: 12-21.
, Hirata et al. 2017Hirata G., Viana E., Filho H.F., et al. 2017. Caracterização de pellets plásticos na Praia do Tombo, município do Guarujá, SP, Brasil. Rev. Int. Cienc 7(2): 202-216. https://doi.org/10.12957/ric.2017.29271
, Peixoto et al. 2019Peixoto D., Pinheiro C., Amorin J., et al. 2019. Microplastic pollution in commercial salt for human consumption: A review. Estuar. Coast. Shelf Sci. 219: 161-168. https://doi.org/10.1016/j.ecss.2019.02.018
, Zurier et al. 2020Zurier, H.S., Goddard, J.M. 2020. Biodegradation of microplastics in food and agriculture. Curr. Opin. Food Sci 37: 37-44. https://doi.org/10.1016/j.cofs.2020.09.001
).

Microplastics are known to carry pathogens and absorb various pollutants present in the marine environment, including persistent organochlorine pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pharmaceuticals and polybrominated diphenyl ethers. When these pollutants detach from ingested microplastics, they can be absorbed by marine organisms, potentially compromising their health and survival. Furthermore, the risk of biomagnification poses a hazard to top predators in the food chain, including humans, as prolonged exposure to these contaminants accumulates over time through the food web (Araújo et al. 2021Araújo F.V., Castro R.O., Silva M.L., et al. 2021. Ecotoxicological effects of microplastics and associated pollutants. In: Kibenge, Baldisserotto and Chong (eds), Aquaculture Toxicology, Academic Press, pp. 189-227. https://doi.org/10.1016/B978-0-12-821337-7.00009-8
).

When microplastics come into contact with skin or are inhaled or ingested, they can trigger oxidative stress and inflammatory lesions, affecting various human bodily systems, including cardiovascular, renal, respiratory, reproductive, gastrointestinal and neurological systems. This exposure can lead to serious health issues such as cancer and diabetes (Prata et al. 2020Prata J.C., da Costa J.P., Lopes I., et al. 2020. Environmental exposure to microplastics: an overview on possible human health effects. Sci. Total Environ 702: 134455. https://doi.org/10.1016/j.scitotenv.2019.134455
, UNEP, 2021United Nations Environment Programme - UNEP. 2021. Plastics Impacts on Human Health in the Pacific Region. Available at https://wedocs.unep.org/20.500.11822/37411. Accessed on 09/22/2022
). As a result, the inadvertent consumption of microplastics by a range of marine organisms poses a potential health risk to humans, even if the viscera are removed before consumption (Olivatto et al. 2018Olivatto G.P., Carreira R., Tornisielo V.L., et al. 2018. Microplásticos: Contaminantes de preocupação global no Antropoceno. Rev. Virtual Quím. 10. https://doi.org/10.21577/1984-6835.20180125
, De-la-Torre, 2020De-la-Torre G.E. 2020. Microplastics: an emerging threat to food security and human health. J. Food Sci. Technol 57: 1601-1608. https://doi.org/10.1007/s13197-019-04138-1
, Kutralam-Muniasamy et al. 2020Kutralam-Muniasamy G., Pérez-Guevara F., Elizalde-Martínez I., et al. 2020. Branded milks - Are they immune from microplastics contamination? Sci. Total Environ 714: 136823. https://doi.org/10.1016/j.scitotenv.2020.136823
, Zurier et al. 2020Zurier, H.S., Goddard, J.M. 2020. Biodegradation of microplastics in food and agriculture. Curr. Opin. Food Sci 37: 37-44. https://doi.org/10.1016/j.cofs.2020.09.001
).

Brazil’s average seafood consumption is around 5-10 kg per capita yearly (FAO, 2020FAO, Food and Agriculture Organization of the United Nations. 2020. El estado mundial de la pesca y la acuicultura. La sostenibilidad en acción. Rome. 223 pp.
). While mussels constitute a relatively small fraction of this consumption, their sessile and filter-feeding nature allows them to accumulate pollutants in the water, potentially amplifying health risks when ingested. These characteristics enable mussels to reveal environmental impacts that may otherwise go unnoticed (Resgalla et al. 2008Resgalla Jr C., Weber L.I., Conceição M.B., 2008. O mexilhão Perna perna (L.): biologia, ecologia e aplicações. Editora Interciência, Rio de Janeiro, RJ. 317 pp.
, Pierri et al. 2016Pierri B.S., Fossari T.D., Magalhães A.R.M., 2016. O mexilhão Perna perna no Brasil: Nativo ou exótico? Arq. Bras. Med. Vet. Zootec 68: 404-414. https://doi.org/10.1590/1678-4162-8534
, Cho et al. 2018Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
, Mercogliano et al. 2020Mercogliano R., Avio C.G., Regoli F., et al. 2020. Occurrence of Microplastics in Commercial Seafood under the Perspective of the Human Food Chain: A Review. J. Agric. Food Chem 68: 5296-5301. https://doi.org/10.1021/acs.jafc.0c01209
, Machado et al. 2021Machado J.Á., Oliveira S., Nazário M.G., et al. 2021. Análise da presença de microplástico em bivalves (Perna perna): um estudo de caso em Matinhos, litoral do Paraná. Rev. Bras. Des. Territ. Sust 7(1). https://doi.org/10.5380/guaju.v7i1.76916
). Li et al. (2019)Li J., Lusher A., Rotchell J.M., et al. 2019. Using mussels as a global bioindicator of coastal microplastic pollution. Environ. Pollut. https://doi.org/10.1016/j.envpol.2018.10.032
note that numerous researchers have suggested using mussels as indicators for microplastics in coastal areas.

Given their prevalence along the Brazilian coast and their popularity as a food source, especially in the southern and southeastern regions, the Perna perna mussel was chosen for this study. These mussels are harvested from natural beds and cultivated through aquaculture. According to IBGE (2023)IBGE - Instituto Brasileiro de Geografa e Estatística. 2023. Pesquisa da Pecuária Municipal 2020. Available at https://sidra.ibge.gov.br/tabela/3940#resultado. Accessed on 01/09/2023.
, Brazil’s total mussel production reached 15700 t, with the southeastern region alone contributing 82896 kg of oysters, mussels and scallops. This highlights the significance of mussel farming in the region’s seafood industry.

Mussel farming in Brazil utilizes longline systems, which involve nylon cables ranging from 50 to 100 m anchored to floats, typically large plastic barrels, to support cultivation nets. This method can support approximately 4 t of mussels (Valenti et al. 2021Valenti W.C., Barros H.P., Moraes-Valenti P., et al. 2021. Aquaculture in Brazil: past, present and future. Aquac. Rep 19: 100611. https://doi.org/10.1016/j.aqrep.2021.100611
). Once harvested, farmed mussels typically undergo a depuration process before being packaged for sale, ensuring they are clean and safe for consumption.

Given the prevalence of plastic waste in the environment and the plastic materials used in mussel farming, there is a critical need for research to assess the potential presence of microplastics in mussels available to consumers. We hypothesize that farmed mussels, which undergo a depuration process before sale, are less likely to be contaminated with microplastics than those harvested directly from natural sources.

Additionally, the findings from this study could inform future research aimed at establishing maximum permissible concentrations of these pollutants in water and mussels, ultimately reducing the risks associated with consuming these organisms.

Materials and methods

Sources of Mussels

 ⌅

Itaipu Beach (22°58'15"S, 43°2'47"W), located at the eastern end of Itaipu Cove in Niterói, is just 800 m long (Fig. 1A) (da Silva et al. 2021Da Silva E.F., Carmo D.F., Vezzone M., et al. 2021. Análise da percepção ambiental dos moradores do entorno das lagoas de Piratininga e Itaipu, Niterói (RJ). Rev. Bras. Edu. Amb 16(2): 446-469. https://doi.org/10.34024/revbea.2021.v16.11203
). It is bounded by the Itaipu Channel to the north and Andorinhas Hill to the south, formed by Precambrian gneiss. Due to its inland location, Itaipu Beach is the least susceptible to wave dynamics (Eccard et al. 2017Eccard L.R., Silva A.L.C., Silvestre C.P., 2017. Variações morfológicas nas praias oceânicas de Niterói (RJ, Brasil) em resposta a incidência de ondas de tempestades. Rev. Bras. Geogr. Fís. 10(1): 206-218.
). The beach and its surroundings experience high levels of real estate speculation and intense economic activity, including restaurants, bars and street vendors. This activity intensifies during the high season with the influx of tourists, serving nearby neighbourhoods that are home to families from various economic backgrounds (Timbó et al. 2019Timbó M., da Silva M.L., Castro R.O., et al. 2019. Diagnóstico da percepção ambiental dos usuários das praias de Itaipu e Itacoatiara quanto à presença de resíduos sólidos. J. Integr. Coast. Zone Manag 19 : 157-166. https://doi.org/10.5894/rgci-n75
, da Silva et al. 2021Da Silva E.F., Carmo D.F., Vezzone M., et al. 2021. Análise da percepção ambiental dos moradores do entorno das lagoas de Piratininga e Itaipu, Niterói (RJ). Rev. Bras. Edu. Amb 16(2): 446-469. https://doi.org/10.34024/revbea.2021.v16.11203
).

The mussel cultivation area is located at Cedro Beach, Palhoça, SC (27°44'93"S and 48°36'54"W), in a region between 6 to 8 m deep (Fig. 1B). Palhoça is situated in the Cubatão do Sul River Basin, which covers approximately 1451 km², consists of 51 micro-basins and is delimited by lands drained by the Cubatão do Sul River and its tributaries, such as the Vargem do Braço, Salto, Bugres, Cedro, Caldas do Norte (or das Forquilhas) and Matias rivers. The municipality’s coastal margin is also influenced by the Rio da Madre Basin covering an area of approximately 545 km² and consisting of 17 micro-basins (Novaes et al. 2010Novaes A.L.T., Santos A., Vianna L.F.N., et al. 2010. Planos Locais de Desenvolvimento da Maricultura de Santa Catarina - PLDM. Panorama da AQÜICULTURA, novembro, dezembro, 52-28. Available at https://www.researchgate.net/publication/272129159_Planos_Locais_de_Desenvolvimento_da_Maricultura_de_Santa_Catarina_-_PLDM/link/54db4f100cf233119bc5ccc5/download?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InB1YmxpY2F0aW9uIn19. Accessed on 01/06/2023.
).

Fig. 1.  Map showing the mussels' collection sites (red dot) analysed in this study. A - Itaipu Beach in Niterói, RJ, Brazil, from where the wild mussels were collected, and B, Cedro Beach, Santa Catarina, SC, Brazil, where the farmed mussels were collected.

Results

Quantification and characterization of microplastics

 ⌅

In total, 34 microplastics (all white fibres) were observed in the control samples (20 during the processing of the wild samples and 14 during the processing of the cultivated samples). These values were subtracted from the total value found in the respective samples.

The result (after deducting the values of the control experiments) showed fibre and film microplastic found in all analysed samples (Fig. 2). In the 1 kg portion of mussels purchased at Mercado São Pedro, sourced from Itaipu Beach, 145 microplastic particles were detected (0.145 particles g^-1), comprising 123 fibres (0.123 fibers g^-1) and 22 films (0.022 films g^-1). Most fibres were black (90%), followed by blue (4%), brown (2%) and red (0.8%). The films were mostly transparent (45.5%), with others being pink (27.3%) and green (13.6%) (Fig. 3).

Fig. 2.  Microplastic particles recovered from wild and cultivated mussels. A, B and F, fibres; C, D and E, films.

A total of 120 microplastic particles (0.12 particles g^-1) were found in the cultivated mussels purchased from supermarkets, consisting of 86 fibres (0.086 fibers g^-1) and 34 films (0.034 films g^-1). Among fibres, blue colour was prevalent, accounting for 44%. In the film particles, transparent microplastics predominated, making up 76.5% (Fig. 3).

Fig. 3.  Percentage of colours found in microplastic fibres and films found in wild (A) and cultivated (B) mussels.

The sizes of the recovered plastic particles were classified according to the standards set by UNEP (2021)United Nations Environment Programme - UNEP. 2021. Plastics Impacts on Human Health in the Pacific Region. Available at https://wedocs.unep.org/20.500.11822/37411. Accessed on 09/22/2022
and EFSA (2016)EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain). 2016. Statement on the presence of microplastics and nanoplastics in food, with particular focus on seafood. EFSA J. 14: 4501-4531. https://doi.org/10.2903/j.efsa.2016.4501
(Table 1).

Table 1.  Number of plastic particles recovered per kilogram found in wild and cultivated mussels

Classification	Wild		Cultivated
	Fibre	Film	Fibre	Film
Microplastic (0.001-<5 mm)	116	18	80	20
Mesoplastic (5-10 mm)	07	03	06	12
Macroplastic (>20 mm)	-	01	-	02
TOTAL	123	22	86	34
	145		120

Discussion

The presence of microplastics in both wild and farmed mussels is widely documented in the literature (Li et al. 2015Li J., Yang D., Li L., et al. 2015. Microplastics in commercial bivalves from China. Environ. Pollut. 207: 190-195. https://doi.org/10.1016/j.envpol.2015.09.018
, Li et al. 2018Li J., Green C., Reynolds A., et al. 2018. Microplastics in mussels sampled from coastal waters and supermarkets in the United Kingdom. Environ. Pollut. 241: 35-44. https://doi.org/10.1016/j.envpol.2018.05.038
, Barboza et al. 2018Barboza L.G.A., Vethaak A.D., Lavorante B.R.B.O., et al. 2018. Marine microplastic debris: An emerging issue for food security, food safety and human health. Mar. Pollut. Bull. 133: 336-348. https://doi.org/10.1016/j.marpolbul.2018.05.047
, Cho et al. 2018Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
, Mercogliano et al. 2020Mercogliano R., Avio C.G., Regoli F., et al. 2020. Occurrence of Microplastics in Commercial Seafood under the Perspective of the Human Food Chain: A Review. J. Agric. Food Chem 68: 5296-5301. https://doi.org/10.1021/acs.jafc.0c01209
), aligning with our findings. This occurrence can be attributed to the behaviour of mussels, which can filter up to 2 L of surrounding water per hour, as well as to the increasing prevalence of these pollutants in coastal waters, where natural beds and aquaculture farms are located (Van Cauwenberghe et al. 2015Van Cauwenberghe L., Claessens M., Vandegehuchte M.B., et al. 2015. Microplastics are taken up by mussels (Mytilus edulis) and lugworms (Arenicola marina) living in natural habitats. Environ. Pollut. 199: 10-17. https://doi.org/10.1016/j.envpol.2015.01.008
, Cho et al. 2018Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
, Mayoma et al. 2020Mayoma B.S., Sørensen C., Shashoua Y., et al. 2020. Microplastics in beach sediments and cockles (Anadara antiquata) along the Tanzanian coastline. Bull. Environ. Contam. and Toxicol 105: 513-521. https://doi.org/10.1007/s00128-020-02991-x
, Machado et al. 2021Machado J.Á., Oliveira S., Nazário M.G., et al. 2021. Análise da presença de microplástico em bivalves (Perna perna): um estudo de caso em Matinhos, litoral do Paraná. Rev. Bras. Des. Territ. Sust 7(1). https://doi.org/10.5380/guaju.v7i1.76916
). Mussels feed on what is carried by currents, including plankton and pollutants such as microplastics.

As in our results, the literature generally reports higher amounts of microplastics in wild mussels than in cultivated ones. Some authors (Van Cauwenbergh et al. 2015Van Cauwenberghe L., Claessens M., Vandegehuchte M.B., et al. 2015. Microplastics are taken up by mussels (Mytilus edulis) and lugworms (Arenicola marina) living in natural habitats. Environ. Pollut. 199: 10-17. https://doi.org/10.1016/j.envpol.2015.01.008
, Catarino et al. 2018Catarino A.I., Macchia V., Sanderson W.G., et al. 2018. Low levels of microplastics (MP) in wild mussels indicate that MP ingestion by humans is minimal compared to exposure via household fibres fallout during a meal. Environ. Pollut. 237: 675-684. https://doi.org/10.1016/j.envpol.2018.02.069
, Cho et al. 2018Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
) suggest that this difference may be due to pollution in the surrounding waters and intertidal zones, where bivalves commonly settle, exposing them to suspended microplastic particles. In contrast, cultivated mussels are typically located at depths greater than one metre and remain submerged for extended periods (or constantly) as a result of aquaculture setups.

The slight difference in microplastic values between wild (0.145 particles g^-1) and cultivated mussels (0.120 particles g^-1) in our study may be primarily due to the low levels found in wild mussels compared with other regions. For instance, Li et al. (2018)Li J., Green C., Reynolds A., et al. 2018. Microplastics in mussels sampled from coastal waters and supermarkets in the United Kingdom. Environ. Pollut. 241: 35-44. https://doi.org/10.1016/j.envpol.2018.05.038
reported concentrations of 0.7 to 2.9 particles g^-1 in mussels from United Kingdom coastal areas. Renzi (2018)Renzi M., Guerranti C., Blašković A., 2018. Microplastic contents from maricultured and natural mussels. Mar. Pollut. Bull. 131: 248-251. https://doi.org/10.1016/j.marpolbul.2018.04.035
also found higher levels in four Italian locations, ranging from 3.0 to 9.2 particles g^-1. Similarly, Li et al (2015)Li J., Yang D., Li L., et al. 2015. Microplastics in commercial bivalves from China. Environ. Pollut. 207: 190-195. https://doi.org/10.1016/j.envpol.2015.09.018
reported concentrations ranging from 2.1 to 10.5 particles g^-1 in nine Chinese commercial bivalve species, while another study reported 1.52 to 5.36 particles g^-1 (Qu et al. 2018Qu X., Su L., Li H., et al. 2018. Assessing the relationship between the abundance and properties of microplastics in water and in mussels. Sci. Total Environ 621: 679-686. https://doi.org/10.1016/j.scitotenv.2017.11.284
). All these authors commonly suggest that the main source of microplastics is the contamination of nearby areas, which is directly related to human activities.

In Niterói, Birnstiel et al. (2019)Birnstiel S., Soares-Gomes A., Gama B.A.P. 2019. Depuration reduces microplastic content in wild and farmed mussels. Mar. Pollut. Bull. 140: 241-247. https://doi.org/10.1016/j.marpolbul.2019.01.044
recorded 6.67 particles g^-1 in Perna perna mussels collected from Eva Beach and 4.12 particles g^-1 from Jurujuba Beach. Although these beaches are close to Itaipu Beach, they are in sheltered coves within Guanabara Bay, a known polluted area with high microplastic loads (Castro et al. 2016Castro R.O., Silva M.L., Marques M.R.C., et al. 2016. Evaluation of microplastics in Jurujuba Cove, Niterói, RJ, Brazil, an area of mussels farming. Mar. Pollut. Bull 110 (1): 555-558. https://doi.org/10.1016/j.marpolbul.2016.05.037
, Birnstiel et al. 2019Birnstiel S., Soares-Gomes A., Gama B.A.P. 2019. Depuration reduces microplastic content in wild and farmed mussels. Mar. Pollut. Bull. 140: 241-247. https://doi.org/10.1016/j.marpolbul.2019.01.044
, Castro et al. 2020Castro R.O., Silva M.L., Marques M.R.C. et al. 2020. Spatio-temporal evaluation of macro, meso and microplastics in surface waters, bottom and beach sediments of two embayments in Niterói, RJ, Brazil. Mar. Pollut. Bull. 160: 111537. https://doi.org/10.1016/j.marpolbul.2020.111537
). According to Castro et al. (2020)Castro R.O., Silva M.L., Marques M.R.C. et al. 2020. Spatio-temporal evaluation of macro, meso and microplastics in surface waters, bottom and beach sediments of two embayments in Niterói, RJ, Brazil. Mar. Pollut. Bull. 160: 111537. https://doi.org/10.1016/j.marpolbul.2020.111537
, the waters of Itaipu, where wild mussels were collected, exhibited relatively low microplastic concentrations, ranging from 1.2 particles m^-3 in winter to 2.86 particles m^-3 in summer. The Itaipu Beach area is significantly influenced by ocean waters, which promote the easy dispersal of microplastic particles due to local hydrodynamics, potentially explaining the lower concentration of mussels from this area.

Another possible explanation for the lower difference in values between wild and cultivated mussels in this study could be the depuration process, which the latter undergo after harvesting and before packaging. Birnstiel et al. (2019)Birnstiel S., Soares-Gomes A., Gama B.A.P. 2019. Depuration reduces microplastic content in wild and farmed mussels. Mar. Pollut. Bull. 140: 241-247. https://doi.org/10.1016/j.marpolbul.2019.01.044
demonstrated that microplastic concentrations in cultivated mussels in Niterói decreased by 28.95% after 93 hours of depuration. This process can reduce larger particle concentrations (Van Cauwenberghe and Janssen, 2014Van Cauwenberghe L., Janssen C.R. 2014. Microplastics in bivalves cultured for human consumption. Environ. Pollut. 193: 65-70. https://doi.org/10.1016/j.envpol.2014.06.010
). These authors found that depuration with HNO₃ lowered the microplastic concentration by around 30% after three days, although smaller particles persisted, suggesting potential translocation through the intestinal wall into tissues and the circulatory system. This is corroborated by the continued presence of microplastics in organisms even post-depuration, but differs from our results, as we found a greater quantity of larger particles in cultivated mussels.

The values obtained in this study for cultivated mussels were below those reported by Van Cauwenberghe and Janssen (2014)Van Cauwenberghe L., Janssen C.R. 2014. Microplastics in bivalves cultured for human consumption. Environ. Pollut. 193: 65-70. https://doi.org/10.1016/j.envpol.2014.06.010
, who found microplastic concentrations in Mytilus edulis of 0.36±0.07 particles g^-1 before depuration and 0.24±0.07 particles g^-1 afterward, and in Crassostrea gigas (0.47±0.16 particles g^-1 before depuration and 0.35±0.05 particles g^-1 afterward). Likewise, Li et al. (2018)Li J., Green C., Reynolds A., et al. 2018. Microplastics in mussels sampled from coastal waters and supermarkets in the United Kingdom. Environ. Pollut. 241: 35-44. https://doi.org/10.1016/j.envpol.2018.05.038
observed concentrations ranging from 0.9 to 1.4 particles g^-1 in mussels purchased from supermarkets and Cho et al. (2018)Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
reported values up to 1.08 particles g^-1 in mussels from a fish market in southern Korea.

The lower value found in this study (0.12 items g^-1 in cultivated mussels) corresponds to approximately 2% of the average daily microplastic intake per person (100 to 140 particles/day according to Cox et al. 2019Cox K.D., Covernton G.A., Davies H.L., et al. 2019. Human Consumption of Microplastics. Environ. Sci. Technol. 53, 12: 7068-7074. https://doi.org/10.1021/acs.est.9b01517
), assuming a daily seafood intake of 20 g in Brazil (FAO, 2020FAO, Food and Agriculture Organization of the United Nations. 2020. El estado mundial de la pesca y la acuicultura. La sostenibilidad en acción. Rome. 223 pp.
). These values are only estimates, as mussel consumption in Brazil constitutes only a portion of total seafood consumption, but in the south and southeast regions where this consumption is higher, this daily intake may represent a higher percentage, increasing the risk of consuming these molluscs.

It is important to note that the varying concentrations of microplastics reported in various studies may also be influenced by the methodologies used to dissolve organisms. There is no standardized protocol for recovering microplastics in seafood (EFSA, 2016EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain). 2016. Statement on the presence of microplastics and nanoplastics in food, with particular focus on seafood. EFSA J. 14: 4501-4531. https://doi.org/10.2903/j.efsa.2016.4501
, Catarino et al. 2018Catarino A.I., Macchia V., Sanderson W.G., et al. 2018. Low levels of microplastics (MP) in wild mussels indicate that MP ingestion by humans is minimal compared to exposure via household fibres fallout during a meal. Environ. Pollut. 237: 675-684. https://doi.org/10.1016/j.envpol.2018.02.069
, Cho et al. 2018Cho Y., Shim W.J., Jang M., et al. 2018. Abundance and characteristics of microplastics in market bivalves from South Korea. Environ. Pollut. 245: 1107-1116. https://doi.org/10.1016/j.envpol.2018.11.091
, Digka et al. 2018Digka N., Tsangaris C., Torre M., et al. 2018. Microplastics in mussels and fish from the Northern Ionian Sea. Mar. Pollut. Bull 135: 30-40. https://doi.org/10.1016/j.marpolbul.2018.06.063
, Li et al. 2018Li J., Green C., Reynolds A., et al. 2018. Microplastics in mussels sampled from coastal waters and supermarkets in the United Kingdom. Environ. Pollut. 241: 35-44. https://doi.org/10.1016/j.envpol.2018.05.038
). The choice of chemical agents and their concentrations can partially or completely damage microplastics, affecting their size and colour.

Our study used 5% NaOH, a concentration that falls outside the range specified by Lusher et al. (2017)Lusher A.L., Welden N.A., Sobral P., et al. 2017. Sampling, isolating and identifying microplastics ingested by fish and invertebrates. Anal. Methods 9: 1346-1360. https://doi.org/10.1039/C6AY02415G
. This concentration is unlikely to damage the main types of microplastic particles frequently reported in the literature, including polypropylene, polyethylene, polyvinyl chloride and polyethylene terephthalate.

The microplastic particles shown in this study displayed chemical similarities to nylon (polyamide), chlorinated polyethylene and chlorosulphonated polyethylene, with fibres and films identified as the main morphological types. Plastic fibres and films are commonly found in marine environments and were predominantly described in Guanabara Bay, a region close to Itaipu, by Baptista Neto et al. (2019)Baptista Neto J.A., de Carvalho D.G., Medeiros K., et al. 2019. The impact of sediment dumping sites on the concentrations of microplastic in the inner continental shelf of Rio de Janeiro/Brazil. Mar. Pollut. Bull. 149: 110558. https://doi.org/10.1016/j.marpolbul.2019.110558
. Similarly, Brocardo (2022)Brocardo, G.S. 2022. Avaliação da presença de microplásticos (MPs) em três espécies de bivalves cultivadas na Ilha de Santa Catarina, Brasil. Undergraduate thesis, Federal University of Santa Catarina. Available at https://repositorio.ufsc.br/handle/123456789/243120. Accessed on 09/22/2022.
reported that fibres (75%) and fragments (25%) were the predominant microplastic forms in mussels from farming sites on Santa Catarina Island, close to the area of the current study. Fibres found in our study were all characterized as polyamide and were the total samples from farmed mussels. Birnstiel et al. (2019)Birnstiel S., Soares-Gomes A., Gama B.A.P. 2019. Depuration reduces microplastic content in wild and farmed mussels. Mar. Pollut. Bull. 140: 241-247. https://doi.org/10.1016/j.marpolbul.2019.01.044
, studying microplastics in a farming area in Jurujuba, Niterói, RJ, also reported a high prevalence of polyamide in fibre form. These authors proposed that these detected fibres may have secondary sources, potentially originating from synthetic fabrics or maritime ropes, given the higher density of polyamide relative to polyethylene, the fact that mussels are farmed at depths greater than one metre and remain submerged for long periods, and the use of nylon ropes in these aquaculture structures.

In the Itaipu area, where wild mussels were collected, there is a fishing community, and the presence of polyamide fibres in the mussels from this area can be explained by fibre contamination from fishing gear used by these fishermen. The films analysed in mussels from Itaipu were characterized as chlorinated polyethylene and chlorosulphonated polyethylene. These compounds were also described by Castro et al. (2020)Castro R.O., Silva M.L., Marques M.R.C. et al. 2020. Spatio-temporal evaluation of macro, meso and microplastics in surface waters, bottom and beach sediments of two embayments in Niterói, RJ, Brazil. Mar. Pollut. Bull. 160: 111537. https://doi.org/10.1016/j.marpolbul.2020.111537
when they analysed the waters of this location. These compounds are used in various products and provide these products with resistance and durability against environmental stressors such as UV degradation. These characteristics may explain their availability in Itaipu’s waters, influenced by Guanabara Bay, a region heavily contaminated with microplastics, and their subsequent ingestion by mussels from natural beds.

These results support the hypothesis that improper waste disposal and fishing materials are sources of plastic particle contamination in the marine environment.

In this study, the most prevalent colours of microplastic particles were black and transparent, with blue also being common in mussels from cultivated sources. The prevalence of blue particles aligns with findings from Digka et al. (2018)Digka N., Tsangaris C., Torre M., et al. 2018. Microplastics in mussels and fish from the Northern Ionian Sea. Mar. Pollut. Bull 135: 30-40. https://doi.org/10.1016/j.marpolbul.2018.06.063
and Brocardo (2022)Brocardo, G.S. 2022. Avaliação da presença de microplásticos (MPs) em três espécies de bivalves cultivadas na Ilha de Santa Catarina, Brasil. Undergraduate thesis, Federal University of Santa Catarina. Available at https://repositorio.ufsc.br/handle/123456789/243120. Accessed on 09/22/2022.
, which indicate that blue is characteristic of plastics used in longline structures such as ropes and suspension buoys. This blue coloration was consistently observed in the studies by Birnstiel et al. (2019)Birnstiel S., Soares-Gomes A., Gama B.A.P. 2019. Depuration reduces microplastic content in wild and farmed mussels. Mar. Pollut. Bull. 140: 241-247. https://doi.org/10.1016/j.marpolbul.2019.01.044
and Castro et al. (2020)Castro R.O., Silva M.L., Marques M.R.C. et al. 2020. Spatio-temporal evaluation of macro, meso and microplastics in surface waters, bottom and beach sediments of two embayments in Niterói, RJ, Brazil. Mar. Pollut. Bull. 160: 111537. https://doi.org/10.1016/j.marpolbul.2020.111537
carried out in the same areas as the present study.

Regardless of their origin, our results show that mussels accumulate microplastics and most likely reflect the presence of these pollutants in their environment, highlighting their suitability for monitoring pollution levels. This reinforces the importance of using mussels as indicators of plastic contamination in marine ecosystems, providing valuable data that can inform both environmental management practices and public health concerns.

Conclusion

This study aimed to quantify and characterize microplastic particles and their chemical composition in Perna perna mussels sold in Niterói and sourced from aquaculture farms and natural habitats. According to previous studies conducted in the regions studied, the quantity, colour and chemical composition of the microplastics found in wild and cultivated mussels suggest a strong influence from the surrounding environment.

Although the values found in wild and cultivated mussels were lower than those reported in other studies, it is evident that the population consumes contaminated mussels, regardless of whether they are wild or cultivated, putting their health at risk. Management measures, especially in areas designated for mussel cultivation, must be implemented to prevent the presence of plastic waste in these environments. Additionally, given the use of plastic materials in cultivation structures, mandatory depuration of these mussels before commercialization should be enforced.

Declaration of competing interests

The authors of this article declare that they have no financial, professional or personal conflicts of interest that could have inappropriately influenced this work.

Funding sources

Thanks to FAPERJ (Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro), CAPES (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) for the grants given to the authors.

Authorship contribution statement

Lucas A. L. Rocha: Formal analysis, Investigation, Methodology, Project administration, Writing - original draft. Helena A. Portela: Project administration, Writing - review & editing. Mônica R. C. M. Calderari: Methodology, Writing - review & editing. Fábio V. Araújo: Conceptualization, Formal analysis, Funding acquisition, Methodology, Project administration, Writing - review & editing.

References